How to send red squirrel bodies for post mortem

Advice on how and where to send dead red squirrels for post mortem can be found here.


  • Derbridge, J. J. & Koprowski, J. L. (2019) Experimental removals reveal dietary niche partitioning facilitates coexistence between native and introduced species. Ecology and Evolution 0(0).

Abstract: Niche overlap between native species and ecologically similar invaders can lead to competitive exclusion of threatened native species, but if two such species also co-occur naturally elsewhere, interactions between native and introduced populations may mirror coevolved niche partitioning that reduces competition and promotes coexistence. A single, insular population of Fremont?s squirrel (Tamiasciurus fremonti) the Mount Graham red squirrel (MGRS; T. f. grahamensis) in the Pinaleño Mountains, Arizona, USA, is critically endangered and resource competition with introduced Abert’s squirrels (Sciurus aberti) may threaten its long-term persistence. The species are naturally synoptic in other mountain sites, and both consume diets comprised primarily of conifer seeds and fungi. We conducted experimental removals of introduced Abert’s squirrels and used stable isotope analysis of diets before and after removals, and of diets in naturally syntopic populations to test the hypothesis that dietary niche partitioning can facilitate coexistence between native and introduced species. We also developed a novel approach to determine the influence of fluctuating food availability on carbon enrichment in consumers. Mount Graham red squirrels and introduced Abert’s squirrels partitioned the dietary niche similarly to naturally syntopic populations. Removals had no apparent effect. Diet of MGRS was more closely linked to availability of resources than to presence of Abert’s squirrels. Flexible dietary niche of introduced Abert’s squirrels may have allowed them to exploit a resource opportunity in syntopy with MGRS. Variable food production of MGRS habitat may intensify competition in poor years, and territorial defense against non-native Abert’s squirrels likely imposes fitness costs on individual MGRS. Similarity in our model species? diets may make MGRS more vulnerable to competition if climate change eliminates the advantages of larder-hoarding. Where introduced populations of ecologically similar species are better adapted to changing conditions, they may ultimately replace southern peripheral populations of native species.

  • Di Febbraro, M., Menchetti, M., Russo, D., Ancillotto, L., Aloise, G., Roscioni, F., Preatoni, D. G., Loy, A., Martinoli, A., Bertolino, S. & Mori, E. (2019) Integrating climate and land-use change scenarios in modelling the future spread of invasive squirrels in Italy. Diversity and Distributions 0(0).


Aim The establishment and spread of invasive alien species may be influenced by several mutually interacting factors, whose understanding is paramount to develop effective biosecurity policies. However, studies focused on modelling spatially explicit patterns of future invasion risk have so far focused on species response to climate change impacts, while land-use change has been neglected. We investigated how the interplay between climate and land-use change could affect the future potential distribution and dispersal corridors of four alien squirrels introduced to Europe (Sciurus carolinensis, Callosciurus finlaysonii, Callosciurus erythraeus and Eutamias sibiricus).

Location and Methods Our study was conducted in Italy. We used Species Distribution Models and circuit theory methods to test whether future scenarios based only on climate change predict a different effect on range and connectivity of alien squirrel populations, compared to scenarios that include both climate and land-use changes.

Results Scenarios based only on climate change predicted a range increase and a high geographic stability (>50%) for most species, with different, yet limited, effects on connectivity corridors. Conversely, scenarios based on both climate and land-use change showed a loss in range extent and a low geographic stability (<50%) of both range and dispersal corridors for most species.

Main conclusions Scenarios considering both climate and land-use change provide predictions on invasion risk that overturn those including only climate change. The effect of global warming alone would lead to a considerable range expansion of all species. Conversely, when land-use change is added, a potential loss in suitable habitat and dispersal corridors is predicted for alien squirrels, hence limiting their range expansion. We recommend using multiple drivers in models to obtain reliable predictions for implementing biosecurity policies related to invasive alien species.

  • Hämäläinen, S., Fey, K. & Selonen, V. (2018) Habitat and nest use during natal dispersal of the urban red squirrel (Sciurus vulgaris). Landscape and Urban Planning 169: 269-275.

As urban environments differ from the natural environment, the ability of a species to move in and use variable land composition types determines its fate in the urban environment. In many mammalian species, the selection of home ranges mainly occurs during natal dispersal. Thus, habitat selection of juvenile individuals greatly determines where animals are found in the city. Here, our goal is to understand how an originally forest-dwelling rodent selects components of an urban habitat. We used radio telemetry to record the habitat and nest use of Eurasian red squirrels (Sciurus vulgaris) in the city of Turku in southwestern Finland, with the main focus on habitat use during natal dispersal. We found that although the red squirrels preferred areas with more trees available than in the surrounding urban landscape they nevertheless often used sites with only a few trees. This result was highlighted by the analysis of the home range scale, as the area used did not differ greatly from the habitat composition of the available landscape. Juvenile red squirrels used the deciduous land cover type more often during movements in the natal area than during dispersal and explorative movements; however, they also settled in areas with less deciduous land cover type than in the natal area. Our results show that in urban areas movements of red squirrels are not restricted to their natural habitat type, which is a coniferous forest, but that they seem to be well adapted to urban areas, being able to utilize urban structures.

  • Jagiello, Z. A., Dyderski, M. K. & Dylewski, Ł. (2019) What can we learn about the behaviour of red and grey squirrels from YouTube? Ecological Informatics 51: 52-60.

Abstract: Citizen science has emerged as an important tool in biology, ecology, and conservation studies. In this paper, we examined YouTube (YT) videos featuring the behaviour of red (Sciurus vulgaris) and grey (Sciurus carolinensis) squirrels in Europe, in both urban and forest habitats. Our study shows that specific behaviours of these squirrels, such as aggression, grooming and calling, have frequently been recorded on YT videos. The present paper uses this open data for the first time to compare differences between the frequency of some types of behaviour in two habitats. Based on detrended correspondence analysis, we show a significant difference in sets of behaviours between two squirrel species. Our investigation show that YT can be a source for monitoring the behaviour of wild species, especially in urban habitats, thus affording insights into the species plasticity of urban individuals. YT, as part of citizen science, is a potential source of information in behavioural ecology.

  • Jokinen, M., Hanski, I., Numminen, E., Valkama, J. & Selonen, V. (2019) Promoting species protection with predictive modelling: Effects of habitat, predators and climate on the occurrence of the Siberian flying squirrel. Biological Conservation 230: 37-46.

Abstract: Species distribution models (SDMs) can be used to predict species occurrence and to seek insight into the factors behind observed spatial patterns in occurrence, and thus can be a valuable tool in species conservation. In this study, we used MaxEnt software to explain the occurrence of a protected forest-dwelling species, the Siberian flying squirrel. We produce occurrence maps covering the main distribution area for the species in the European Union. Using an exceptionally extensive presence-absence dataset collected with a standardized method, we evaluated the relative role of predation pressure, climate, and amount of habitat affecting flying squirrel occurrence. We found that regional variation in mean winter temperature had relatively large predictive power for flying squirrel occurrence. In addition, the regional abundance of flying squirrels was partly explained by differences in predation pressure. The results also support the conclusion that areas with older forests and nearby agricultural areas are optimal for the species. Our study shows that multiple factors affect the species’ occurrence in large spatial scales. We also conclude that climate is having a large effect on species occurrence, and thus the changing climate has to be taken into account in conservation planning. Our results help conservation managers in targeting surveys and protection measures on various spatial scales, and decision makers in focusing on the factors that drive the species’ occurrence. Our results also indicate that we would need additional tools and measures in the EU for achieving a favourable conservation status of those species that occur in commercial forests.

  • Olson, E. R., Martin, J. G., Anich, P. S. & Kohler, A. M. (2019) Ultraviolet fluorescence discovered in New World flying squirrels (Glaucomys). Journal of Mammalogy.

Abstract: Fluorescence of visible wavelengths under ultraviolet (UV) light has been previously detected in a wide range of birds, reptiles, and amphibians and a few marsupial mammals. Here, we report the discovery of vivid UV fluorescence of the pelage in Glaucomys, the New World flying squirrels. Fluorescence in varying intensities of pink was observed in females and males of all extant species (G. oregonensis, G. sabrinus, and G. volans) across all sampled geographic areas in North and Central America and a temporal range of 130 years. We observed fluorescence in museum specimens (n = 109) and wild individuals (n = 5) on both dorsal and ventral surfaces. Museum specimens of three co-occurring, diurnal sciurid species (Sciurus carolinensis, S. niger, and Tamiasciurus hudsonicus) were also examined but did not fluoresce. The ecological significance of this trait in the nocturnal–crepuscular flying squirrels warrants further investigation.

  • Pagès, M., Fischer, A., van der Wal, R. & Lambin, X. (2019) Empowered communities or “cheap labour”? Engaging volunteers in the rationalised management of invasive alien species in Great Britain. Journal of Environmental Management 229: 102-111.

Abstract: Volunteers are increasingly involved in the delivery of nature conservation policies, usually supported by a twofold rationale: volunteering can (a) enhance citizen participation in environmental governance and (b) ensure a workforce is in place to support conservation work in times of budget shortages. Here, we ask how these two rationales correspond to volunteers’ own motivations to engage in a specific nature conservation activity, namely the control of invasive alien species (IAS). We use qualitative interviews with professional project managers, local group leaders, and volunteers to examine the interactions between policies aiming to rationalise the management of IAS and the motivations for and goals of volunteer engagement. Our findings suggest that although volunteering can lead to positive conservation outcomes, satisfying experiences and empowerment, the different interests do not always align in practice. We investigate the implications of strategies that aim to improve the efficiency of invasive species and volunteer management, and discuss organisational arrangements that reconcile different objectives.

  • Pedreschi, D., García-Rodríguez, O., Yannic, G., Cantarello, E., Diaz, A., Golicher, D., Korstjens, A. H., Heckel, G., Searle, J. B., Gillingham, P., Hardouin, E. A. & Stewart, J. R. (2019) Challenging the European southern refugium hypothesis: Species-specific structures versus general patterns of genetic diversity and differentiation among small mammals. Global Ecology and Biogeography 28(2): 262-274.

Abstract: Aim In this study, we conduct a quantitative meta-analysis to investigate broad patterns of genetic variation throughout large geographical regions in order to elucidate concordant geographical patterns across species and identify common historical processes to better inform the ?cryptic refugia? versus the traditional ?southern refugia? hypothesis debate. Location Europe. Time period Late Pleistocene to present day. Major taxa studied Small mammals (Rodentia, Eulipotyphla). Methods A meta-analysis was performed on large-scale patterns of genetic diversity for 19 species from 59 papers. For each species, haplotype and nucleotide diversity were calculated using the mitochondrial D-loop and compared to the species? range. Results No consistent patterns were observed between mitochondrial DNA (mtDNA) diversity indices (nucleotide and haplotype diversity) and any of the indicators of distribution examined [latitude and longitude (max, min, centre, range)]. The patterns of genetic diversity observed in all the 19 species studied appear to be species-specific. Main conclusions In contrast to the traditional southern refugial hypotheses, we found no evidence for a consistent south?north post-glacial expansion. Instead individual species appear to respond to climate oscillations in niche-specific ways. This individual nature of each species? phylogeographical history indicates a complex web of post-glacial recolonization dynamics across Europe.

  • Scapin, P., Ulbano, M., Ruggiero, C., Balduzzi, A., Marsan, A., Ferrari, N. & Bertolino, S. (2019) Surgical sterilization of male and female grey squirrels (Sciurus carolinensis) of an urban population introduced in Italy. Journal of Veterinary Medical Science.

We report a successful surgical sterilization procedure for population control of 324 male and female free-ranging grey squirrels (Sciurus carolinensis) in Genoa (Italy). We describe the clinical procedure from the trapping of the animals to their surgical sterilization and release in another part of the city. Live-trapped squirrels were transported to the veterinary clinic within 1-2 hr of capture and maintained in a hospitalization room reserved for them. The waiting period before surgery was kept below 12 hr. The developed procedure has resulted in a survival of 94% of trapped squirrels from surgery to animal release. Sterilized squirrels started to feed in a very short time (1.0-1.5 hr), and after 2-3 days, it was possible to release them in a new area. Amoxicillin was used as a long-acting postoperative antibiotic to reduce the period of captivity. The successful surgical procedure described here can provide an important additional tool for the management of introduced populations of squirrels. We showed that the surgical sterilization of some hundred squirrels is clinically possible and could be included in management strategies aimed at removing critical populations of these species. Moreover, the data allow dosages and operational times in order to provide economic viability assessment of future population control measures.

  • Schilling, A.-K., Avanzi, C., Ulrich, R. G., Busso, P., Pisanu, B., Ferrari, N., Romeo, C., Mazzamuto, M. V., McLuckie, J., Shuttleworth, C. M., Del-Pozo, J., Lurz, P. W. W., Escalante-Fuentes, W. G., Ocampo-Candiani, J., Vera-Cabrera, L., Stevenson, K., Chapuis, J.-L., Meredith, A. L. & Cole, S. T. (2019) British Red Squirrels Remain the Only Known Wild Rodent Host for Leprosy Bacilli. Frontiers in Veterinary Science 6: 8.

Abstract: Eurasian red squirrels (Sciurus vulgaris) in the British Isles are the most recently discovered animal reservoir for the leprosy bacteria Mycobacterium leprae and Mycobacterium lepromatosis. Initial data suggest that prevalence of leprosy infection is variable and often low in different squirrel populations. Nothing is known about the presence of leprosy bacilli in other wild squirrel species despite two others (Siberian chipmunk [Tamias sibiricus], and Thirteen-lined ground squirrel [Ictidomys tridecemlineatus]) having been reported to be susceptible to experimental infection with M. leprae. Rats, a food-source in some countries where human leprosy occurs, have been suggested as potential reservoirs for leprosy bacilli, but no evidence supporting this hypothesis is currently available. We screened 301 squirrel samples covering four species (96 Eurasian red squirrels, 67 Eastern grey squirrels (Sciurus carolinensis), 35 Siberian chipmunks, and 103 Pallas’s squirrels (Callosciurus erythraeus)) from Europe and 72 Mexican white-throated woodrats (Neotoma albigula) for the presence of M. leprae and M. lepromatosis using validated PCR protocols. No DNA from leprosy bacilli was detected in any of the samples tested. Given our sample-size, the pathogen should have been detected if the prevalence and/or bacillary load in the populations investigated were similar to those found for British red squirrels.

  • Starkey, A. & delBarco-Trillo, J. (2019) Supplementary feeding can attract red squirrels (Sciurus vulgaris) to optimal environments. Mammalian Biology 94: 134-139.

Abstract: A number of conservation approaches are used to manage threatened species. However, some of these approaches require intensive planning and can often be restricted by funding. Supplementary feeding is a non-invasive and cost-effective approach to manage vulnerable populations, but we lack data on its usefulness. Here we investigated the effects of supplementary feeding on a population of red squirrels (Sciurus vulgaris), a UK priority species which faces competition from the non-native grey squirrel (Sciurus carolinensis). The study took place October-December 2015, lasting 8 weeks. Twenty feeders were installed 1 week prior to the beginning of the study in a protected woodland free from grey squirrels, either containing food (full feeders) or no food (empty feeders), and squirrel abundance before and after feeding was recorded at each feeder (for a total of 27 feeding and recording events). Six times more squirrels were seen at full feeders, and numbers increased by 7 fold after feeding. We also observed that the activity of red squirrels in the vicinity of full feeders increased during the course of the study. Eighty-five hair samples were collected during the study, all of which were found at full feeders. Results demonstrate red squirrels can differentiate between full and empty feeders, suggesting their awareness increases when supplementary food is present. Increased abundance of squirrels at full feeders after feeding times not only implies that squirrels are attracted to and can benefit by supplementation, it also shows that food supplementation can be used to regulate the movement of individuals across habitats. Understanding how red squirrel populations are affected by supplementary feeding will contribute towards existing conservation efforts to improve this species future survival.

  • Stirkė, V. (2019) Ecological aspects of Red Squirrel (Sciurus vulgaris) dreys in city parks. Acta Zoologica Academiae Scientiarum Hungaricae 65(1): 75-84.

Modified habitats often pose challenges to native fauna. Red Squirrels (Sciurus vulgaris) successfully inhabits territory of the cities. However research on quite abundant Red Squirrel populations in urban parks of Lithuania was lacking. The investigation was carried out in two city parks (area of Giruliai park 152 ha, Pasakų park forest – 31 ha) in Vilnius, Lithuania. Both areas were mainly coniferous, dominated with pine (Pinus sylvestris). Drey (N = 415) counts were done in February and March 2014–2016. Dreys were found in eight tree species. The Red Squirrels’ dreys were mainly built in most widespread tree species: pine (84.8% of all dreys) and birch (8.1%). Most of the found dreys were built on the side branches at the stem (47.7%). 21.8% of the dreys were built on the branches further from the stem, 18.5% on the top branches and 12% in the stem fork-off. Most of the dreys were set in the southern exposition (33.9%). Average number of red squirrels in both parks in 2014–2016 was 0.20±0.01 squirrels/ha, the average number of dreys – 0.75±0.05 dreys/ha. The population of urban red squirrels in Vilnius city parks can be regarded as stable and having medium abundance, which is supported by supplementary feeding.

  • Trapp, S. E., Day, C. C., Flaherty, E. A., Zollner, P. A. & Smith, W. P. (2019) Modeling impacts of landscape connectivity on dispersal movements of northern flying squirrels (Glaucomys sabrinus griseifrons). Ecological Modelling 394: 44-52.

Abstract: Landscape connectivity is a key component for successful dispersal of wildlife. Many approaches to quantify landscape connectivity utilize landscape characteristics and wildlife behavior in response to those characteristics, whereas other approaches focus on wildlife dispersal behavior. Combining landscape structure and wildlife behavior (e.g. movement, food acquisition, response to predation risk) provides critical information for conservation and management of many species. Individual-based models (IBM) are useful tools for evaluating the interaction between landscape characteristics and individual behaviors, thereby providing insights into management and conservation. Our objective was to evaluate the effect of reductions in landscape connectivity on northern flying squirrel dispersal movements under alternative timber management scenarios within the modeling framework of a spatially-explicit IBM. We simulated timber harvests of 6% and 9% of old-growth forest, the primary habitat for this species, distributed across 5, 10 or 15 harvest locations. We measured the influence of these scenarios upon landscape connectivity for flying squirrels. Landscapes with greater connectivity exhibited longer flying squirrel dispersal distances, more sinuous dispersal paths, and a greater total area of landscape utilization. However, connectivity was not directly correlated with habitat loss. The harvest scenario with 6% harvest of old growth distributed among 15 harvest locations had the lowest connectivity index value despite other scenarios modeling a greater percentage of old growth loss. The IBM demonstrated the importance of behaviors such as path tortuosity and movement rates in conjunction with landscape configuration in influencing the movement of dispersing individuals. The spatially explicit IBM provided a framework to evaluate connectivity from a fine-scale behavioral rather than structural perspective as well as to evaluate the distribution of new home range locations, which could be a useful management tool when evaluating the influence of landscape heterogeneity and stochastic behavior on wildlife movement and dispersal.

  • Waterman, J. M. & Archibald, A. J. (2019) Both familiarity and kinship influence odour discrimination by females in a highly social African ground squirrel. Animal Behaviour 148: 145-151.

Abstract: Kin recognition can be important in species where inbreeding avoidance or nepotism (favouritism towards kin) rely on identifying kin, particularly in species with alloparental care. The mechanisms that facilitate kin discrimination, where recognition is determined through cues that correlate with relatedness, usually include either prior association (familiarity) or phenotype matching or both. Odour is an important cue used in a number of mammalian species to discern kin, particularly the ground-dwelling squirrels. Cape ground squirrels, Xerus inauris, are a cooperative-breeding species, living in tight-knit family groups. However, group fission, promiscuity and the large home ranges of breeding males result in a high variance in relatedness both within and among social groups, making them a good species to investigate kin discrimination. We examined whether females are capable of discriminating between the odours of familiar versus unfamiliar females that varied in their relatedness to the focal female using odour experiments. Overall, the average duration of sniffing of the odours of familiar and unfamiliar females did not differ. Similarly, females did not adjust their sniff duration relative to the degree of relatedness of familiar females. However, females appeared to discriminate by the degree of relatedness of unfamiliar (stranger) females, spending longer sniffing odours from females that were not related to them. Thus, females were capable of discriminating the degree of relatedness from odour but they did not do so within their family group. We conclude that Cape ground squirrels are able to discriminate kin. However, whether females in this facultative cooperative breeder use the degree of relatedness in direct social interactions and nepotistic behaviours remains to be investigated.

Yi, X., Bartlow, A. W., Curtis, R., Agosta, S. J. & Steele, M. A. (2019) Responses of seedling growth and survival to post-germination cotyledon removal: an investigation among seven oak species. Journal of Ecology 0(ja).


  1. Rodents regularly rely on emerged epicotyls to locate and remove cotyledons still containing valuable nutrients. However, the extent to which acorn characteristics influence tolerance to post-germination predation has received little attention.
  2. Here, we investigated the impact of cotyledon removal following epicotyl emergence on seedling performance and survival of seven oak (Quercus) species. We imitated cotyledon predation at different stages of seedling establishment and development in order to detect effects on seedling height, leaf number, and tissue/component mass.
  3. Seedling growth and survival were negatively affected by cotyledon loss regardless of oak species. However, these negative effects decreased as the epicotyl length at which cotyledons were removed increased. We also found that there was a threshold epicotyl length above which seedling survival and performance were relatively unaffected in white oak species compared to red oak species.
  4. Following cotyledon removal, early germinating white oak (section Quercus) seedlings survived and/or grew better than the late germinating red oak (section Lobatae) seedlings. This was likely caused by a difference in dependence on cotyledon reserves, which ultimately affected the ability of seedlings to tolerate cotyledon removal.
  5. Synthesis. From an evolutionary perspective, this is likely to follow from the early germination in white oaks and the ability of seed consumers to locate young seedlings from the emerging epicotyls. Our study has implications for forest regeneration by suggesting additional opportunities for white oak species to establish following epicotyl emergence. Future studies should consider quantifying the rates of post-germination cotyledon loss.


  • Ancillotto, L., T. Notomista, E. Mori, S. Bertolino and D. Russo (2018) Assessment of Detection Methods and Vegetation Associations for Introduced Finlayson’s Squirrels (Callosciurus finlaysonii) in Italy. Environmental Management.

Abstract: Managing biological invasions requires rapid, cost-effective assessments of introduced species’ occurrence, and a good understanding of the species’ vegetation associations. This is particularly true for species that are elusive or may spread rapidly. Finlayson’s squirrel (Callosciurus finlaysonii) is native to Thailand and southeastern Asia, and two introduced populations occur in peninsular Italy. One of the two introduced populations is rapidly expanding, but neither effective monitoring protocols nor reliable information on vegetation associations are available. To fill this gap, we conducted visual surveys and hair tube sampling in a periurban landscape of southern Italy to compare the effectiveness of these two methods in assessing presence of Finlayson’s squirrel. We also determined the species’ association with vegetation types at detection locations and nesting sites. Both visual and hair tube sampling effectively assessed the species’ presence, but hair tubes resulted in fewer false absences. Moreover, when we controlled for the costs of labor and equipment, hair tubes were 33.1% less expensive than visual sampling. Presence of squirrels and their nests was positively correlated with shrub species richness, indicating that the occurrence of forests with well-developed understory may inhibit the spread of the species.

  • Baldwin, M. K. L., Young, N. A., Matrov, D. & Kaas, J. H. (2018) Cortical projections to the superior colliculus in grey squirrels (Sciurus carolinensis). European Journal of Neuroscience 0(0).

Abstract The superior colliculus is an important midbrain structure involved with integrating information from varying sensory modalities and sending motor signals to produce orienting movements towards environmental stimuli. Because of this role, the superior colliculus receives a multitude of sensory inputs from a wide variety of subcortical and cortical structures. Proportionately, the superior colliculus of grey squirrels is among the largest in size of all studied mammals, suggesting the importance of this structure in the behavioural characteristics of grey squirrels. Yet, our understanding of the connections of the superior colliculus in grey squirrels is lacking, especially with respect to possible cortical influences. In this study, we placed anatomical tracer injections within the medial aspect of the superior colliculus of five grey squirrels (Sciurus carolinensis) and analysed the areal distribution of corticotectal projecting cells in flattened cortex. V1 projections to the superior colliculus were studied in two additional animals. Our results indicate that the superior colliculus receives cortical projections from visual, higher order somatosensory, and higher order auditory regions, as well as limbic, retrosplenial and anterior cingulate cortex. Few, if any, corticotectal projections originate from primary motor, primary somatosensory or parietal cortical regions. This distribution of inputs is similar to the distribution of inputs described in other rodents such as rats and mice, yet the lack of inputs from primary somatosensory and motor cortex is features of corticotectal inputs more similar to those observed in tree shrews and primates, possibly reflecting a behavioural shift from somatosensory (vibrissae) to visual navigation.

  • Barbara, F., Morgia, V. L., Parodi, V., Toscano, G. & Venturino, E. (2018) Analysis of the Incidence of Poxvirus on the Dynamics between Red and Grey Squirrels. Mathematics 6(113): 1-21.

Abstract: A model for the interactions of the invasive grey squirrel species as asymptomatic carriers of the poxvirus with the native red squirrel is presented and analyzed. Equilibria of the dynamical system are assessed, and their sensitivity in terms of the ecosystem parameters is investigated through numerical simulations. The findings are in line with both field and theoretical research. The results indicate that mainly the reproduction rate of the alien population should be drastically reduced to repel the invasion, and to achieve disease eradication, actions must be performed to reduce the intraspecific transmission rate; also, the native species mortality plays a role: if grey squirrels are controlled, increasing it may help in the red squirrel preservation, while the invaders vanish; on the contrary, decreasing it in favorable situations, the coexistence of the two species may occur. Preservation or restoration of the native red squirrel requires removal of the grey squirrels or keeping them at low values. Wildlife managers should exert a constant effort to achieve a harsh reduction of the grey squirrel growth rate and to protect the remnant red squirrel population.

  • Cao, L., Wang, B., Yan, C., Wang, Z., Zhang, H., Geng, Y., Chen, J. & Zhang, Z. (2018) Risk of cache pilferage determines hoarding behavior of rodents and seed fate. Behavioral Ecology 29(4): 984-991.

Cache pilferage by competitors is thought to drive the evolution of hoarding behavior in animals, which plays significant roles in tree regeneration and formation of mutualisms between trees and animals. However, little is known how cache pilferage risk among seeds of different tree species or years affects hoarding behavior and seed dispersal by animals. We hypothesized that scatter-hoarding rodents could adjust hoarding behavior according to variation in cache pilferage risk among seeds and years to minimize cache pilferage, by investigating the relationship between cache pilferage risk and seed dispersal of 7 tree species over 3 years in tropical forest in southwest China. Among years, the high pilferage risk was related to high probability of larder-hoarding and short periods of scatter-hoarding; whereas, the probability of scatter-hoarding was higher in intermediate pilferage year than in both low and high pilferage years. Among seeds, high pilferage risk was related to low probability and short periods of scatter-hoarding. Our results indicated that cache pilferage risk significantly affected hoarding behaviors and seed dispersal by scatter-hoarding rodents as well as seed fates. Cache pilferage risk was a reliable explanatory factor for variation in seed dispersal, and it might be an important driving force in the evolution of rodent hoarding behaviors and seed characteristics.

  • Chow, P. K. Y., P. W. W. Lurz and S. E. G. Lea (2018). A battle of wits? Problem-solving abilities in invasive eastern grey squirrels and native Eurasian red squirrels. Animal Behaviour 137: 11-20.

Abstract: Behavioural flexibility has been argued to be an evolutionarily favourable trait that helps invasive species to establish themselves in non-native environments. Few studies, however, have compared the level of flexibility (whether considered as an outcome or as a process) in mammalian invaders and related native species. Here, we tested whether flexibility differs between groups of free-ranging invasive eastern grey squirrels, Sciurus carolinensis, and native Eurasian red squirrels, Sciurus vulgaris, in the U.K., using an easy and a difficult food extraction task. All individuals of both species showed flexibility, at the outcome level, in solving the easy task and solution time was comparable between species across a series of successes. A higher proportion of grey squirrels than red squirrels solved the difficult task. However, for those squirrels that did solve the task, solving efficiency was comparable between species on their first success, and a few red squirrels outperformed the grey squirrels in subsequent successes. Between-species analysis showed that instantaneous flexibility, flexibility at the process level that was measured as the rate of switching between tactics after a failed attempt, was higher in red squirrels than in grey squirrels. Within-species analysis also revealed that red squirrel problem solvers showed higher flexibility at the process level than their nonsolver counterparts. Nonsolvers also failed to make ‘productive’ switches (switching from ineffective to effective tactics). Together, the results suggest that problem-solving ability overlaps in the two species, but is less variable, and on average higher, in grey squirrels than in red squirrels. The superior behavioural flexibility of the grey squirrels, shown here by success at problem solving, may have facilitated their invasion success, but it may also have resulted from selective pressures during the invasion process.

  • Davidson, A. D., Hunter, E. A., Erz, J., Lightfoot, D. C., McCarthy, A. M., Mueller, J. K. & Shoemaker, K. T. (2018) Reintroducing a keystone burrowing rodent to restore an arid North American grassland: challenges and successes. Restoration Ecology 26(5): 909-920.

Prairie dogs (Cynomys spp.) are important ecosystem engineers in North America’s central grasslands, and are a key prey base for numerous predators. Prairie dogs have declined dramatically across their former range, prompting reintroduction efforts to restore their populations and ecosystem functions, but the success of these reintroductions is rarely monitored rigorously. Here, we reintroduced 2,400 Gunnison’s prairie dogs (C. gunnisoni) over a period of 6 years to the Sevilleta National Wildlife Refuge, in central New Mexico, U.S.A., a semi-arid grassland ecosystem at the southern edge of their range. We evaluated the population dynamics of prairie dogs following their reintroduction, and their consequent effects on grassland vertebrates. We found postrelease survival of prairie dogs stabilized at levels typical for the species (ca. 50%) after approximately 1 month, while average annual recruitment was ca. 0.35 juveniles per female, well below what was required for a self-sustaining, stable population. Extreme drought conditions during much of the study period may have contributed to low recruitment. However, recruitment increased steadily over time, indicating that the reintroduced colony may simply need more time to establish in this arid system. We also found well-known associates of prairie dog colonies, such as American badgers (Taxidea taxus) and burrowing owls (Athene cunicularia), were significantly more common on the colonies than off. After 7 years, we have yet to meet our goal of establishing a self-sustaining population of Gunnison’s prairie dogs in this semi-arid grassland. But despite the uncertainty and challenges, our work shows that reestablishing keystone species can promote ecosystem restoration.

  • Desantis, L. M., Bowman, J., Faught, E., Boonstra, R., Vijayan, M. M. & Burness, G. (2018) Corticosteroid-binding globulin levels in North American sciurids: implications for the flying squirrel stress axis. Canadian Journal of Zoology 96(10): 1090-1096.

Corticosteroid-binding globulin (CBG) helps to regulate tissue bioavailability of circulating glucocorticoids (GCs), and in most vertebrates, ≥80%–90% of GCs bind to this protein. New World flying squirrels have higher plasma total cortisol levels (the primary corticosteroid in sciurids) than most vertebrates. Recent research suggests that flying squirrels have either low amounts of CBG or CBG molecules that have a low binding affinity for cortisol, as this taxon appears to exhibit very low proportions of cortisol bound to CBG. To test whether CBG levels have been adjusted over evolutionary time, we assessed the levels of this protein in the plasma of northern (Glaucomys sabrinus (Shaw, 1801)) and southern (Glaucomys volans (Linnaeus, 1758)) flying squirrels using immunoblotting, and compared the relative levels among three phylogenetically related species of sciurids. We also compared the pattern of CBG levels with cortisol levels for the same individuals. Flying squirrels had higher cortisol levels than the other species, but similar levels of CBG to their closest relatives (tree squirrels). We conclude that CBG levels in flying squirrels have not been adjusted over evolutionary time, and thus, the uncoupling of CBG levels from cortisol concentrations may represent an evolutionary modification in the lineage leading to New World flying squirrels.

  • d’Ovidio, D. & Pirrone, F. (2018) A cross-sectional survey to evaluate the pet squirrel population and ownership profiles. Preventive Veterinary Medicine 159: 65-71.

While the presence of squirrels in households is growing, little data is published on their status in captivity. A web-based questionnaire for owners was devised eliciting information about them, their squirrels and their squirrels’ husbandry and health. One hundred owners answered the survey, with most respondents being located in Europe (n = 81). Only data from these respondents were analysed. Twenty-five percents of the owners housed an invasive non-native species of European Union concern (S. carolinensis and T. sibiricus), some of which were younger than three years of age and all but one were sexually intact. This is of particular concern, as the acquisition of these invasive species is illegal since 2015 (European Union Regulation 1143/2014), due to the severe threats they pose to biodiversity. Moreover, escapes derived from improper keeping of intact specimens may augment feral populations or establish new colonies. Among 81 cases, only 5% were neutered, mostly for health reasons. Sixty-three percents of the squirrels had health problems, particularly dermatologic (52%) and intestinal disorders (34%). Most owners reported to visit the veterinarian only if their pet was ill rather than for preventive care. This is the first survey on pet squirrel ownership reported to date. Information that emerges from this study will be useful in implementing rational veterinary strategies for managing pet squirrels properly and, in parallel, meeting the challenges arising from private keeping of alien species.

  • Everest DJ, Shuttleworth CM, Grierson SS, Dastjerdi A, Stidworthy MF, Duff JP, et al. (2018) The implications of significant adenovirus infection in UK captive red squirrel (Sciurus vulgaris) collections: How histological screening can aid applied conservation management. Mammalian Biology 88:123-9.

Abstract: Conservation trans-locations using captive bred red squirrels (Sciurus vulgaris) is increasing in the United Kingdom (UK). However, project managers are often unaware of the risk of pathological adenovirus (ADV) infection. In this study we illuminate the viral threat using transmission electron microscopy (TEM) and polymerase chain reaction (PCR) assays. Both techniques were used to screen samples collected from 26 English and Welsh captive red squirrel collections. Of 181 carcasses received between 2002 and 2016, 129 (71%) were suitable for routine surveillance post mortem examination (PME). A range of tissues were examined with ADV identified from a variety of samples by PCR and TEM in 92 (72%) cases encompassing 23 of the 26 study collections (89%). ADV enteritis was histologically confirmed in two deaths (2%) with another 39 (30%) through both laboratory and clinical findings, considered as likely clinically-significant ADV cases, but advanced autolysis precluded accurate assessment and confirmatory histological diagnosis. Other positive cases were more indicative of sub-clinical infection. Clusters of ADV red squirrel deaths were recorded with circumstantial evidence suggesting inter-collection movement of presumed ADV infected donated animals had triggered mortality in recipient collections. During the study, several collections intermittently experienced ADV-associated deaths. Definitive cause of death was not determined in most cases, but a diverse range of diagnoses were recorded in 25 (19%) animals. Implications of these findings for captive United Kingdom (UK) red squirrel husbandry are discussed. It is recommended that protocols be drawn up to minimise potential intra-species ADV infection and highlight the danger of contact with ADV infected wood mice (Apodemus sylvaticus).

  • Goldstein, E.A., M.J. Merrick & J.L. Koprowski (2018) Low survival, high predation pressure present conservation challenges for an endangered endemic forest mammal. Biological Conservation 221: 67-77.

Abstract: Knowledge of which population parameters and mortality risks contribute most to population decline and endangerment is necessary to develop informed and actionable conservation plans for threatened and endangered species (Rushton et al., 2006). The federally endangered Mount Graham red squirrel (Tamiasciurus fremonti grahamensis) is restricted to the Pinaleño Mountains, in southeastern Arizona, USA. The population is critically threatened with extensive habitat loss from fire as well as by an introduced non-native squirrel species, the Abert’s squirrel (Sciurus aberti). Recovery is challenged by low survival and poor reproduction, such that the subspecies is functionally semelparous. We calculate survival rates and cause-specific mortality hazards from known-fate individuals to understand the impact of predation on survival and demography in this peripheral population. We document the lowest survival and highest rates of mortality in any population of North American red squirrels in both adult and juvenile age classes (mean annual survival: adults = 0.32, juveniles = 0.26). We attributed the majority of confirmed deaths to avian predation (adults 65%, juveniles 75%), and the daily hazard rate for avian predation was 15 times higher than for mammalian predation and 2 times higher than death from unknown causes. It is likely that the presence of an ecologically similar, non-native tree squirrel subsidizes a diverse avian predator guild, which includes two raptor species of conservation concern. In addition to efforts to remove the non-native Abert’s squirrel, we recommend immediate forest restoration efforts in the long term, and habitat augmentation to increase structural complexity, cover, shelter, and food resources in the short term.

  • Hammond, T. T., Palme, R. & Lacey, E. A. (2018) Ecological specialization, variability in activity patterns and response to environmental change. Biology Letters 14(6).

Differences in temporal patterns of activity can modulate the ambient conditions to which organisms are exposed, providing an important mechanism for responding to environmental change. Such differences may be particularly relevant to ecological generalists, which are expected to encounter a wider range of environmental conditions. Here, we compare temporal patterns of activity for partially sympatric populations of a generalist (the lodgepole chipmunk, Tamias speciosus) and a more specialized congener (the alpine chipmunk, Tamias alpinus) that have displayed divergent responses to the past century of environmental change. Although mean activity budgets were similar between species, analyses of individual-level variation in locomotion revealed that T. alpinus exhibited a narrower range of activity patterns than T. speciosus. Further analyses revealed that T. alpinus was more active earlier in the day, when temperatures were cooler, and that activity patterns for both species changed with increased interspecific co-occurrence. These results are consistent with the greater responsiveness of T. alpinus to changes in environmental conditions. In addition to highlighting the utility of accelerometers for collecting behavioural data, our findings add to a growing body of evidence, suggesting that the greater phenotypic variability displayed by ecological generalists may be critical to in situ responses to environmental change.

  • Hanmer, H. J., Thomas, R. L. & Fellowes, M. D. E. (2018) Introduced Grey Squirrels subvert supplementary feeding of suburban wild birds. Landscape and Urban Planning 177: 10-18.

Abstract: Providing food for wild birds is perhaps the most widespread intentional interaction between people and wildlife. In the UK, almost half of households feed wild birds, often as peanuts and seed supplied in hanging feeders. Such food is also taken by the introduced, invasive Grey Squirrel Sciurus carolinensis. Little is known of how Grey Squirrels utilise this resource and how they affect feeder use by wild birds. To assess this we recorded the numbers and time spent by animals visiting experimental feeding stations in suburban gardens, and also asked if exclusionary guards (to prevent Grey Squirrel access), food type (peanut, mixed seed), habitat and weather conditions influenced visits. Using automated cameras, we recorded 24,825 bird and 8577 Grey Squirrel visits. On average >44% of the time feeders were utilised, they were being visited by Grey Squirrels. Grey Squirrel presence prevented birds from feeding at the same time (>99.99%). Feeders where Grey Squirrels were dominant were less likely to be visited by birds, even in their absence. Guards reduced Grey Squirrel use to a minimum on seed feeders, and by approximately half on peanut feeders. Squirrels, food type, guard status, habitat and rainfall all influenced bird activity and timing of feeder visits. Our work suggests that Grey Squirrels reduce the availability of supplementary food to wild birds, while gaining large volumes of food resources with corresponding benefits. Given the ubiquity of supplementary feeding, it is likely that this is an important resource for urban Grey Squirrels; feeder guards mitigate this effect.

  • Lane, J., McAdam, A., McFarlane, E., Williams, C., Humphries, M., Coltman, D., Gorrell, J. & Boutin, S. (2018) Phenological shifts in North American red squirrels: disentangling the roles of phenotypic plasticity and microevolution. Journal of Evolutionary Biology

Abstract: Phenological shifts are the most widely reported ecological responses to climate change, but the requirements to distinguish their causes (i.e., phenotypic plasticity versus microevolution) are rarely met. To do so, we analyzed almost two decades of parturition data from a wild population of North American red squirrels (Tamiasciurus hudsonicus). Although an observed advance in parturition date during the first decade provided putative support for climate change‐driven microevolution, a closer look revealed a more complex pattern. Parturition date was heritable (h2 = 0.14 (0.07 to 0.21 (HPD interval)) and under phenotypic selection (β = ‐0.14 ± 0.06 (SE)) across the full study duration. However, the early advance reversed in the second decade. Further, selection did not act on the genetic contribution to variation in parturition date, and observed changes in predicted breeding values did not exceed those expected due to genetic drift. Instead, individuals responded plastically to environmental variation, and high food (white spruce (Picea gluaca) seed) production in the first decade appears to have produced a plastic advance. In addition, there was little evidence of climate change affecting the advance, as there was neither a significant influence of spring temperature on parturition date or evidence of a change in spring temperatures across the study duration. Heritable traits not responding to selection in accordance with quantitative genetic predictions has long presented a puzzle to evolutionary ecologists. Our results on red squirrels provide empirical support for one potential solution: phenotypic selection arising from an environmental, as opposed to genetic, covariance between the phenotypic trait and annual fitness.

  • Mielke, F., Schunke, V., Wölfer, J. & Nyakatura, J. A. (2018) Motion analysis of non-model organisms using a hierarchical model: Influence of setup enclosure dimensions on gait parameters of Swinhoe’s striped squirrels as a test case. Zoology 129: 35-44.

In in-vivo motion analyses, data from a limited number of subjects and trials is used as proxy for locomotion properties of entire populations, yet the inherent hierarchy of the individual and population level is usually not accounted for. Despite the increasing availability of hierarchical model frameworks for statistical analyses, they have not been applied extensively to comparative motion analysis. As a case study for the use of hierarchical models, we analyzed locomotor parameters of four Swinhoe’s striped squirrels. The small-bodied arboreal mammals exhibit brief bouts of rapid asymmetric gaits. Spatio-temporal parameters on runways with experimentally varied dimensions of the setup enclosure were compared to test for their potentially confounding effects. We applied principal component analysis to evaluate changes to the overall locomotor pattern. A common, non-hierarchical, pooled statistical analysis of the data revealed significant differences in some of the parameters depending on enclosure dimensions. In contrast, we used a hierarchical Bayesian generalized linear model (GLM) that considers subject specific differences and population effects to compare the effect of enclosure dimensions on the measured parameters and the principal components. None of the population effects were confirmed by the hierarchical GLM. The confounding effect of a single subject that deviates in its locomotor behavior is potentially bigger than the influence of the experimental variation in enclosure dimensions. Our findings justify the common practice of researchers to intuitively select an enclosure with dimensions assumed as “non-constraining”. Hierarchical models can easily be designed to cope with limited sample size and bias introduced by deviating behavior of individuals. When limited data is available—a typical restriction of in-vivo motion analyses of non-model organisms—density distributions of the Bayesian GLM used here remain reliable and the hierarchical structure of the model optimally exploits all available information. We provide code to be adjusted to other research questions.

  • Mori, E., Menchetti, M., Zozzoli, R. & Milanesi, P. (2018) The importance of taxonomy in species distribution models at a global scale: the case of an overlooked alien squirrel facing taxonomic revision. Journal of Zoology 0(0).

Abstract The Siberian chipmunk is native to north-eastern Asia, but alien populations of this squirrel, introduced through the pet trade, occur in many European countries. This rodent has been listed as an invasive species of European concern, being a potential vector of ticks spreading Lyme disease. We aimed to assess its current distribution range and to identify areas of potential invasion. Two sets of species distribution models were conducted, one considering the locations of the species (n = 625 occurrences) and the other with only the occurrences of the Korean subspecies (the invasive one in Europe; n = 255 occurrences), which might be a separate species from the Siberian one. We included 19 uncorrelated predictors (two topographic, nine land cover, five bioclimatic and three anthropogenic variables), which may represent the habitat characteristics of the target species. Most of the northern hemisphere supports the establishment of the Siberian chipmunk, particularly for the invasive Korean subspecies (especially in Europe, where it is already established), mostly in urban areas. Anthropogenic food supply was found to be an important factor promoting the growth of alien populations of chipmunks, whereas the presence of the native red squirrel at the time of introduction may limit it.

  • Mori, E., Zozzoli, R. & Menchetti, M. (2018) Global distribution and status of introduced Siberian chipmunks Eutamias sibiricus. Mammal Review 48(2): 139-152.

Abstract: * Among invasive alien species, squirrels are prominent because of their popularity as pets and their positive perception by the general public. In Europe, populations of five alien squirrel species are reported. The pet trade represents a high-risk pathway for the introduction of rodents, which are likely to become invasive because of their reproductive biology and wide native distribution ranges. In the European Union, a trade ban has been imposed on some particularly impacting species, such as the eastern grey squirrel Sciurus carolinensis. Eradication and numerical control is needed for most introduced squirrels in Europe (including the Siberian chipmunk), according to European Union Regulation 1143/2014 on alien species. * We summarise the current distribution of the ground-dwelling Siberian chipmunk Eutamias sibiricus, one of the most common pet squirrels in Europe and Asia, in its invasive range. * Established populations of Siberian chipmunk, in most cases composed of small numbers of individuals, currently occur in France, Switzerland, Italy, Germany, Belgium, the Netherlands, Denmark, and Russia. The species was present in Austria, Sweden, and Hong Kong, and unsuccessful introductions occurred in Spain and the British Isles. The first records from Greece are also reported. Most introductions took place during the 1990s, when individuals were intentionally released (67% of extant populations result from such releases). Population size was correlated with the proximity to urban areas. * Human risk of infection with the agent of Lyme borreliosis seems to be the highest where populations of alien Siberian chipmunk occur. Other impacts have never been reported. Competition with native rodents (e.g. the red squirrel Sciurus vulgaris and dormice, Gliridae) has been speculated on, as well as predation on nests of native warblers (Sylvidae). * Impacts by alien Siberian chipmunks have been overlooked for a long time. Despite this, given that the species may affect native biodiversity and human health, eradication of established populations is recommended.

Pero, E. M. & Hare, J. F. (2018) Costs of Franklin’s ground squirrel (Poliocitellus franklinii) ectoparasitism reveal adaptive sex allocation. Canadian Journal of Zoology 96(6): 585-591.

Parasite infestation may impose direct costs of blood, nutrient, and energy depletion, along with indirect costs of increased immune response upon hosts. We investigated how ectoparasitism influences body mass and reproduction in a free-living population of Franklin’s ground squirrels (Poliocitellus franklinii (Sabine, 1822)) located near Delta Marsh, Manitoba, Canada. We experimentally reduced ectoparasite burden by treating seven reproductive females with an insecticide following breeding and contrasted body mass and reproductive performance of those individuals to seven sham-treated control females. Insecticide-treated dams did not differ from sham-treated dams in body mass, litter size, or juvenile mass, and thus, dam growth and reproduction were not compromised by ectoparasite defense at the infestation levels experienced in this study. However, litter sex ratio differed significantly between insecticide-treated and control females, with a higher proportion of male offspring produced among females with reduced ectoparasite load. Our findings are thus consistent with the Trivers–Willard model for adaptive sex allocation, yet they provide novel comparative insight into how sociality may modulate the expression of adaptive sex allocation among small mammals given the differential payoff associated with the production of high-quality female versus male offspring in more social versus less social species.

  • Pierre-Henri, F., Marie-Ka, T., Christiane, D., Philippe, G., Violaine, N., Emmanuel JP, D. & Laurent, M. (2018) Flightless scaly-tailed squirrels never learned how to fly: A reappraisal of Anomaluridae phylogeny. Zoologica Scripta 0(0).

Anomaluroidea, commonly known as the “scaly-tailed squirrels,” are an emblematic group of tropical African mammals that includes gliding forms. The family Anomaluridae was until recently represented by three genera: the flying scaly-tailed squirrels (Anomalurus), the flying mouse (Idiurus) and the flightless scaly-tailed squirrels (Zenkerella). Idiurus and Zenkerella have long been grouped into the Zenkerellinae subfamily, and Zenkerella was interpreted as a rare case of evolutionary reversal to non-gliding lifestyle. Recent studies have demonstrated that Zenkerella is sister to all other modern anomalurids, and represents in fact the monogeneric family Zenkerellidae. The Anomalurus genus was split into Anomalurus and Anomalurops, but no study has ever considered all Anomalurus species together in a phylogeny to test the status of Anomalurops. Here, we used mitogenomic next-generation sequencing to infer the phylogenetic relationships among all extant anomalurids and to estimate their divergence ages. We found that the arboreal Zenkerella is the sister group of all extant gliding anomalurids (Idiurus and Anomalurus). We confirmed that Anomaluroidea only evolved the gliding adaptation once. A comparison based on morphological traits indicates that Zenkerella harbours several unique morphological features. We propose new morphological characters for the novel classification of modern Anomaluroidea, which includes the families Zenkerellidae and Anomaluridae. Using different calibration schemes, we demonstrated that classical dating methods relying only on mitogenomes provide rather young Miocene estimates between Zenkerellidae and the Anomaluridae. The use of published nuclear genes, internal calibrations and tip dating converged towards an Eocene split between gliding and non-gliding scaly-tailed squirrels, which is in agreement with the African fossil record. Finally, we provide the first exhaustive species-level molecular phylogenetic inference for the genus Anomalurus. We found that Anomalurus beecrofti is the sister group of all other species of Anomalurus and branched off during the Miocene.

  • Romeo, C., McInnes, C. J., Dale, T. D., Shuttleworth, C., Bertolino, S., Wauters, L. A. & Ferrari, N. (2018) Disease, invasions and conservation: no evidence of squirrelpox virus in grey squirrels introduced to Italy. Animal Conservation 0(0).

Abstract Native red squirrels Sciurus vulgaris in Great Britain and Ireland are threatened by alien grey squirrels S. carolinensis through exploitation competition and spillover of squirrelpox virus (SQPV). By accelerating the replacement of red squirrels by the invader, SQPV represents a fundamental factor to consider when planning management and conservation strategies. In mainland Europe, grey squirrels introduced to Italy threaten the survival of the whole continental red squirrel population, but no extensive surveys for SQPV presence have been carried out in the region. We therefore investigated SQPV infection in north Italian grey squirrel populations through a combination of serological and molecular methods. Firstly, we analysed sera from 285 individuals through an enzyme-linked immunosorbent assay (ELISA) to detect antibodies against SQPV. Secondly, a PCR designed to amplify a segment of the G8R SQPV gene was carried out on DNA extracted from swabs and skin tissue samples from a second set of 66 grey squirrels. ELISA tests identified four reactors (1.4%), but the subsequent PCR survey did not detect any SQPV DNA. Based on the low prevalence observed and on PCR results, we believe that the four suspected positives were the result of an ELISA cross-reaction following exposure to another pox virus. Considering sample size and performances of the two methods, confidence of freedom from SQPV resulted above 99.9%. However, because of the severe impact of SQPV on red squirrels, we recommend the implementation of a passive surveillance plan for the early detection of an SQPV emergence in continental Europe.

  • Santicchia, F., Dantzer, B., van Kesteren, F., Palme, R., Martinoli, A., Ferrari, N. & Wauters, A. L. (2018) Stress in biological invasions: introduced invasive grey squirrels increase physiological stress in native Eurasian red squirrels. Journal of Animal Ecology .

Abstract: 1.Invasive alien species can cause extinction of native species through processes including predation, interspecific competition for resources, or disease‐mediated competition. Increases in stress hormones in vertebrates may be associated with these processes and contribute to the decline in survival or reproduction of the native species. 2.Eurasian red squirrels (Sciurus vulgaris) have gone extinct across much of the British Isles and parts of Northern Italy following the introduction of North American invasive grey squirrels (Sciurus carolinensis). We extracted glucocorticoid metabolites from faecal samples to measure whether the presence of the invasive species causes an increase in physiological stress in individuals of the native species. 3.We show that native red squirrels in seven sites where they co‐occurred with invasive grey squirrels had glucocorticoid concentrations that were three times higher than those in five sites without the invasive species. Moreover, in a longitudinal study, stress hormones in native red squirrels increased after colonisation by grey squirrels. When we experimentally reduced the abundance of the invasive grey squirrels, the concentration of faecal glucocorticoid metabolites in co‐occurring red squirrels decreased significantly between pre‐ and post‐removal periods. 4.Hence, we found that the invasive species acts as a stressor which significantly increases the concentrations of glucocorticoids in the native species. 5.Given that sustained elevations in glucocorticoids could reduce body growth and reproductive rate, our results are consistent with previous studies where the co‐occurrence of the invasive grey squirrel was associated with smaller size and lower reproductive output in red squirrels.

  • Selonen, V. & S. Mäkeläinen (2018) Ecology and protection of a flagship species, the Siberian flying squirrel. Hystrix, the Italian Journal of Mammalogy 2018. 28(2).

Abstract: Having clear ecological knowledge of protected species is essential for being able to successfully take actions towards conservation, but this knowledge is also crucial for managing and preventing conservation conflicts. For example, the Siberian flying squirrel, Pteromys volans , listed in the EU Habitats Directive and inhabiting mature forests that are also the target for logging, has had a major role in political discussions regarding conservation in Finland. This species has also been well-researched during recent decades, providing knowledge on the ecology and management of the animal. Herein, we review knowledge on habitats, demography, community interactions and spatial ecology of this flagship species. We compare the ecology of flying squirrels with that of other arboreal squirrels, and summarize conservation management and policy related to flying squirrels. Reviewed research on the Siberian flying squirrel shows that the species has many similarities in behaviour to other arboreal squirrels. For instance, arboreal squirrels deviate from the general pattern of male-biased sexual size dimorphism in mammals, which perhaps relates to the mating system of arboreal squirrels. Important differences are found in the response of Siberian flying squirrels to tree mast, i.e. pulsed food resource, compared to that of red squirrels, and in communal nesting behaviour compared to that of North American flying squirrels. The extensive knowledge on dispersal behaviour of the flying squirrel, well-studied habitat associations and the proved need for evidence-based conservation may guide researchers and managers working with other similar species. For conservation, the case of the Siberian flying squirrel demonstrates that habitat protection becomes both ineffective and uneconomical if ecological knowledge is not applied in the conservation planning process. The cost-effective conservation of the species requires both landscape-level conservation planning and flexible conservation options to increase the motivation of land owners for conservation.

  • Sheehy E, Sutherland C, O’Reilly C, Lambin X. (2018) The enemy of my enemy is my friend: native pine marten recovery reverses the decline of the red squirrel by suppressing grey squirrel populations. Proceedings of the Royal Society B: Biological Sciences 285(1874).

Abstract: Shared enemies may instigate or modify competitive interactions between species. The dis-equilibrium caused by non-native species introductions has revealed that the outcome of such indirect interactions can often be dramatic. However, studies of enemy-mediated competition mostly consider the impact of a single enemy, despite species being embedded in complex networks of interactions. Here, we demonstrate that native red and invasive grey squirrels in Britain, two terrestrial species linked by resource and disease-mediated apparent competition, are also now linked by a second enemy-mediated relationship involving a shared native predator recovering from historical persecution, the European pine marten. Through combining spatial capture–recapture techniques to estimate pine marten density, and squirrel site-occupancy data, we find that the impact of exposure to predation is highly asymmetrical, with non-native grey squirrel occupancy strongly negatively affected by exposure to pine martens. By contrast, exposure to pine marten predation has an indirect positive effect on red squirrel populations. Pine marten predation thus reverses the well-documented outcome of resource and apparent competition between red and grey squirrels.

Shirkorshidi, M. & Tonkin, M. (2018) Saving Scotland’s Red Squirrels Results of Spring 2017 Squirrel Surveys. Saving Scotland’s Red Squirrels.

Abstract: We present the results of Saving Scotland’s Red Squirrels’ (SSRS) Spring 2017 surveys of red and grey squirrels and compare them with the Spring 2011 and 2012 surveys for the north of Scotland and Spring 2013 for the south of Scotland. We also present the results of additional intensive grey squirrel detection surveys in North East Scotland. Overall, we see a picture of red squirrels maintaining or increasing their occurrence since the beginning of the surveys, but a mixed picture for the occurrence of grey squirrels: a positive change towards decreased grey squirrel range for the northern half of Scotland contrasts with expanding grey squirrel distribution in South Scotland. Taking the regions in turn, the evidence supports a statistically significant increase in red squirrel distribution and a significant decline in grey squirrels in the North East, particularly in areas close to the City of Aberdeen. Across the Highland Line the trend shows a stabilisation of red squirrel occurrence in survey areas, and grey squirrel occurrence limited to the significantly reduced range when compared with the tetrads in 2011 and 2012 Thus we have been successful in preventing incursion of grey squirrels into Scotland’s core red squirrel populations to the north of the Highland Line and protecting. In the south of Scotland, overall, grey squirrel occupancy is shown to have increased since 2014, especially in Berwickshire, where red squirrels are now seldom seen, and, more worryingly, in Dumfriesshire between Thornhill and New Galloway. We believe this to be associated with an exceptional masting year in the autumn of 2014, when there was a superabundance of beech nuts. This led to increased over-winter survival and a peak in production of grey squirrels in 2015, which was evident in our 2015 trapping figures as a surge in grey squirrel numbers right across the country. Despite this, red squirrels appear to have maintained their range and even slightly expanded their occupancy in South Scotland, although the change is not statistically significant.

  • Shuttleworth, C. & Halliwell, E. (2018) Red Squirrels In My Garden. European Squirrel Initiative, Stoneleigh Park, Warwickshire, CV8 2LG England: 120 pp.
  • Starkey, A. & delBarco-Trillo, J. (2018) Vienna Supplementary feeding can attract red squirrels (Sciurus vulgaris) to optimal environments. Mammalian Biology

Abstract: A number of conservation approaches are used to manage threatened species. However, some of these approaches require intensive planning and can often be restricted by funding. Supplementary feeding is a non-invasive and cost-effective approach to manage vulnerable populations, but we lack data on its usefulness. Here we investigated the effects of supplementary feeding on a population of red squirrels (Sciurus vulgaris), a UK priority species which faces competition from the non-native grey squirrel (Sciurus carolinensis). The study took place October-December 2015, lasting 8 weeks. Twenty feeders were installed 1 week prior to the beginning of the study in a protected woodland free from grey squirrels, either containing food (full feeders) or no food (empty feeders), and squirrel abundance before and after feeding was recorded at each feeder (for a total of 27 feeding and recording events). Six times more squirrels were seen at full feeders, and numbers increased by 7 fold after feeding. We also observed that the activity of red squirrels in the vicinity of full feeders increased during the course of the study. Eighty-five hair samples were collected during the study, all of which were found at full feeders. Results demonstrate red squirrels can differentiate between full and empty feeders, suggesting their awareness increases when supplementary food is present. Increased abundance of squirrels at full feeders after feeding times not only implies that squirrels are attracted to and can benefit by supplementation, it also shows that food supplementation can be used to regulate the movement of individuals across habitats. Understanding how red squirrel populations are affected by supplementary feeding will contribute towards existing conservation efforts to improve this species future survival.

  • Stuart, K. D., Vander Haegen, W. M., Jenkins, K. J., Keren, I. N. & West, S. D. (2018) Western gray squirrel resource selection related to fire fuel management. The Journal of Wildlife Management 0(0).

Abstract: One of 3 populations of the state-threatened western gray squirrel (Sciurus griseus) in Washington occurs in the northern Cascade Range (i.e., North Cascades), where long-term fire suppression has increased the risk of catastrophic wildfire. Land management agencies throughout this region have implemented fire fuel reduction programs that alter squirrel habitat and may affect their populations. From April 2008 to September 2011, we investigated resource selection of 38 radio-collared western gray squirrels at 2 study sites in the North Cascades following fire fuel management activities including mechanical thinning and prescribed burning. We developed conditional logistic models to examine resource selection at 3 spatial scales: nest trees, nest sites, and core areas within home ranges. The odds of a squirrel selecting a tree for nesting increased with dwarf mistletoe (Arceuthobium spp.) presence, greater number of surrounding trees with interlocking branches, and tree size. Squirrels selected nest sites that had greater canopy cover, tree connectivity, and presence of dwarf mistletoe than available, unused sites. Core-use areas within home ranges had greater canopy cover, a greater number of tree species, and trees with higher live crowns compared to low-use areas. Our results indicate that fire fuel treatments may negatively affect western gray squirrel habitat across multiple spatial scales. Most variables that were positively related to habitat selection are specifically targeted for reduction in fire fuel management plans and were lower in sampled treated areas compared to untreated areas within the study sites. Key considerations in designing fuel reduction programs that benefit both squirrel habitat conservation and fire fuel management include maintaining forest patches with suitable canopy cover and connectivity, retaining large trees of a mix of species, and allowing for mistletoe infection at a reduced rate. © 2018 The Wildlife Society.

  • Tamura, N., Boonkhaw, P., Prayoon, U., Kanchanasaka, B. & Hayashi, F. (2018) Mating calls are a sensitive indicator of phylogenetic relationships in Callosciurus, tropical tree squirrels. Mammalian Biology.

Abstract: Vocal communication plays an important role in the mating behaviour of arboreal squirrels. Callosciurus is a genus of tree squirrels that includes 15 species distributed in Southeast Asia, and congeneric species often inhabit the same forest. As closely related species of Callosciurus have the potential to interbreed, species recognition from mating calls may be a fundamental reproductive barrier. We compared seven acoustic characteristics of male mating calls in six Callosciurus species and estimated whether the species differences were clear enough to function as a cue. Discriminant function analyses (DFA) classified 87.4% of mating calls to the correct species. All of the calls by C. notatus, C. nigrovittatus and C. caniceps, and 88% of the calls by C. prevostii, were assigned to the correct species, while the percentage of correct classifications was lower in C. finlaysonii (71%) and C. erythraeus (63%). We compared these results with the genetic relationships to determine whether interspecific acoustic differences are caused by adaptive selection (habitat selection and body size) or by a stochastic process (drift). The genetic relationships among the six species were coincident with the differences in mating calls, which supports the stochastic divergence. Species-specific mating calls may be a useful cue for species recognition in Callosciurus, and thus these calls could be an effective trait for phylogenetic analysis in Callosciurus.

  • Thomas, L. S., Teich, E., Dausmann, K., Reher, S. & Turner, J. M. (2018) Degree of urbanisation affects Eurasian red squirrel activity patterns. Hystrix, the Italian Journal of Mammalogy 29(2): 175-180.

With cities growing at a rapid pace, animal species must either retreat to patches of intact natural habitat or adapt to novel conditions in urban areas. While this disturbance causes most species to be in local decline, some show specific behavioural plasticity, facilitating success in a new habitat. The Eurasian red squirrel ( Sciurus vulgaris ) is a common small mammal species which occurs in high numbers in urban environments. To determine which characteristics enable its success, we investigated space use and activity budgets of seven free-ranging individuals living in semi-natural and urban habitats within a large city. We did not find significant differences in animals’ space use between habitat types but tendencies towards smaller home ranges and increased home range overlap existed among individuals in the urban site. Squirrels differed between sites in both overall activity levels and temporal activity patterns: urban animals spent less time active and activity onset was later compared to semi-natural conspecifics. This is likely explained by a combination of dense and reliable supplementary food sources in the urban habitat, reducing foraging effort, and restrictions to movement imposed by higher fragmentation. Flexibility in space use and activity budgets, as well as the ability to exploit anthropogenic food sources and tolerate reduced habitat connectivity, are likely the most important factors contributing to the squirrels’ success in cities. Accordingly, these traits could be used as indicators of low sensitivity towards urbanisation when assessing other species’ potential resilience. However, they do not immunise squirrels against extirpation. Further research on individuals’ foraging ecology and population health may reveal possible threats to urban red squirrels and help predict their future persistence in this challenging habitat.

  • Turkia, T., Selonen, V., Danilov, P., Kurhinen, J., Ovaskainen, O., Rintala, J. & Brommer, J. E. (2018) Red squirrels decline in abundance in the boreal forests of Finland and NW Russia. Ecography 41(8): 1370-1379.

Abstract: Recent global warming and other anthropogenic changes have caused well-documented range shifts and population declines in many species over a large spatial extent. Most large-scale studies focus on birds, large mammals, and threatened species, whereas large-scale population trends of small to medium-sized mammals and species that are currently of least concern remain poorly studied. Large-scale studies are needed because on a smaller scale, important patterns may be masked by local variation and stochastic processes. Here, we utilized snow track census data from Finland and NW Russia to estimate population growth rates of the Eurasian red squirrel Sciurus vulgaris for a period of 17 yr in an area of over 1 000 000 km2. We also studied the effects of changes in summer and winter temperatures, winter precipitation, predator abundance, and canopy cover on estimated red squirrel population growth rates. Our results suggest that red squirrel populations have declined in most parts of the study area, the only remarkable exception being SW Russia. These results are in concordance with previous studies suggesting that species that are still common and of least concern may be declining. However, our findings are in contrast to the common pattern of northern populations of boreal species increasing due to global warming. The estimated population growth rates are in synchrony over vast areas, suggesting that the underlying reasons also operate on a large scale. We indeed find that the population growth rate was lower in regions where winters warmed faster during the study period, suggesting that changes in the environment (or biotic changes associated with it) are linked with the decline of red squirrels.

  • Vander Haegen, W.M., et al., (2018) Endemic diseases affect population dynamics of tree squirrels in contrasting landscapes. The Journal of Wildlife Management 82(2):  328-343.

Abstract: Habitat loss and fragmentation can have detrimental effects on wildlife populations and where pervasive can create population isolates that may experience reduced genetic diversity and lower persistence. Diseases that cause epizootics also can reduce wildlife populations and may have disproportionate effects on small populations. We studied survival of radio-marked western gray squirrels (Sciurus griseus) using known-fate models in Program MARK and we quantified annual reproductive success by following females through the breeding season and counting young at natal nests. We used data on survival and productivity to model population growth rate and associated parameters using deterministic and stochastic approaches. Populations of western gray squirrels that we studied in an extensive, forested landscape and in a highly fragmented, urbanizing landscape in Washington, USA differed in their modeled growth rate. Adult survival was similar between populations although both were strongly affected by different endemic diseases with high epizootic potential. The demographic parameters that differed most between these 2 populations were related to productivity; litter size was marginally smaller and reproductive success was significantly lower in the urbanizing Puget Trough compared to rural Klickitat County. Results of our demographic modeling suggest that the larger Klickitat population is robust to immediate threats, whereas the smaller Puget Trough population is at risk because of its small size and low fecundity. Periodic outbreaks of notoedric mange in the Klickitat population reduce adult survival, although our models suggest that these epizootics would need to occur more frequently than observed to be of significant risk to the population. Continued degradation and fragmentation of western gray squirrel habitat in the Klickitat region along with mild winters resulting from climate change could increase the frequency and severity of mange epizootics and further threaten this population. Actions to retain and improve habitat resources may help ameliorate the effects of future mange epizootics and maintaining quality habitat should be a management priority in this region. The insular Puget Trough population experienced mortality due to tularemia each year of our study with infection rates ≥14%. Lack of characteristic histological indications in some affected squirrels may lead to underreporting of tularemia in animals submitted for routine necropsy and could complicate assessment of mortality risks in wildlife population studies. Given its small size and isolation, the Puget Trough population should be monitored closely for indications of decline in number or occupancy; this small population may need periodic augmentation to maintain genetic diversity. Increasing suitable habitat and maintaining connectivity between currently occupied range and potential habitat in the surrounding landscape will be crucial to the long-term viability of this population but will be challenging in the urbanizing landscape of the Puget Trough.

  • Wells, C. P. & Van Vuren, D. H. (2018) Developmental and social constraints on early reproduction in an asocial ground squirrel. Journal of Zoology 306(1): 28-35.

Abstract: For short-lived species, selection for early reproduction should be strong, yet females often delay their first reproductive bout. Delay in age of first reproduction due to developmental constraints, such as food availability, or social constraints, such as the inhibitory presence of breeding adults, has been documented for social mammals, but effects on asocial species are less well known. We evaluated the influence of developmental and social factors on early reproduction in a short-lived, asocial species, the golden-mantled ground squirrel (Callospermophilus lateralis). We found that females who reproduced as yearlings had been weaned earlier in their natal summer and experienced early snow melt during their yearling spring, suggesting the importance of access to high-quality food at critical stages. Females were more likely to reproduce as yearlings when there were more adult males present during the breeding season, possibly because exposure to males accelerates reproductive maturity. Maternal presence had no effect on yearling reproduction, but yearlings with a littermate sister present were only 22% as likely to reproduce as females without a sister present, suggesting the effect of sibling competition well past weaning. Furthermore, the negative effect of a sister’s presence, but not the presence of other females, suggests that relatedness affects reproductive competition in this asocial species.

  • Wishart, A. E., Williams, C. T., McAdam, A. G., Boutin, S., Dantzer, B., Humphries, M. M., Coltman, D. W. & Lane, J. E. (2018) Is biasing offspring sex ratio adaptive? A test of Fisher’s principle across multiple generations of a wild mammal in a fluctuating environment. Proceedings of the Royal Society B: Biological Sciences 285(1891).

Fisher’s principle explains that population sex ratio in sexually reproducing organisms is maintained at 1 : 1 owing to negative frequency-dependent selection, such that individuals of the rare sex realize greater reproductive opportunity than individuals of the more common sex until equilibrium is reached. If biasing offspring sex ratio towards the rare sex is adaptive, individuals that do so should have more grandoffspring. In a wild population of North American red squirrels (Tamiasciurus hudsonicus) that experiences fluctuations in resource abundance and population density, we show that overall across 26 years, the secondary sex ratio was 1 : 1; however, stretches of years during which adult sex ratio was biased did not yield offspring sex ratios biased towards the rare sex. Females that had litters biased towards the rare sex did not have more grandoffspring. Critically, the adult sex ratio was not temporally autocorrelated across years, thus the population sex ratio experienced by parents was independent of the population sex ratio experienced by their offspring at their primiparity. Expected fitness benefits of biasing offspring sex ratio may be masked or negated by fluctuating environments across years, which limit the predictive value of the current sex ratio.

  • Zozzoli, R., Menchetti, M. & Mori, E. (2018) Spatial behaviour of an overlooked alien squirrel: The case of Siberian chipmunks Eutamias sibiricus. Behavioural Processes 153: 107-111.

Abstract: Alien species of concern within the European Union have been recently listed and their populations need to be monitored, to plan addressed eradication or control programs. Therefore, the assessment of their presence should be rapidly carried out, particularly for elusive species or for those living at low densities. The Siberian chipmunk Eutamias sibiricus is a ground-dwelling squirrel, naturally distributed in northern and eastern Asia. Many introduced populations occur in Europe and Italy too. This species has been listed within the invasive species concern within the European Union and, thus, monitoring is mandatory to manage its potential range expansion. We carried out a hair-tube survey on 31 wood patches in northern and central Italy, where reproductive populations of Siberian chipmunk have been recorded. Hair tubes provided reliable data in assessing the presence of the Siberian chipmunk, with only 1% pseudo-absence and a high detection probability. The occurrence of Siberian chipmunk was positively influenced by study site and by the distance from release site, confirming low dispersal abilities by this species. Dense understorey also affected the presence of chipmunks, preventing them to search for food on the ground and to dig burrows.

  • Zwolak, R. (2018) How intraspecific variation in seed-dispersing animals matters for plants. Biological Reviews 93(2): 897-913.

Abstract: Seed dispersal by animals is a complex phenomenon, characterized by multiple mechanisms and variable outcomes. Most researchers approach this complexity by analysing context-dependency in seed dispersal and investigating extrinsic factors that might influence interactions between plants and seed dispersers. Intrinsic traits of seed dispersers provide an alternative way of making sense of the enormous variation in seed fates. I review causes of intraspecific variability in frugivorous and granivorous animals, discuss their effects on seed dispersal, and outline likely consequences for plant populations and communities. Sources of individual variation in seed-dispersing animals include sexual dimorphism, changes associated with growth and ageing, individual specialization, and animal personalities. Sexual dimorphism of seed-dispersing animals influences seed fate through diverse mechanisms that range from effects caused by sex-specific differences in body size, to influences of male versus female cognitive functions. These differences affect the type of seed treatment (e.g. dispersal versus predation), the number of dispersed seeds, distance of seed dispersal, and likelihood that seeds are left in favourable sites for seeds or seedlings. The best-documented consequences of individual differences associated with growth and ageing involve quantity of dispersed seeds and the quality of seed treatment in the mouth and gut. Individual specialization on different resources affects the number of dispersed plant species, and therefore the connectivity and architecture of seed-dispersal networks. Animal personalities might play an important role in shaping interactions between plants and dispersers of their seeds, yet their potential in this regard remains overlooked. In general, intraspecific variation in seed-dispersing animals often influences plants through effects of these individual differences on the movement ecology of the dispersers. Two conditions are necessary for individual variation to exert a strong influence on seed dispersal. First, the individual differences in traits should translate into differences in crucial characteristics of seed dispersal. Second, individual variation is more likely to be important when the proportions of particular types of individuals fluctuate strongly in a population or vary across space; when proportions are static, it is less likely that intraspecific differences will be responsible for changes in the dynamics and outcomes of plant–animal interactions. In conclusion, focusing on variation among foraging animals rather than on species averages might bring new, mechanistic insights to the phenomenon of seed dispersal. While this shift in perspective is unlikely to replace the traditional approach (based on the assumption that all important variation occurs among species), it provides a complementary alternative to decipher the enormous variation observed in animal-mediated seed dispersal.


  • Amasifuén, C. & E. Heymann (2016) Toucan predation attempt on a Neotropical pygmy squirrel. Mammalia 81: 527.

Abstract: Predation on arboreal squirrels is rarely observed directly. Here we report the observation of a predatory attack on a Neotropical pygmy squirrel, Sciurillus pusillus (É. Geoffroy Saint-Hilaire, 1803), by a white-throated toucan, Ramphastos tucanos, from north-eastern Peruvian Amazonia. The toucan plucked the squirrel from a trunk at ca. 8 m height in flight and then slammed the individual against a liana in an apparent attempt to kill the prey item. This is the first field observation on a predation attempt on S. pusillus, and adds further evidence for predatory habits in toucans.

  • Boonkhaw, P., Prayoon, U., Kanchanasaka, B., Hayashi, F., & Tamura, N. (2017) Colour polymorphism and genetic relationships among twelve subspecies of Callosciurus finlaysonii in Thailand. Mammalian Biology – Zeitschrift für Säugetierkunde.

Abstract: Finlayson’s squirrel (Callosciurus finlaysonii) is distributed in lowland forests in Southeast Asia. The pelage colour is conspicuously polymorphic, and 16 subspecies have been described based on pelage colour patterns. Among them, 12 subspecies are distributed in Thailand, of which 7 are on the mainland and 5 are on islands. In addition, the distribution range of another closely related species, Pallas’s squirrel (Callosciurus erythraeus), overlaps the range of C. finlaysonii in western Thailand. In this study, phylogenetic analysis based on mitochondrial DNA suggested that C. finlaysonii and C. erythraeus did not form separate monophyletic groups. This C. finlaysonii/C. erythraeus complex in Thailand consisted of seven divergent groups, some of which may have arisen from isolation due to large rivers and seas: (1) C. f. nox/cinnamomeus, (2) C. f. finlaysonii/folletti/trotteri, (3) C. f. menamicus, (4) C. erythraeus, (5) C. f. annellatus, (6) C. f. bocourti/boonsongi/floweri, and (7) C. f. frandseni/albivexilli. Pelage colour did not consistently correspond to these genetic groups, suggesting that specific colours may have been acquired multiple times or the genes associated with colour may have variations and polymorphisms within subspecies. Several small populations in the lowlands and on small islands had lower genetic diversity. To conserve the local genetic diversity of C. finlaysonii, it may be necessary to enact legal restrictions on their trade and hunting.

  • Bosch, S., P. W. W. Lurz, et al. (2017). “Nachweis eines neuen Squirrel-Adenovirus bei einem Krankheitsausbruch bei Eichhörnchen (Sciurus vulgaris) in Deutschland 2013 – 2016.  Detection of a new Squirrel-Adenovirus in a disease outbreak in German red squirrels 2013 – 2016 (in German).” Mitteilungen aus unserer Säugetierwelt 20:  27-35.

Summary: 2015 und 2016 kam  es bei wildlebenden Eichhörnchen zu einem großflächigen Krankheits- ausbruch mit
gehäuften Todesfällen in elf Bundesländern in Deutschland. Betroffen waren sowohl junge als auch erwachsene Eichhörnchen. Von den in Pflegestationen eingelieferten Tieren verstarben 161 und nur 24 überlebten. Kranke Tiere litten an zwei unterschiedlichen Symptomkomplexen: schwerer Durchfall oder schwere Atemnot. Bei den Tieren des aktuel- len  Ausbruches wurden  Adenoviren  nachgewiesen. Adenovirus-Infektionen  sind  bei  an schwerem Durchfall leidenden Eichhörnchen von Ausbrüchen in Großbritannien bekannt, wo in den Jahren 2005-2008 in Wales örtlich hohe Sterberaten beobachtet wurden.  Darüber hinaus gelang der histologische Nachweis von Darmparasiten und der kulturelle Nachweis mehrerer  bakterieller Erreger aus Lungen-, Leber- und Darmgewebe. Einige dieser Erreger sind in der  Lage, insbesondere bei  geschwächten,  immunkompromittierten  Tieren  eine schwere Infektion mit Todesfolge hervorzurufen. Zur Abklärung  der Frage, inwieweit die Erreger an der Erkrankung der Tiere beteiligt sind, sind weitere Untersuchungen erforderlich. In keinem der bisher
untersuchten Eichhörnchen aus Deutschland und Großbritannien wur- de ein Hinweis auf das zoonotische VSBV-1 gefunden.

  • Brady Matthew, J., Koprowski John, L., Gwinn, R. N., Jo, Y.-S., & Young, K. (2017) Eastern fox squirrel (Sciurus niger, Linnaeus 1758) introduction to the Sonoran Desert. Mammalia 81: 221. doi:10.1515/mammalia-2015-0162.

Abstract: The eastern fox squirrel, native to the eastern and midwestern United States, was recently documented in the Sonoran Desert in the vicinity of Yuma, Arizona, constituting the first state record for this species. We surveyedthe people of Yuma to determine when and how the squirrels arrived. The squirrels were first observed in the 1960s, but may have been resident for a longer period. Since the 1960s, squirrels have spread throughout the city limits and extended south ~15 km into Somerton, Arizona. How the squirrels arrived is not clear, but must be the result of an introduction, as no nearby populations exist. The persistence of eastern fox squirrels in this unique habitat is due to synanthropic relationships.

  • Brommer, J.E., Wistbacka, R. & Selonen, V.  (2017) Immigration ensures population survival in the Siberian flying squirrel. Ecology and Evolution 7: 1858-1868.

Abstract: Linking dispersal to population growth remains a challenging task and is a major knowledge gap, for example, for conservation management. We studied relative roles of different demographic rates behind population growth in Siberian flying squirrels in two nest-box breeding populations in western Finland. Adults and offspring were captured and individually identifiable. We constructed an integrated population model, which estimated all relevant annual demographic rates (birth, local [apparent] survival, and immigration) as well as population growth rates. One population (studied 2002–2014) fluctuated around a steady-state equilibrium, whereas the other (studied 1995–2014) showed a numerical decline. Immigration was the demographic rate which showed clear correlations to annual population growth rates in both populations. Population growth rate was density dependent in both populations. None of the demographic rates nor the population growth rate correlated across the two study populations, despite their proximity suggesting that factors regulating the dynamics are determined locally. We conclude that flying squirrels may persist in a network of uncoupled subpopulations, where movement between subpopulations is of critical importance. Our study supports the view that dispersal has the key role in population survival of a small forest rodent.

  • Chavel, E. E., Mazerolle, M. J., Imbeau, L., & Drapeau, P. (2017) Comparative evaluation of three sampling methods to estimate detection probability of American red squirrels (Tamiasciurus hudsonicus). Mammalian Biology – Zeitschrift für Säugetierkunde 83: 1-9.

Abstract:  Measuring changes in species distribution and understanding factors influencing site occupancy are recurring goals in wildlife studies. Imperfect detection of species hinders such studies, resulting in the underestimation of the number of sites occupied by the species of interest. American red squirrels (Tamiasciurus hudsonicus) are sampled traditionally with live-traps that require substantial resources to deploy and monitor. Here, we assessed whether auditory methods yield similar detection probabilities. We compared the detection probability of American red squirrels in boreal forest using point counts, playback counts, and live-trapping. Over the summer of 2014, we conducted three trapping sessions in 60 sites within black spruce forests of northwestern Quebec, Canada. We also conducted 10 min point counts in the same sites, together with playback counts using recordings of American red squirrel alarm and territorial calls. Using dynamic occupancy models to analyse three primary periods, all composed of three secondary periods, we found that the detection probability of squirrels from point counts was as high as with live-trapping. Our results thus highlight the value of the point count method in measuring American red squirrel occupancy.

  • Cooper, Eve B., Taylor, Ryan W., Kelley, Amanda D., Martinig, April R., Boutin, S., Humphries, Murray M., Dantzer, B., Lane, Jeffrey E. & McAdam, Andrew G. (2017) Personality is correlated with natal dispersal in North American red squirrels. Behaviour 154(9-10): 939-961.

Individual natal dispersal behaviour is often difficult to predict as it can be influenced by multiple extrinsic and intrinsic factors. Individual differences in personality have been shown to be an important correlate of dispersal behaviour. However, the relationships between personality traits and dispersal are often inconsistent within and across studies and the causes of these discrepancies are often unknown. Here we sought to determine how individual differences in activity and aggression, as measured in an open-field trial, were related to natal dispersal distance in a wild population of North American red squirrels (Tamiasciurus hudsonicus). For 14 cohorts, while individual aggression consistently had no association with dispersal distance, the association between activity and dispersal fluctuated through time, mediated by population density. The environmental-dependence of the relationship between personality and dispersal in this population is indicative of the importance of considering external conditions when predicting dispersal behaviour.

  • Everest, D., Floyd, T., Donnachie, B., Irvine, R., Holmes, J., & Shuttleworth, C. (2017). Confirmation of squirrelpox in Welsh red squirrels. Veterinary Record 181: 514-515.
  • Fisher, D. N., Boutin, S., Dantzer, B., Humphries, M. M., Lane, J. E., & McAdam, A. G. Multilevel and sex-specific selection on competitive traits in North American red squirrels. Evolution n/a-n/a. doi:10.1111/evo.13270.

Abstract: Individuals often interact more closely with some members of the population (e.g. offspring, siblings or group members) than they do with other individuals. This structuring of interactions can lead to multilevel natural selection, where traits expressed at the group-level influence fitness alongside individual-level traits. Such multilevel selection can alter evolutionary trajectories, yet is rarely quantified in the wild, especially for species that do not interact in clearly demarcated groups. We quantified multilevel natural selection on two traits, postnatal growth rate and birth date, in a population of North American red squirrels (Tamiasciurus hudsonicus). The strongest level of selection was typically within-acoustic social neighbourhoods (within 130m of the nest), where growing faster and being born earlier than nearby litters was key, while selection on growth rate was also apparent both within-litters and within-study areas. Higher population densities increased the strength of selection for earlier breeding, but did not influence selection on growth rates. Females experienced especially strong selection on growth rate at the within-litter level, possibly linked to the biased bequeathal of the maternal territory to daughters. Our results demonstrate the importance of considering multilevel and sex-specific selection in wild species, including those that are territorial and sexually monomorphic.

  • Haigh A, Butler F, O’Riordan R, Palme R  (2017) Managed parks as a refuge for the threatened red squirrel (Sciurus vulgaris) in light of human disturbance. Biological Conservation 211 Part A: 29-36.

Abstract: As the invasive grey squirrel continues to spread, red squirrels are dying out. The result may be isolated populations in managed parks, where access can be controlled. However, recreation can often have a negative effect on wildlife, reducing the conservation potential of parks. Fota Wildlife Park receives over 300,000 visitors each year and is located on an island that is currently free of grey squirrels. We examined the effect of visitors on the existing red squirrel population. Sampling was conducted in the presence and absence of the public. Ten trapping sessions took place from March 2013 to 2014 and faeces were collected to examine stress levels. Squirrels were observed to concentrate their activity in non-public areas and move into public areas when the park was closed. Radio tracked squirrels, from the adjacent gardens (intermediate disturbance), also used habitats in the wildlife park (high disturbance) when it was closed but returned when the park had opened. When squirrels were observed in public areas, visitors were only visible on 15% of occasions. Levels of faecal cortisol metabolites (FCM) were highest in areas where human disturbance was greatest. However, there was no correlation between visitor numbers and the stress levels of squirrels. FCM levels were however, positively correlated with density of squirrels. The fact that high numbers of squirrels continued to utilise the wildlife park demonstrates that managed parks could provide an important reserve for the maintenance of the species, as long as non-public areas are accessible.

  • Hoset, K. S., Villers, A., Wistbacka, R., & Selonen, V. (2017) Pulsed food resources, but not forest cover, determines lifetime reproductive success in a forest-dwelling rodent. Journal of Animal Ecology n/a-n/a. doi:10.1111/1365-2656.12715.

Abstract: 1.The relative contributions of habitat and food availability on fitness may provide evidence for key habitat features needed to safeguard population persistence. However, defining habitat quality for a species can be a complex task, especially if knowledge on the relationship between individual performance and habitat quality is lacking. 2.Here, we determined the relative importance of availability of suitable forest habitat, body mass, and food from masting tree species on female lifetime reproductive success (LRS) of Siberian flying squirrels (Pteromys volans). 3.We calculated LRS of 500 female flying squirrels based on a 22 year-long longitudinal data set of two populations from western Finland. We assessed with generalised additive models the potential effects of availability of suitable habitat and cumulative lifetime availability of food from masting tree species on female LRS, longevity and fecundity. On a reduced dataset, we evaluated the importance of female winter body mass and conducted a piecewise path analysis to determine how variables were connected. 4.According to generalised additive models female longevity, fecundity and LRS were mainly determined by variation in cumulative lifetime availability of food from masting alder and birch. Instead, habitat and body mass had smaller role. The path analysis indicated that lifetime food availability had direct effect on longevity and fecundity, and these had equal effect on LRS at both study sites. 5.Our results on LRS shows that the occurrence of tree masting events during a flying squirrel female’s lifetime have profoundly larger effect on lifetime reproductive success than the cover of suitable forest habitat. Furthermore, this study emphasises the importance of both fecundity and longevity, and the indirect effects of food availability via those components, as determinants of lifetime fitness of female flying squirrels.

  • Inskip, S., Taylor, G. M., Anderson, S., & Stewart, G. (2017). Leprosy in pre-Norman Suffolk, UK: biomolecular and geochemical analysis of the woman from Hoxne. Journal of Medical Microbiology 66(11): 1640-1649. doi:doi:10.1099/jmm.0.000606

Abstract: PURPOSE: A woman’s skull, exhibiting features of lepromatous leprosy (LL), was recovered from a garden in Hoxne, Suffolk. The absence of post crania and lack of formal excavation meant that diagnosis and dating was uncertain. The aim of this research was to confirm the diagnosis using biomolecular means and second, to place it in context with other British leprosy cases using SNP genotyping and radiocarbon dating. METHODOLOGY: Bone from the skull was analysed by ancient DNA (aDNA) methods and subjected to radiocarbon dating. As a result, stable carbon and nitrogen isotope values were produced, both useful for assessing aspects of the woman’s diet.Results/Key findings. aDNA confirmed the presence of mycobacterium leprae and genotyping demonstrated an ancestral variant of subtype 3I, the same lineage recently identified in living squirrels in the south of England. Radiocarbon dating revealed the woman lived approximately between 885-1015 AD, providing evidence for endurance of this subtype in East Anglia, having been previously identified as early as the fifth-sixth century (Great Chesterford) and as late as the thirteenth century (Ipswich). CONCLUSIONS: The confirmation of a new pre-Norman leprosy case in East Anglia is of interest as this is where a high proportion of cases are located. Possible factors for this may include preservation and excavation biases, population density, but also connection and trade, possibly of fur, with the continent. Future research on other British LL cases should focus on exploring these aspects to advance understanding of the disease’s history, here and on the continent.

  • Jokimäki, J., Selonen, V., Lehikoinen, A. & Kaisanlahti-Jokimäki, M.-L. (2017) The role of urban habitats in the abundance of red squirrels (Sciurus vulgaris, L.) in Finland. Urban Forestry & Urban Greening 27: 100-108.

Abstract: Because the amount of urban areas has increased, it is important to investigate the abundance of wildlife species in relation to urban environments. Analyzing the impact of urbanization on the presence of forest-dwelling mammals is of interest due to the possible effects of urbanization on human-wildlife relationships and urban biodiversity. The Eurasian red squirrel (Sciurus vulgaris) is a declining forest species, and its occurrence in urban environments has been inadequately studied. The loss and fragmentation of forests due to urbanization may be detrimental for squirrels, whereas the abundant and predictable food resources and the low number of natural predators in urban areas may encourage squirrels to invade towns. We used large-scale data collected by volunteer bird watchers along a 950km south-north gradient to study whether the winter abundance of squirrels in Finland is dependent on urbanization, while controlling for effects of habitat type, food abundance (spruce cone crop; number of winter feeding sites), predator abundance (northern goshawk, Accipiter gentilis; feral cat Felis catus), season and latitude. We found that squirrel abundance increased with human population density, number of feeding sites and spruce cone crop and decreased with latitude and season. Feral cats showed weak negative connection with squirrel numbers, but there were no effect of goshawks. Relative squirrel abundance was approximately twice as high in urban habitats than in forests. Artificial feeding rather than a low number of predators may attract squirrels in urban environments. Planting spruce trees in urban environments will also benefit squirrels. Our results indicate that urban areas are an important habitat for the red squirrel even along the northern edge of their distribution range, where natural forest areas are still widespread. We conclude also that a citizen science −based bird survey protocol associated with mammal surveys seems to be a good large-scale monitoring method to study the urbanization of squirrels.

  • Jones, H., White, A., Lurz, P., & Shuttleworth, C. (2017) Mathematical models for invasive species management: Grey squirrel control on Anglesey. Ecological Modelling 359: 276-284.

Abstract: The control of invasive species and protection of threatened native species require well-developed policy and species management strategies. Mathematical models provide a key tool that can be used to test, develop and optimise strategies to manage invasive species. We use the native red squirrel and invasive grey squirrel system on the Island of Anglesey, UK, as a case study system in which to parameterise a mathematical model that includes the control of grey squirrels. We develop a stochastic, spatial model that represents the real habitat structure, distribution and linkage on Anglesey and the neighbouring mainland and includes the key population and epidemiological dynamics of the red-grey-squirrelpox system. The model also includes a representation of the trapping and removal of grey squirrels which is parameterised from field data on Anglesey in which grey squirrel were removed and red squirrels reintroduced between 1998–2013. The model is used to assess different management procedures to protect red squirrels from island re-invasion by grey squirrels, including the threat of squirrelpox spread posed by endemic mainland grey populations. The findings have important implications for the conservation of threatened red squirrels throughout the UK and in Europe. Moreover, the modelling framework is based on well-understood, classical models of competitive and epidemiological interactions and therefore the techniques can be adapted and applied more generally to manage the threat of invasive species in a wide range of natural systems.

  • Koprowski, J., Nieto-Montes de Oca, A., Palmer, G., Ramos-Lara, N. & Timm, R. (2017) Sciurus aureogaster (Rodentia: Sciuridae). Mammalian Species, 49, 81.
  • Lichti, N. I., Steele, M. A., & Swihart, R. K. (2017) Seed fate and decision-making processes in scatter-hoarding rodents. Biological Reviews 92: 474-504. doi:10.1111/brv.12240.

Abstract: A mechanistic understanding of seed movement and survival is important both for the development of theoretical models of plant population dynamics, spatial spread, and community assembly, and for the conservation and management of plant communities under global change. While models of wind-borne seed dispersal have advanced rapidly over the past two decades, models for animal-mediated dispersal have failed to make similar progress due to their dependence on interspecific interactions and complex, context-dependent behaviours. In this review, we synthesize the literature on seed dispersal and consumption by scatter-hoarding, granivorous rodents and outline a strategy for development of a general mechanistic seed-fate model in these systems. Our review decomposes seed dispersal and survival into six distinct sub-processes (exposure, harvest, allocation, preparation, placement, and recovery), and identifies nine intermediate (latent) variables that link physical state variables (e.g. seed and animal traits, habitat structure) to decisions regarding seed allocation to hoarding or consumption, cache placement and management, and deployment of radicle-pruning or embryo excision behaviours. We also highlight specific areas where research on these intermediate relationships is needed to improve our mechanistic understanding of scatter-hoarder behaviour. Finally, we outline a strategy to combine detailed studies on individual functional relationships with seed-tracking experiments in an iterative, hierarchical Bayesian framework to construct, refine, and test mechanistic models for context-dependent, scatter-hoarder-mediated seed fate.

  • Marvel-Coen, J. (2017). Finding new homes: Multilevel selection on birth timing and growth in North American red squirrels. Evolution 71(7): 1917-1918. doi:10.1111/evo.13293

Abstract: Individuals often interact more closely with some members of the population (e.g., offspring, siblings, or group members) than they do with other individuals. This structuring of interactions can lead to multilevel natural selection, where traits expressed at the group-level influence fitness alongside individual-level traits. Such multilevel selection can alter evolutionary trajectories, yet is rarely quantified in the wild, especially for species that do not interact in clearly demarcated groups. We quantified multilevel natural selection on two traits, postnatal growth rate and birth date, in a population of North American red squirrels (Tamiasciurus hudsonicus). The strongest level of selection was typically within-acoustic social neighborhoods (within 130 m of the nest), where growing faster and being born earlier than nearby litters was key, while selection on growth rate was also apparent both within-litters and within-study areas. Higher population densities increased the strength of selection for earlier breeding, but did not influence selection on growth rates. Females experienced especially strong selection on growth rate at the within-litter level, possibly linked to the biased bequeathal of the maternal territory to daughters. Our results demonstrate the importance of considering multilevel and sex-specific selection in wild species, including those that are territorial and sexually monomorphic.

  • Mazzamuto, M. V., Morandini, M., Panzeri, M., Wauters, L. A., Preatoni, D. G., & Martinoli, A. (2017) Space invaders: effects of invasive alien Pallas’s squirrel on home range and body mass of native red squirrel. Biological Invasions  n/a-n/a doi:10.1007/s10530-017-1396-2.

Abstract: Alien species can affect native species through several ecological processes such as competition. Here we tested the hypothesis of interspecific competition for space and food resources between the native Eurasian red squirrel and the invasive Pallas’s squirrel introduced in Italy. We used an experimental study design comparing space and habitat use and body condition parameters of red squirrels between areas of co-occurrence with the Pallas’s squirrel and areas without it. There were no differences in mean home range size of red squirrels between red-only areas and red-Pallas. However, when Pallas’s squirrels were removed, the red squirrels increased their home ranges. Moreover, in the area of syntopy, red squirrels had a higher degree of intraspecific home range overlap than in the red-only area. We also found indirect evidence for competition for food with red squirrels having a poorer body condition when co-occurring with the alien species. We analyzed the body mass and size of red squirrels in the two areas and our results showed that red squirrels had a reduced body mass and size when in syntopy, confirming that the interspecific competition does not allow red squirrels to reach the optimum body condition that they would have if the competitor was not present. Moreover, tree-species niche overlap was very high and both species fed primarily on the same tree seeds. Differences in vegetation cover between areas are discussed. This is the first study that confirms the invasiveness of the Pallas’s squirrel also in terms of capability to compete with native species.

  • Merrick, M. J., & Koprowski, J. L. (2017) Circuit theory to estimate natal dispersal routes and functional landscape connectivity for an endangered small mammal. Landscape Ecology 32: 1163-1179. doi:10.1007/s10980-017-0521-z.

Abstract: Natal dispersal links population dynamics to landscape connectivity. Understanding how organisms perceive barriers to movement, or landscape resistance, during natal dispersal is important to conserve and manage populations threatened by fragmentation and habitat loss.

  • Millins, C., Gilbert, L., Medlock, J., Hansford, K., Thompson, D. B., & Biek, R. (2017) Effects of conservation management of landscapes and vertebrate communities on Lyme borreliosis risk in the United Kingdom. Philosophical Transactions of the Royal Society B: Biological Sciences 372. doi:10.1098/rstb.2016.0123.

Abstract: Landscape change and altered host abundance are major drivers of zoonotic pathogen emergence. Conservation and biodiversity management of landscapes and vertebrate communities can have secondary effects on vector-borne pathogen transmission that are important to assess. Here we review the potential implications of these activities on the risk of Lyme borreliosis in the United Kingdom. Conservation management activities include woodland expansion, management and restoration, deer management, urban greening and the release and culling of non-native species. Available evidence suggests that increasing woodland extent, implementing biodiversity policies that encourage ecotonal habitat and urban greening can increase the risk of Lyme borreliosis by increasing suitable habitat for hosts and the tick vectors. However, this can depend on whether deer population management is carried out as part of these conservation activities. Exclusion fencing or culling deer to low densities can decrease tick abundance and Lyme borreliosis risk. As management actions often constitute large-scale perturbation experiments, these hold great potential to understand underlying drivers of tick and pathogen dynamics. We recommend integrating monitoring of ticks and the risk of tick-borne pathogens with conservation management activities. This would help fill knowledge gaps and the production of best practice guidelines to reduce risks.

  • Oberosler, V., Groff, C., Iemma, A., Pedrini, P., & Rovero, F. (2017) The influence of human disturbance on occupancy and activity patterns of mammals in the Italian Alps from systematic camera trapping. Mammalian Biology – Zeitschrift für Säugetierkunde.

Abstract: As human activities increase in natural areas, so do threats to wildlife, potentially leading to immediate and long-term impacts on species’ distribution, activity, reproduction and survival. This is particularly relevant for large-bodied vertebrates that are especially sensitive to human presence and human-driven habitat changes. Assessing the impact of anthropogenic disturbance requires data on species distribution and activity patterns of target species in relation to human presence and infrastructures. Here, we used camera trap data to study the influence of anthropogenic disturbance on the community of medium-to-large mammals in a mountainous area in the eastern Italian Alps, with emphasis on the local population of brown bear (Ursus arctos). In 2015, we sampled a study area of 220 km2 with 60 camera trap locations adopting a systematic grid. Such design was inspired by the terrestrial vertebrate monitoring protocol developed by the TEAM Network, a pan-tropical biodiversity programme. Camera traps run for 30 days in each site and cumulated 1,978 camera trapping days, yielding 1,514 detection events of 12 species of mammals. For the 8 most recorded species, we used detection/non-detection data to model estimated occupancy and detection probability in relation to a suite of environmental and disturbance covariates. Our analysis revealed that human disturbance plays a significant role in influencing species-specific detection probability, while we found little evidence of significant relationship between occupancy and anthropogenic disturbance. For example, we found that brown bear’s detectability was negatively correlated with capture rate of humans at sampling sites, and positively correlated with distance from settlements. We also assessed species-specific daily activity patterns and found that, for all species, the overlap with human diel pattern decreases significantly at sites with higher human presence. We also discuss the potential of our approach for building cost-efficient and long-term monitoring of mammals.

  • Sadeghi, M., & Malekian, M. (2017) The Persian squirrel of Kurdistan Province, western Iran: what determines its geographic distribution? Mammalia 81: 309-314.

Abstract: Here, we used the maximum entropy (MAXENT) method to predict habitat distribution of the Persian squirrel in oak forests of Kurdistan Province, western Iran. We used 70 points with known occurrence of the species and 17 environmental variables (climatic variables represented annual trends in temperature and precipitation, seasonality and extreme or limiting environmental factors) to map the species distribution. The MAXENT model showed high performance. Using a 0.5 logistic probability threshold, the models suggested about 16,783.5 ha of the study area to have high suitability for the Persian squirrel. These areas were thus estimated as “good” habitats. Amongst the environmental variables, land cover had the greatest role in the Persian squirrel’s distribution. Precipitation and temperature were the two major climatic factors that affected the Persian squirrel’s distribution. Gap analysis showed that many parts of the species habitat have remained unprotected what can threaten the survival of the studied species in the region. These findings can be used to develop conservation management plans and boost the network of protected areas in the region.

  • Selonen, V. & Wistbacka, R.  (2017) Role of breeding and natal movements in lifetime dispersal of a forest-dwelling rodent. Ecology and Evolution 7: 2204-2213.

Abstract: The lifetime movements of an individual determine the gene flow and invasion potential of the species. However, sex dependence of dispersal and selective pressures driving dispersal have gained much more attention than dispersal at different life and age stages. Natal dispersal is more common than dispersal between breeding attempts, but breeding dispersal may be promoted by resource availability and competition. Here, we utilize mark–recapture data on the nest-box population of Siberian flying squirrels to analyze lifetime dispersal patterns. Natal dispersal means the distance between the natal nest and the nest used the following year, whereas breeding movements refer to the nest site changes between breeding attempts. The movement distances observed here were comparable to distances reported earlier from radio-telemetry studies. Breeding movements did not contribute to lifetime dispersal distance and were not related to variation in food abundance or habitat patch size. Breeding movements of males were negatively, albeit not strongly, related to male population size. In females, breeding movement activity was low and was not related to previous breeding success or to competition between females for territories. Natal philopatry was linked to apparent death of a mother; that is, we did not find evidence for mothers bequeathing territories for offspring, like observed in some other rodent species. Our results give an example of a species in which breeding movements are not driven by environmental variability or nest site quality. Different evolutionary forces often operate in natal and breeding movements, and our study supports the view that juveniles are responsible for redistributing individuals within and between populations. This emphasizes the importance of knowledge on natal dispersal, if we want to understand consequences of movement ecology of the species at the population level.

  • Shonfield, J., Gorrell, J. C., Coltman, D. W., Boutin, S., Humphries, M. M., Wilson, D. R., et al. (2017) Using playback of territorial calls to investigate mechanisms of kin discrimination in red squirrels. Behavioral Ecology 28: 382-390.

Abstract: Kin recognition can facilitate kin selection and may have played a role in the evolution of sociality. Red squirrels (Tamiasciurus hudsonicus) defend territories using vocalizations known as rattles. They use rattles to discriminate kin, though the mechanism underlying this ability is unknown. Our objective was to distinguish between the mechanisms of prior association, where animals learn the phenotypes of kin they associate with early in life, and phenotype matching/recognition alleles, where animals use a template to match phenotypes, thereby allowing them to recognize kin without an association early in life. We used audio playbacks to measure the responses of squirrels to rattles from familiar kin, unfamiliar kin, and non-kin. Initial analyses revealed that red squirrels did not discriminate between familiar and unfamiliar kin, but also did not discriminate between kin and non-kin, despite previous evidence indicating this capability. Post hoc analyses showed that a squirrel’s propensity to rattle in response to playback depended on an interaction between relatedness and how the playback stimuli had been recorded. Red squirrels discriminated between rattles from close kin (r = 0.5) and rattles from non-kin (r &lt; 0.125) when the rattles were recorded from provoked squirrels. Squirrels did not exhibit kin discrimination in response to unsolicited rattles. Once we accounted for how the stimuli had been recorded, we found no difference in the responses to familiar and unfamiliar kin. Our study suggests that kin discrimination by red squirrels may be context dependent.

  • Shuttleworth, C. (2017). Grey squirrels are bad for the British countryside – full stop. The Conservation (April 6 2017).
  • Siracusa, E., Boutin, S., Humphries, M. M., Gorrell, J. C., Coltman, D. W., Dantzer, B., . . . McAdam, A. G. (2017). Familiarity with neighbours affects intrusion risk in territorial red squirrels. Animal Behaviour 133 (Supplement C), 11-20.

Abstract: Interactions with conspecifics are an important aspect of an individual’s environment. Although it is well known that the presence of conspecifics can have important effects on behaviour, in general it is also now acknowledged that the composition of the social environment can vary, and that this variation may have profound effects on individual behaviour and fitness. Using a wild population of North American red squirrels, Tamiasciurus hudsonicus, we investigated the importance of the composition of the social environment in a territorial species by assessing whether the risk of intrusion faced by territory owners varied with the degree of relatedness and familiarity in their social neighbourhoods. To test this, we conducted temporary removals of territory owners and observed the time until intrusion and the identity of intruding individuals. We found that individuals in neighbourhoods with low average familiarity faced a higher risk of intrusion and that unfamiliar neighbours were more likely to intrude. Surprisingly, we found that related neighbours also posed a higher risk of intrusion. The results from our study suggest that familiarity with neighbours may be an ecologically and evolutionarily relevant measure of the social environment, even in a species considered to be ‘asocial’. Future studies should consider the potential importance of the social environment, which has heretofore been mostly overlooked, as a relevant selective pressure in asocial, territorial species.

  • Steen, R., & Barmoen, M. (2017) Diel activity of foraging Eurasian red squirrels ( Sciurus vulgaris ) in the winter revealed by camera traps. Hystrix, the Italian Journal of Mammalogy 28  . doi:10.4404/hystrix-28.1-11997.

Abstract: Different animals are adapted to a range of activity patterns, from diurnal to nocturnal. Under normal conditions, the 24-hour rhythm is entrained by changes in light intensity during twilight, i.e. the light and dark cycle. Many rodent species exhibit predator avoidance by adjusting their activity in relation to space or time, which is weighed against the need for food. Hence, an individual’s foraging activity consists of a compromise between foraging and predation risk, in addition to competition. Our study species, the Eurasian red squirrel, is diurnal and utilises dense forest habitats. In the present study, we used non-invasive camera traps to model diel activity during the winter months in 2014-2015 (December to February 24-hour day). We found that the Eurasian red squirrels exhibited a strictly diurnal feeding activity pattern and the shape of the modelled activity curve was unimodal and concentrated in the daylight hours, starting at sunrise and peaking in the morning.

  • Sullivan, T. P., Ransome, D. B., Sullivan, D. S., Lindgren, P. M. F., & Klenner, W. (2017) Tree squirrel abundance and demography in managed coniferous forests of British Columbia are within the range of natural fluctuations of old-growth stands. Canadian Journal of Forest Research 47: 565-582. doi:10.1139/cjfr-2016-0458.

Abstract: The American red squirrel (Tamiasciurus hudsonicus Exrleben) and northern flying squirrel (Glaucomys sabrinus Shaw) are important mammal species in coniferous forests that are widely distributed across temperate and boreal ecological zones. Although T. hudsonicus and G. sabrinus apparently prefer late-successional forests, their population dynamics show no clear pattern in young second-growth and old-growth conifer forests. We used a compilation of study results that had standardized methodology and sampling effort to compare tree squirrel responses across a range of forest conditions. We tested the hypotheses (H) that abundance, reproduction, recruitment, and survival would be higher in (H1) old-growth than second-growth stands, (H2) unthinned than thinned second-growth stands, and (H3) lightly than heavily thinned stands. Tree squirrel populations in old-growth stands were considered the “standard” treatment to which other treatments in second-growth stands (unthinned and variously thinned) were compared. Thinned stands were grouped into low, medium, and high densities of trees. Datasets from seven published studies included 2804 Tamiasciurus and 837 G. sabrinus individuals, 25 study years, and 158 trapping periods. Mean abundance of Tamiasciurus was similar among treatment stands, ranging from 0.62 to 1.29·ha−1. Mean numbers of G. sabrinus were highest in old-growth stands at 0.65·ha−1, followed by the low- and medium-density stands at 0.50·ha−1, the high-density stands at 0.25·ha−1, and finally the unthinned second-growth stands at a low of 0.12·ha−1. In terms of effect size, mean proportional change in abundance, relative to that within old-growth stands, of both squirrel species in the three thinned stands were within the range of natural fluctuations in old-growth stands. Populations of Tamiasciurus in the unthinned stands were not within the range of fluctuations in the old-growth stands. Mean number of successful pregnancies and total recruits were similar among stands for Tamiasciurus, with variability in female breeding and winter survival. Mean number of recruits of G. sabrinus was highest in old-growth stands with no other differences in demographic attributes among stands. The biological significance of these differences in demographic variables was small in terms of effect sizes. Tamiasciurus and G. sabrinus seem to persist in a relatively broad range of young managed forest habitats, as well as in old-growth stands.

  • Turkia, T., Selonen, V., Danilov, P., Kurhinen, J., Ovaskainen, O., Rintala, J., & Brommer, J. (2017). Red squirrels decline in abundance in the boreal forests of Finland and NW Russia. Ecography  n/a-n/a. doi:10.1111/ecog.03093

Abstract: Recent global warming and other anthropogenic changes have caused well-documented range shifts and population declines in many species over a large spatial extent. Most large-scale studies focus on birds, large mammals, and threatened species, whereas large-scale population trends of small to medium-sized mammals and species that are currently of least concern remain poorly studied. Large-scale studies are needed because on a smaller scale, important patterns may be masked by local variation and stochastic processes. Here, we utilized snow track census data from Finland and NW Russia to estimate population growth rates of the Eurasian red squirrel (Sciurus vulgaris L) for a period of 17 years in an area of over 1 000 000 km2. We also studied the effects of changes in summer and winter temperatures, winter precipitation, predator abundance, and canopy cover on estimated red squirrel population growth rates. Our results suggest that red squirrel populations have declined in most parts of the study area, the only remarkable exception being SW Russia. These results are in concordance with previous studies suggesting that species that are still common and of least concern may be declining. However,our findings are in contrast to the common pattern of northern populations of boreal species increasing due to global warming. The estimated population growth rates are in synchrony over vast areas, suggesting that the underlying reasons also operate on a large scale. We indeed find that the population growth rate was lower in regions where winters warmed faster during the study period, suggesting that changes in the environment (or biotic changes associated with it) are linked with the decline of red squirrels.

  • Turner, J. M., Reher, S., Warnecke, L. & Dausmann, K. H. (2017) Eurasian Red Squirrels Show Little Seasonal Variation in Metabolism in Food-Enriched Habitat. Physiological and Biochemical Zoology 90(6): 655-662.

Abstract: Energy expenditure and ambient temperature (Ta) are intrinsically linked through changes in an animal’s metabolic rate. While the nature of this relationship is stable, the breadth of change in thermoregulatory cost varies with body size and physiological acclimatization to season. To explore seasonal metabolic changes of small mammals, we studied a population of Eurasian red squirrels (Sciurus vulgaris) in a seminatural environment with a year-round supply of natural and supplemented food. In each season we measured the metabolic rate of wild-caught red squirrels, using open-flow respirometry, and hypothesized that individuals would make adjustments to contend with seasonal weather conditions. In comparison to summer animals, we predicted that winter squirrels would show (1) an increase in metabolic rate within the thermoneutral zone, (2) a decrease in the lower critical temperature of the thermoneutral zone, (3) a shallower slope of resting metabolic rate with decreasing Ta, and (4) lower thermal conductance. Surprisingly, we observed only minor changes in resting metabolic rate, and energetic modeling suggested that the scope of change was unlikely to be of ecological consequence. Hair area density was higher in winter than in summer, corresponding to a slightly elevated thermal conductance in summer, while body mass was reasonably constant year-round. We conclude that the scope of physiological seasonal adaptation is minimal when food is abundant and that squirrels instead rely on adjustments in activity to reduce exposure to low Ta. We suggest that this may explain the squirrel’s success in a wide range of habitats, including urban areas, which require a rapid and flexible response to environmental changes and may indicate the capacity of other small mammal species to cope with environmental disturbance.

  • Tye, C. A., McCleery, R. A., Fletcher, R. J., Greene, D. U., & Butryn, R. S. (2017) Evaluating citizen vs. professional data for modelling distributions of a rare squirrel. Journal of Applied Ecology 54: 628-637. doi:10.1111/1365-2664.12682.

Abstract: * To realize the potential of citizens to contribute to conservation efforts through the acquisition of data for broad-scale species distribution models, scientists need to understand and minimize the influences of commonly observed sample selection bias on model performance. Yet evaluating these data with independent, planned surveys is rare, even though such evaluation is necessary for understanding and applying data to conservation decisions. * We used the state-listed fox squirrel Sciurus niger in Florida, USA, to interpret the performance of models created with opportunistic observations from citizens and professionals by validating models with independent, planned surveys. * Data from both citizens and professionals showed sample selection bias with more observations within 50 m of a road. While these groups showed similar sample selection bias in reference to roads, there were clear differences in the spatial coverage of the groups, with citizens observing fox squirrels more frequently in developed areas. * Based on predictions at planned field surveys sites, models developed from citizens generally performed similarly to those developed with data collected by professionals. Accounting for potential sample selection bias in models, either through the use of covariates or via aggregating data into home range size grids, provided only slight increases in model performance. * Synthesis and applications. Despite sample selection biases, over a broad spatial scale opportunistic citizen data provided reliable predictions and estimates of habitat relationships needed to advance conservation efforts. Our results suggest that the use of professionals may not be needed in volunteer programmes used to determine the distribution of species of conservation interest across broad spatial scales.

  • Wauters, L. A., Amori, G., Aloise, G., Gippoliti, S., Agnelli, P., Galimberti, A., et al. (2017) New endemic mammal species for Europe: Sciurus meridionalis (Rodentia, Sciuridae). 2017, 28.  doi:10.4404/hystrix-28.1-12015.

Abstract: Combining genetic, morphological and geographical data, we re-evaluate Sciurus meridionalis, Lucifero 1907 as a tree squirrel species. The species, previously considered a subspecies of the Eurasian red squirrel, Sciurus vulgaris, is endemic to South Italy with a disjunct distribution with respect to S. vulgaris. The new species has a typical, monomorphic coat colour characterized by a white ventral fur and a very dark-brown to blackish fur on the back, sides and tail. Specimens of S. meridionalis have a larger hind foot length and weigh about 35% more than live-caught S. vulgaris from northern Italy. S. meridionalis is larger than S. vulgaris specimens from three other regions in Italy for mandible length, skull width and skull (condylobasal) length, and principal component scores indicate significant shape differences of specimens from the Calabria population ( S. meridionalis ) compared to all other specimens ( S. vulgaris ). These morphological differences are further supported by genetic evidence at three mitochondrial markers (D-loop, cytochrome b and the DNA barcoding region COI) using the widest molecular dataset ever assembled for Sciurus vulgaris and S. meridionalis . All the investigated markers revealed exclusive haplotypes for S. meridionalis well separated from those of S. vulgaris and previously published results based on nuclear markers further support our taxonomic hypothesis. We suggest Calabrian black squirrel as common name for this new taxon.

  • Wibbelt G, T. S., Dabrowski PW, Kershaw O, Nitsche A, Schrick L. (2017) Berlin squirrelpox virus, a new poxvirus in red squirrels, Berlin, Germany. Emerging Infectious Diseases 23. (2017)

Abstract: Near Berlin, Germany, several juvenile red squirrels (Sciurus vulgaris) were found with moist, crusty skin lesions. Histology, electron microscopy, and cell culture isolation revealed an orthopoxvirus-like infection. Subsequent PCR and genome analysis identified a new poxvirus (Berlin squirrelpox virus) that could not be assigned to any known poxvirus genera.

  • Zelditch, M. L., Ye, J., Mitchell, J. S., & Swiderski, D. L. (2017) Rare ecomorphological convergence on a complex adaptive landscape: Body size and diet mediate evolution of jaw shape in squirrels (Sciuridae). Evolution, n/a-n/a. doi:10.1111/evo.13168.

Abstract: Convergence is widely regarded as compelling evidence for adaptation, often being portrayed as evidence that phenotypic outcomes are predictable from ecology, overriding contingencies of history. However, repeated outcomes may be very rare unless adaptive landscapes are simple, structured by strong ecological and functional constraints. One such constraint may be a limitation on body size because performance often scales with size, allowing species to adapt to challenging functions by modifying only size. When size is constrained, species might adapt by changing shape; convergent shapes may therefore be common when size is limiting and functions are challenging. We examine the roles of size and diet as determinants of jaw shape in Sciuridae. As expected, size and diet have significant interdependent effects on jaw shape and ecomorphological convergence is rare, typically involving demanding diets and limiting sizes. More surprising is morphological without ecological convergence, which is equally common between and within dietary classes. Those cases, like rare ecomorphological convergence, may be consequences of evolving on an adaptive landscape shaped by many-to-many relationships between ecology and function, many-to-one relationships between form and performance, and one-to-many relationships between functionally versatile morphologies and ecology. On complex adaptive landscapes, ecological selection can yield different outcomes.




Shuttleworth, C., Lurz, P., & Gurnell, J. (2016) The Grey Squirrel: Ecology & Management of an Invasive Species in Europe, 532 pp. European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK.


  • Gurnell, J. (2016). Foreword. The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: viii-ix.
  •  Bertolino, S., Lurz, P., Shuttleworth, C., Martinoli, A., & Wauters, L ((2016). The management of grey squirrel populations in Europe: evolving best practice. The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 495-514.

Abstract: Grey squirrel management is conducted in Great Britain, Ireland and Italy for red squirrel conservation and timber protection. However, management plans differ hugely with respect to aims, geographical scales, methodologies and costs. A key universal element linked to squirrel control is population monitoring. However, in the United Kingdom (UK) it took a lot of time to convince volunteer squirrel groups to accurately record control effort and success in order to allow subsequent analysis of population trends. In Italy, after decades of inaction, during which time grey squirrels colonized five regions due to translocations within the country, new management actions finally started. With the aid of two European co-funded projects, eradication and control activities have been initiated in the Lombardy, Piedmont, Liguria and Umbria regions. The removal of the grey squirrel from the island of Anglesey was the first eradication project which led to the complete removal of the species from a defined European area, though the bridge connections with the mainland necessitate continued interventions. More  recently, an urban  population was eradicated in Italy through live-trapping and surgical sterilization with subsequent release of the animals into other isolated parks. These two projects are key steps toward a widespread management of this American squirrel species, with the aims to spatially contain or even eradicate grey squirrel populations over large areas. While  the present legal framework ensures the possibility to manage alien squirrels and the available techniques are effective, there is still a need to work on communication skills to increase the consensus for alien species control among citizens, especially at a local scale

  • Cowan, D., Mill, A., Everest, D., Gomm, M., Mcinnes, C., Rushton, S., Shirley, M.D.F., Start, C. & Shuttleworth, C.M.(2016). The potential role of ectoparasites in the epidemiology of squirrelpox virus: a possible novel means of intervention to reduce the impact of the disease? . The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 255-274.

Abstract: The grey squirrel (Sciurus carolinensis) is considered a reservoir host of squirrelpox virus (SQPV) which poses a substantial epizootic threat to the native red squirrel (Sciurus vulgaris) in the United Kingdom (UK). Here we evaluate the potential contribution of ectoparasite vectored transmission of SQPV to the epidemiology of the disease. This includes information on ectoparasite abundance on grey squirrels (ectoparasites were recovered from 73% of grey squirrels examined) and in nest boxes (two species of flea were recovered from both grey and red squirrel nest boxes), along with SQPV sero-prevalence (69% of grey squirrels were sero-positive). These data were used, together with information from the literature, to model SQPV scenarios with and without ectoparasite vectored transmission in grey only, red only and mixed squirrel populations. The model predicted that SQPV cannot be maintained, particularly in grey squirrel populations, without ectoparasite vectored transmission. This hypothesis is testable by experimental manipulation. Such an experiment would involve monitoring changes in disease status in grey squirrel populations following administration of an appropriate insecticide. Such an experiment offers the prospect of developing an innovative means of disease intervention that could potentially eliminate the disease from grey squirrel populations considered to pose particular risks to red squirrel strongholds.

  • Dale, T. & J. Chantrey (2016). A subtle endemic virus in grey squirrels; squirrelpox virus. The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 211-233.

Abstract: Alien invasive species are well documented in posing a threat to indigenous species. Disease is increasingly being recognized as a mechanism by which an invasive species can have a negative outcome on native fauna. Where an alien species e.g. grey squirrel (Sciurus carolinensis), acts as a reservoir to introduce a novel pathogen e.g. squirrelpox virus (SQPV) to a naive native species e.g. red squirrel (S. vulgaris), it is important to understand the infection dynamics in the reservoir host. Polymerase chain reaction (PCR) analysis was used to identify SQPV infection in grey squirrels from an opportunistically sampled population in the United Kingdom (UK). This showed the virus to be a localised cutaneous infection, with samples from the lip and forelimb identifying the most infected individuals. Only slight epidemiological trends are observed, supporting SQPV as an endemic infection in grey squirrels in the UK. With only tenuous infection patterns being identified, methods for reducing infection in grey squirrels may prove ineffective in controlling the disease in their red counterpart. The study identifies areas for further investigation, while highlighting the need for large sample sizes when investigating pathogens with only subtle trends.

  • Derbridge, J., H. Pepper & J.L. Koprowski (2016). Economic damage by invasive grey squirrels in Europe. The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Woodbridge, Suffolk UK.: 393-405.

Abstract: Invasive alien species (IAS) comprise a global threat to biodiversity and may also cause economic harm by damaging natural resources and property. Indirect costs associated with IAS control and protection of native species add further economic burdens. The eastern grey squirrel (Sciurus carolinensis) is a successful invader in Europe, and this chapter reviews the current knowledge on the types and scale of damage it has inflicted on the continent’s economies.

  • Duff, J. & A. Meredith (2016). Disease and mortality of the grey squirrel The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 153-171.

Abstract: This chapter provides a timely, if non-exhaustive, list of pathogens, parasites and causes of disease and death recorded and published in grey squirrels (Sciurus carolinensis) both in North America (NA) and in Europe (EU). The viruses, bacteria and parasites that have been recorded in grey squirrels are listed, largely from extracts of published reports. Those which cause disease or are considered to be significant for other reasons are described. Mortality as a direct result of control operations, to protect timber crops, property or regional red squirrel (Sciurus vulgaris) populations, are excluded from this review and can be found described in Chapters elsewhere.

  • Flaherty, M., E. Goldstein & C. Lawton (2016). Predicting grey squirrel spread in Ireland; spatial tools for 37 future management of an invasive species The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 37-54.

Abstract: The invasive grey squirrel (Sciurus carolinensis) has successfully spread to cover the eastern half of Ireland since its introduction to the Irish midlands in 1911, but it has so far failed to spread west of the River Shannon. The species has declined in parts of its former range but the south, southwest and northwest of the island remain vulnerable to grey squirrel invasion. Managers  and ecologists can use spatial tools to devise a strategic approach to invasive species  management to minimise costs and maximise success. We demonstrate how these tools can be employed to devise a management approach to control the continuing expansion of this non-native species. Suitable habitat beyond the current grey squirrel range has been identified using a species distribution model. Predicted grey squirrel dispersal routes were highlighted using least cost pathway analysis. A spatially explicit population model examined grey squirrel expansion in the south and southwest of the island, where the species continues to spread. Results from discriminant analysis suggested the failure of grey squirrels to expand into certain areas and the recent decline or disappearance in part of their former range were correlated with pine marten (Martes martes) presence and habitat fragmentation. Through these spatial analyses, we identified future monitoring locations and effective control strategies to inform a more strategic management approach to limit the spread of the grey squirrel in Ireland.

  • Gurnell, J., P. Lurz & C.M. Shuttleworth (2016). Ecosystem impacts of an alien invader in Europe, the grey squirrel Sciurus carolinensis. The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. W. W. Lurz and J. Gurnell, The Grey Squirrel: Ecology & Management of an Invasive Species in Europe: 307-326.

Abstract: Grey squirrels (Sciurus carolinensis) are native to the eastern part of North America and were first introduced to Great Britain in 1876 and into northern Italy in 1948. From their centres of introduction they have expanded their range resulting in two widely recorded impacts: they outcompete and replace the native red squirrel (S. vulgaris) and damage trees with economic and aesthetic consequences. However, there may be other less apparent or less studied impacts of the alien invader in its new environment, some which may disrupt ecosystems but others that may have positive ecological or socio-economic function, and some that may only become apparent over time. Although invasive grey squirrels fill a similar niche to the usurped red squirrels, they are larger, live at higher densities in broadleaf woodlands, preferentially exploit the seed crops of tree species differently and are more terrestrial. The forest and woodlands they have moved into also differ to their homeland, for example, in terms of tree species richness and diversity. These factors together with the uncertainties of, for example, the effects of climate change on habitats, make it difficult to predict the importance of some of the less studied impacts. These may become more apparent in time and particularly if grey squirrels continue to expand their range in Europe. In this article, we overview the range of ecosystem impacts of invasive grey squirrels in Europe and, based on our current knowledge, provide a classification of the impact mechanism, the outcome (whether positive or negative) and whether the impact is widespread or occurs locally within the new range of grey squirrels. In many cases, it is clear that we do not have enough information to assess the level of importance of a particular impact and we acknowledge that the classification is provisional and likely to change. Nevertheless, we hope it offers a framework to direct further study to fill in the gaps in our knowledge

  • Gurnell, J. & H. Pepper (2016). The control and management of grey squirrel populations in Britain. The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 407-436.

Abstract: Grey squirrels (Sciurus carolinensis) were first introduced from North America to Britain in 1876 and further introductions and translocations within the country were recorded until 1929. Grey squirrels spread from these early points of introduction and are now found throughout much of the country. As early as 1917, concerns were expressed about the possible impact of grey squirrels on native red squirrels (S. vulgaris), to be followed in the 1920s by interest in impacts of grey squirrels on forestry. By the 1930s, the concerns of many landowners had translated into how to manage or control grey squirrels on their land. At the time, the British Government was sympathetic but did not campaign to eradicate grey squirrels; a Grey Squirrel (Prohibition of Importation and Keeping) Order came in to effect in 1937. After the Second World War the control and management of grey squirrels took on greater importance, particularly with respect to tree damage prevention. Extensive control of grey squirrels for red squirrel conservation started later, in the 1990s. In this paper, we discuss the management of grey squirrels with particular reference to Britain since the Second World War. First, we consider management strategies, including the importance of monitoring and bounty schemes that took place in the 1950s. We then discuss different control techniques (shooting, cage trapping, kill trapping, habitat management) and their effectiveness using examples from the literature that provide data on control effort. Now that warfarin poison can no longer be used as a plant protection product, grey squirrel control for both tree damage prevention and red squirrel conservation will depend on trapping and shooting for the foreseeable future. Cage trapping is the preferred method for control at the landscape level, backed up where possible by opportunistic shooting or shooting at feeders. To this end, we provide information on cage trapping best practice and consider the costs and the sociological dimension to the management of grey squirrels, particularly now that large numbers of volunteers are involved in controlling grey squirrels for red squirrel conservation

  • Halliwell, E., C. Shuttleworth, S. Cartmel, I. Lloyd & R. Jenkins (2016). Experiences of grey squirrel management in an upland conifer forest. The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 453-472.

Abstract: The introduced grey squirrel (Sciurus carolinensis) has replaced the native red squirrel (Sciurus vulgaris) across large parts of its range in the British Isles. As this replacement took place, red squirrels appeared to have a competitive advantage in upland Sitka spruce dominated forests. Consequently in mainland Britain large areas of upland coniferous plantation were strategically designated as red squirrel strongholds in what has been described as a ‘conifer forest management strategy’. Clocaenog forest in north Wales was one such site where habitat management, in conjunction with grey squirrel control, was used as the approach to safeguard the nationally important red squirrel population. In this paper we review twenty years of data gathered during research and control operations to examine the pattern of grey squirrel incursion and population establishment in this upland spruce plantation. Our findings suggest that grey squirrels may be able to utilise such habitats to a greater extent than previously considered and we examine the implications for red squirrel conservation strategies

  • Hayssen, V. (2016). Reproduction in grey squirrels: from anatomy to conservation The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 115-180.

Abstract: Grey squirrels (Sciurus carolinensis) are familiar denizens of many temperate woodlands. When introduced to new areas their reproductive productivity threatens native species, such as the Eurasian red squirrel (Sciurus vulgaris). Thus their reproductive biology is important to conservation efforts. Anatomy and physiology are two components of reproductive biology. Knowledge of reproductive anatomy lets scientists identify reproductive condition while understanding the reproductive cycle helps managers know when to time efforts for population control. This chapter reviews what is currently known about the reproductive biology of grey squirrels from their anatomy and physiology to the timing of their reproductive patterns. It ends with a brief review of current efforts to use contraception to control squirrel numbers.

  • Jones, H., A. White, P.W.W. Lurz, M. Boots, & C.M. Shuttleworth (2016). Mathematical models of grey squirrel invasion: a case study on Anglesey. The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 235-252.

Abstract: A spatial, stochastic model to represent the dynamics of red squirrels (Sciurus vulgaris) and grey squirrels (Sciurus carolinensis) and squirrelpox infection is developed to understand the documented replacement of red squirrels by grey squirrels which occurred on the Isle of Anglesey between approximately 1966 and 1998. The model results compare well with the observed historical field data and indicate that competition was the key process responsible for red squirrel decline. Squirrelpox virus (SQPV), which was prevalent in grey squirrels both on the mainland and latterly as they colonized Anglesey, failed to spread extensively through the resident red squirrel populations on the island. Model findings showed that disease outbreaks may occur in relatively high density red squirrel populations at the local level where reds were sympatric to greys, but at the larger scale, red squirrel densities were too low and/or too fragmented to maintain continual intra-specific spread of pathological infection. This finding has important consequences for applied conservation management and suggests that pathological squirrelpox outbreaks may be localised and the risk of extensive squirrelpox spread through low density red squirrel populations may be low

  • Koprowski, J., K. Munroe & A. Edelman (2016). Gray not Grey: Ecology of Sciurus carolinensis in native range in North America The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 1-17.

Abstract: Eastern grey squirrels (Sciurus carolinensis) have been introduced to numerous locations around the globe and are considered to be one of the world’s worst invasive species. The species has become notorious for its role as a biological invasive and a pest outside of its natural distribution. The basic ecology of the species does not appear to differ dramatically between native and naturalized lands. However, in deciduous and mixed forests of eastern North America to which they are native, eastern grey squirrels are a welcome species that are rarely  considered problematic. Herein, we examine the ecology of eastern grey squirrels in their native habitats where problems of overpopulation, damage or ecological dominance are rarely encountered.

  • Lawton, C., C. Shuttleworth &n R.E. Kenward (2016). Ranging Behaviour, Density And Social Structure In Grey Squirrels The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 133-150.

Abstract: The home range is a settled area in which an animal conducts its daily activities such as feeding, resting and breeding. Within the home range, the animal will have core areas; small  regions where it spends a disproportionate amount of time. There is considerable variation in grey squirrel home range size, as ranging behaviour is influenced by a number of factors. These may be environmental in nature (e.g. habitat type, food availability, degree of fragmentation), or related to population demographics and social interactions. Seasonal variation in home range use is also evident, and can be related to changes in food availability, or intra-specific interactions during breeding or dispersal. Grey squirrels (Sciurus carolinensis) display a hierarchical social  system, with males usually dominant over females, and adults over subadults. Females will  defend exclusive core areas from unrelated females, but overlap in home range core area is tolerated by males. Information on ranging behaviour gained through telemetry studies has proved to be essential in evolving grey squirrel management. It has helped to optimise control programmes and resource use.Everest, D., Floyd, T., Donnachie, B., Irvine, R., Holmes, J., & Shuttleworth, C. (2017). Confirmation of squirrelpox in Welsh red squirrels. Veterinary Record, 181, 514-515.

  • Leaver, L. A., Jayne, K., & Lea, S. E. G. (2016) Behavioral flexibility versus rules of thumb: how do grey squirrels deal with conflicting risks? Behavioral Ecology 28: 186-192.

Abstract: In order to test how flexibly animals are able to behave when making trade-offs that involve assessing constantly changing risks, we examined whether wild Eastern grey squirrels showed flexibility of behavioral responses in the face of variation in 2 conflicting risks, cache pilferage, and predation. We established that cache pilferage risk decreased with distance from cover and was thus negatively correlated with long-term predation risk. We then measured changes in foraging and food-caching behavior in the face of changes in the risk of predation and food theft over a short time-scale. We found that, overall, squirrels move further away from the safety of cover when they cache, compared to when they forage, as predicted by pilferage risk. However, there was no effect of immediate pilferage or predation risk (i.e., the presence of potential predators or pilferers) on the distance from cover at which they cached, and only a slight increase in forage distance when predation risk increased. These results suggest that “rules of thumb” based on static cues may be more cost-effective for assessing risk than closely tracking changes over time in the way suggested by a number of models of risk assessment.

  • Macpherson, J., H. Denman, D. Tosh, C. McNicol & E.C. Halliwell (2016). A review of the current evidence for impacts of the pine marten (Martes martes) on non-native and native squirrel populations. The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 289-304.

Abstract: The interaction between the European pine marten (Martes martes) and the American eastern grey squirrel (Sciurus carolinensis) has recently become the subject of much public and media interest in the United Kingdom (UK) and Ireland. The range of the grey squirrel has only coincided with the range of the European pine marten in recent years in both Ireland and Scotland. In both countries, native pine marten populations have begun to recover following historical persecution and grey squirrels are an introduced, invasive species. Distributional evidence from a study in Ireland has provided a first attempt to substantiate the potential suppressant effect pine martens could have on grey squirrel populations, with a subsequent positive impact on the native red squirrel (Sciurus vulgaris). Studies in the UK and from elsewhere show that the interactions between martens and squirrels are clearly complex and influenced by a number of different factors. These are reviewed and the implications for both red and grey squirrels discussed, along with the need for further research

  • Merrick, M., K. Evans & S. Bertolino (2016). Urban grey squirrel ecology, associated impacts, and management challenges The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 57-77.

Abstract: Grey squirrels (Sciurus carolinensis) are common inhabitants of wooded urban and suburban parks throughout their native and introduced range. The ecology of grey squirrels in rural environments has been the focus of considerable research, yet the ecology, behaviours, economic impact, and conservation implications of urban grey squirrels continue to gain increasing attention. In this chapter, we summarise key ecological characteristics of grey squirrels within an urban/suburban environment and how these differ from those observed in rural environments, the ecological role grey squirrels play in an urban ecosystem, and associated management challenges. Whilst urban and rural grey squirrels select similar habitats, urban  populations can occur at much higher densities than their rural counterparts, from which they  exhibit behavioural differences. Urban grey squirrels provide a wide range of ecosystem services, including cultural services that result in many urban dwellers having positive attitudes towards grey squirrels. This presents challenges for managing conflicts that can arise due to the damage that grey squirrels can cause to infrastructure, vegetation and other wildlife. Understanding basic  ecology and population dynamics of urban grey squirrels, particularly in their introduced range, is essential for predicting their risk of invasion and spread, impacts on native wildlife, and for designing control programmes.

  • Merrick, M. J., & Koprowski, J. L. (2016) Altered natal dispersal at the range periphery: The role of behavior, resources, and maternal condition. Ecology and Evolution n/a-n/a. doi:10.1002/ece3.2612.

Abstract: Natal dispersal outcomes are an interplay between environmental conditions and individual phenotypes. Peripheral, isolated populations may experience altered environmental conditions and natal dispersal patterns that differ from populations in contiguous landscapes. We document nonphilopatric, sex-biased natal dispersal in an endangered small mammal, the Mt. Graham red squirrel (Tamiasciurus hudsonicus grahamensis), restricted to a single mountain. Other North American red squirrel populations are shown to have sex-unbiased, philopatric natal dispersal. We ask what environmental and intrinsic factors may be driving this atypical natal dispersal pattern. We test for the influence of proximate factors and ultimate drivers of natal dispersal: habitat fragmentation, local population density, individual behavior traits, inbreeding avoidance, competition for mates, and competition for resources, allowing us to better understand altered natal dispersal patterns at the periphery of a species’ range. A juvenile squirrel’s body condition and its mother’s mass in spring (a reflection of her intrinsic quality and territory quality) contribute to individual behavioral tendencies for movement and exploration. Resources, behavior, and body condition have the strongest influence on natal dispersal distance, but affect males and females differently. Male natal dispersal distance is positively influenced by its mother’s spring body mass and individual tendency for movement; female natal dispersal distance is negatively influenced by its mother’s spring body mass and positively influenced by individual tendency for movement. An apparent feedback between environmental variables and subsequent juvenile behavioral state contributes to an altered natal dispersal pattern in a peripheral population, highlighting the importance of studying ecological processes at the both range center and periphery of species’ distributions.

  • Millens, C., D. Everest & A. Brereton (2016). The role of invasive grey squirrels as hosts of selected viruses, bacteria and parasites; implications for conservation and public health. The Grey Squirrel: Ecology & Management of an Invasive Species in Europ. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 173-190.

Abstract: The introduction of invasive vertebrate hosts can result in changed parasite dynamics, with implications for native species conservation and human health. While the association of invasive grey squirrels (Sciurus carolinensis) and squirrelpox virus (SQPV) with red squirrel (S. vulgaris) decline in the United Kingdom (UK) is well documented, the effect of grey squirrel introduction on the dynamics of other infections and parasites has been less intensively studied. Here, we review current knowledge of invasive grey squirrels as hosts of selected viruses (adenovirus and rotavirus), bacteria (Borrelia burgdorferi sensu lato and Bartonella) and protozoa (Hepatozoon) to assess potential impacts on red squirrels and public health. We describe the known distribution of these organisms in grey and red squirrels in Europe, pathogenicity and methods of detection. We found that knowledge of each pathogen’s distribution and assessment of the risk of cross-species transmission are limited by the opportunistic nature of sampling and limited molecular strain typing. For all organisms, sampling from sympatric grey and red squirrel populations and applying molecular strain typing will improve knowledge for potential crossspecies transmission and reservoir host associations. In the context of theselected viruses, bacteria and protozoa considered in this chapter (SQPV is considered separately in this book), adenovirus is associated with the most significant pathogenic effects and mortality in red squirrels and should therefore be a priority for further research

  • Nichols, C. & R. Gill (2016). Bark stripping behaviour by the grey squirrel, Sciurus carolinensis. The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 369-390.

Abstract:Grey squirrels (Sciurus carolinensis) damage trees by stripping bark and ingesting the underlying phloem. Damage has negative impacts on forest regeneration, and reduces timber value, imposing an economic toll on forestry in the United Kingdom (UK). A literature review was conducted to explore bark stripping behaviour. Papers were categorized according to their focus to analyse shifting research attitudes. Factors affecting damage likelihood are well known. Tree physiology, e.g. phloem width, age, species and habitat characteristics can affect the probability of damage, and the main bark stripping season is April to July. The motivations for grey squirrels to strip bark are still unclear. Putative motivators for damage include a fondness for sugar, phloem as a food source, agonistic encounters, and calcium deficiency. Over time, the bark stripping literature has shifted focus from research into predictive factors and causes, to monitoring impacts and improving squirrel control. Returning research focus to underlying causes of bark stripping may aid the production of humane, low-cost, low-effort preventive methods. Current and future research will focus on exploring the calcium hypothesis and investigating the effects of the pine marten (Martes martes) on grey squirrels. The potential impact of grey squirrels in Europe makes research into preventative measures urgent

  • Romeo, C., L. Wauters & N. Ferrari (2016). Parasites of grey squirrels: an additional threat to red squirrels in Italy? The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. W. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 193-209.

Abstract: Parasitic infections in north Italian populations of alien grey squirrels (Sciurus carolinensis) and native red squirrels (S. vulgaris) were investigated to (i) verify whether the invader lost, introduced or acquired any parasite species following its introduction into the new range and (ii) detect any alteration to native hosts’ parasite community induced by grey squirrels. Overall, results of field studies show that introduced grey squirrels harbour an impoverished parasite community compared to their native range and this reduction in parasite pressure may have facilitated their establishment and spread, as postulated by the enemy-release hypothesis. However, the invader introduced to Italy the North American nematode Strongyloides robustus which successfully spilled over to potentially naive red squirrels, as revealed by subsequent analysis of native hosts co-inhabiting with the alien congener. In addition, where grey squirrels are present, a significant increase in prevalence of infection by a local parasite Trypanoxyuris sciuri has been observed, suggesting that competition with invaders may indirectly reduce red squirrels’ ability to cope with parasitic infections. These findings highlight the need to further investigate the role of parasites in the red-grey squirrel system, both in the context of enemy-release facilitating invasion and as an added threat to red squirrel conservation

  • Scheibe, J. & N. Moncrief (2016). Morphometric divergence and functional similarity in Sciurus vulgaris and Sciurus carolinensis The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 79-95.

Abstract: We used geometric morphometric techniques to explore and compare th shapes of dentaries and skulls in four species of tree squirrels: Eurasian red squirre (Sciurus vulgaris), eastern grey  squirrel (S. carolinensis), eastern fox squirre (S. niger) and western grey squirrel (S.  griseus). These species were chose because of current competitive interactions amongst the species, and becaus of their  phylogenetic affinities. A canonical variates analysis of  Procruste shape coordinates revealed significant shape differences between the skull and  dentaries of S. carolinensis and S. vulgaris. We compared biomechanica properties of the dentaries for the four species, and used discriminant functio analysis to discriminate between the species in a jaw-function space. Here there was extensive functional overlap between S. carolinensis and S. vulgaris but not between S. carolinensis and S. niger. Although the skulls and dentarie of S. carolinensis and S. vulgaris differ morphologically, they are functionall similar.

  • Shuttleworth, C., E. Halliwell & P.A. Robertson (2016). Identifying incursion pathways, early detection responses and management actions to prevent grey squirrel range expansion: an island case study in Wales. The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 475-492.

Abstract: Grey squirrels (Sciurus carolinensis) are a non-indigenous species in the United Kingdom (UK) and were eradicated from the island of Anglesey in 2013 through a live-trapping based control programme. In parallel with the eradication effort, native red squirrel (Sciurus vulgaris) population restoration occurred. Red squirrels are a charismatic species, popular with the general public, and consequently people frequently provide supplemental foods for animals on garden bird tables or within squirrel feeding hoppers. The existence of these feeding stations, along with online social media platforms encouraging the reporting of squirrel sightings, resulted in the progressive evolution of a ‘community based’ network for monitoring squirrels. It was anticipated that this level of surveillance would lead to the early detection of grey squirrel incursion onto the island. Incursion contingency plans were drafted in 2008 and annual proactive surveillance trapping was established within woodland near the railway bridge linking Anglesey with the mainland. Against this background, a series of grey squirrel sightings were reported by the public during the autumn of 2015. This information led to the capture of three individuals. However, reporting by the public also included the misidentification of red squirrels as grey squirrels (false positives), unnecessarily increasing trapping efforts and highlighting a confounding factor in landscapes with sympatric squirrel populations. In this Chapter, we critically review the efficiency of reporting mechanisms, responses to sightings and factors affecting interventions. Decisions with regards to the partitioning of resources in response to grey squirrel sightings were influenced by several factors. A targeted response had to balance an array of available sighting evidence, information that often related to geographically discrete areas which,  on Anglesey, precluded simultaneous action within separate locations. This ultimately meant that managers had to implement a sequential prioritisation of removal measures

  • Shuttleworth, C., V. Selonen & J.L. Koprowski (2016). Grey squirrel nesting ecology and the use of nest sites in European population management. The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 349-367.

Abstract: Grey squirrels (Sciurus carolinensis) are an arboreal species that construct leaf nests (dreys) high in the woodland canopy. They will also den within tree cavities and inside artificial den sites such as wooden boxes. Occasionally, individuals will build a nest within the eaves or attic roof spaces of buildings. In this paper, we review the nesting behaviour of grey squirrels, examine nest site occupancy as a means of monitoring population abundance, review the control of grey squirrels whilst using different nest sites, and consider how an understanding of nesting behaviour might help evolve grey squirrel control programmes in Europe. Although there are several detailed studies of nest box use in North American populations, across Europe there remain only limited data with respect to artificial dens. We report nest box use by grey squirrels in Britain before highlighting opportunities for future ecological study, which may assist in managing this invasive pest species. In this context, we make reference to findings of long-term nest box studies of European red squirrel (S. vulgaris) and flying squirrels that require replication.

  • Signorile, A. & C. M. Shuttleworth (2016). Genetic evidence of the effectiveness of grey squirrel control operations: lessons from the Isle of Anglesey. The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 439-451.

Abstract: Eradication and control of Invasive Alien Species (IAS) populations presents a major challenge to the preservation of natural environments. Issues relating to the costs, logistics and social acceptance of eradications can undermine the success of management interventions and lead to failures. In this study, we examine grey squirrel genetics over a seven year period during which an island population was subjected to an eradication programme. The aim was to assess temporal changes in genetic diversity, population structure and inbreeding levels and also, to detect gene flow from the mainland. Our data show that the reduction in the number of individuals present on the island led to a marked genetic disequilibrium, reduced genetic diversity, high levels of inbreeding and clustering of individuals in fragmented populations. A very moderate gene flow was detected from the mainland to the island. These results indicate that intensive and continuous culling operations can disrupt the genetic patterns of a thriving invasive population and accelerate eradication even in non-isolated populations. The results also suggest that population genetics can be applied as an effective tool in investigating the ongoing success of an eradication process

  • Steele, M. & L.A. Wauters (2016). Diet and food hoarding in eastern grey squirrels (Sciurus carolinensis): implications for an invasive advantage The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 97-113.

Abstract: The invasive advantage of the eastern grey squirrel (Sciurus carolinensis) in its introduced range of Europe likely follows from its broad, opportunistic diet, and its ability to scatter-hoard seeds of many hardwood species such as oaks (Quercus spp.) and to manage these resources through periods of food scarcity, even in the face of intense competition with other rodents. We review the dietary patterns reported for this species, the seasonal and geographic variation in the diet, and the limited information on diet breadth of grey squirrels in Europe. We also describe the behaviour of scatter-hoarding by grey squirrels, and how seed characteristics such as seed perishability (due to germination schedules or insect infestation), seed size and seed chemistry influence scatter-hoarding decisions. We discuss the close evolutionary relationship between grey squirrels and the oaks, as evidenced by the innate basis of embryo removal, which significantly extends storage time. We also highlight recent studies that demonstrate that grey squirrels can maintain a hoarder’s advantage—in part, by deceiving potential pilferers about cache locations—but also by storing seeds in open habitats where pilferage is reduced. We conclude that many of the adaptive strategies this species exhibits for storing seeds may provide it with a competitive advantage in an introduced setting

  • Sullivan, S., A. Sullivan & J. S. Brown (2016). Citizen Scientists: fundamental partners in squirrel monitoring. The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 329-346.

Abstract: Monitoring squirrel populations across broad areas can be challenging especially in the patchwork of anthropogenic environments that range from urban neighbourhoods to rural tree plantations. The rapid and unpredictable change of such habitats, along with legal, logistical, and physical barriers to workers can hinder traditional data collection. Project Squirrel was designed as a way to overcome these barriers while also making connections between non-scientists and their local ecology. Fluid and rapidly changing populations in human-dominated habitats are best tracked by citizen scientists. These enthusiastic volunteers can provide accurate and timely observations from a greater number of locations than could ever be visited by professional scientists or covered by autonomous data collection devices. Repeated observations from the same location provide a timely, low-cost understanding of species occurrence and change in distribution. Sciurids are particularly amenable to observation by the general public because they are primarily diurnal, charismatic and are readily identified. Citizen scientists are self-selecting individuals and generally well aware of their own degree of environmental knowledge (70% vs 56% for reference group). However, they are a diverse group, so data collection methodologies must accommodate non-specialist abilities. Formative evaluation and periodic review of data collection tools can facilitate their accurate use by participants. Focused training to develop skill sets beyond the common knowledge of the general public may be necessary. Similarly, evaluation of participant skills allows confidence in the accuracy of submitted data. Intense and repeated participant recruitment is necessary to ensure an adequate number of data submissions over time. Through careful study design and standardized data collection practices, citizen scientists can be powerful partners to effectively monitor the ecological change occurring in their neighborhoods that, in turn, may impact a region or even a country.

  • Shuttleworth, C., P. Lurz & J. Gurnell (2016). Grey squirrel management in Europe – the future. The Grey Squirrel: Ecology & Management of an Invasive Species in Europe. C. Shuttleworth, P. Lurz and J. Gurnell, European Squirrel Initiative, Stoneleigh Park, Warwickshire CV8 2LG UK: 517-519.


Journal references

  • Avanzi C, del-Pozo J, Benjak A, Stevenson K, Simpson VR, Busso P, et al. (2016) Red squirrels in the British Isles are infected with leprosy bacilli. Science. 354(6313): 744-7.

Summary: With the exception of armadillos in the Americas, leprosy infections are considered almost exclusively restricted to humans. Avanzi et al. examined warty growths on the faces and extremities of red squirrels in the British Isles and found that two species of leprosy-causing organisms were to blame. Mycobacterium leprae in the southern population of Brownsea Island squirrels originated from a medieval human strain. M. lepromatosis was found in red squirrels from elsewhere in the United Kingdom and Ireland. Human leprosy is proving hard to eradicate, despite available drugs. Perhaps other wildlife species are also reservoirs for this stubborn disease. Leprosy, caused by infection with Mycobacterium leprae or the recently discovered Mycobacterium lepromatosis, was once endemic in humans in the British Isles. Red squirrels in Great Britain (Sciurus vulgaris) have increasingly been observed with leprosy-like lesions on the head and limbs. Using genomics, histopathology, and serology, we found M. lepromatosis in squirrels from England, Ireland, and Scotland, and M. leprae in squirrels from Brownsea Island, England. Infection was detected in overtly diseased and seemingly healthy animals. Phylogenetic comparisons of British and Irish M. lepromatosis with two Mexican strains from humans show that they diverged from a common ancestor around 27,000 years ago, whereas the M. leprae strain is closest to one that circulated in Medieval England. Red squirrels are thus a reservoir for leprosy in the British Isles.

Biancardi, C., & Gnoli, C. (2016) A review of Sciurus Group studies on the red squirrel (Sciurus vulgaris): presence, population density and colour phases in Lombardy (Italy). Natural History Sciences. Atti Soc. it. Sci. nat. Museo civ. Stor. nat. Milano 3: 27-34.

Abstract: During the nineties of the last Century, under the inspiration  of  Luigi  Cagnolaro,  it  had  been  founded  a  “Sciurus  group”, within the Research Centres of the Società Italiana di Scienze Naturali. Aim of the group was to start a campaign of researches on red squirrel populations in Lombardy, Italy promoting field master thesis on various topics: colour  phases and  indirect estimations of population densities. The researches  were carried out  during 10 years  in 5 study  areas. An investigation and census  with questionnaires  were started in  parallel, with  the  collaboration  of  Forest  Guards  (CFS),  Ecological  Guards (GEV) and students of biological and natural sciences. The results were published in Italian or exposed in national and international congresses. This review has the purpose  to show and  critically discuss the overall results, and make them available to a broader audience. The dark colour phase, in  the red  squirrel, resulted  associated to  elevation and  conifer woodlands, according  to the thermoregulation theory, which  consider the dark  fur thicker and more  suitable in  cold environments. Squirrel population  densities  are  subject  to  periodical  fluctuations,  in  conifer woodlands, due  to cones availability. Cone  crops are  subject to cycle with years of great production followed by years of lean. The recorded squirrel densities are  middle-lows, but  in line with  data from  similar environments

  • Bisi, F., von Hardenberg, J., Bertolino, S., Wauters, L. A., Imperio, S., Preatoni, D. G., et al. (2016) Current and future conifer seed production in the Alps: testing weather factors as cues behind masting. European Journal of Forest Research, 1-12. doi:10.1007/s10342-016-0969-4.

Abstract: Temporal patterns of masting in conifer species are intriguing phenomena that have cascading effects on different trophic levels in ecosystems. Many studies suggest that meteorological cues (changes in temperature and precipitation) affect variation in seed-crop size over years. We monitored cone crops of six conifer species in the Italian Alps (1999–2013) and analysed which seasonal weather factors affected annual variation in cone production at forest community level. Larch, Norway spruce and silver fir showed masting while temporal patterns in Pinus sp. were less pronounced. We found limited support for the temperature difference model proposed by Kelly et al. Both seasonal (mainly spring and summer) temperatures and precipitations of 1 and 2 years prior to seed maturation affected cone-crop size, with no significant effect of previous year’s cone crop. Next, we estimated future forest cone production until 2100, applying climate projection (using RCP 8.5 scenario) to the weather model that best predicted variation in measured cone crops. We found no evidence of long-term changes in average cone production over the twenty-first century, despite increase in average temperature and decrease in precipitation. The amplitude of predicted annual fluctuations in cone production varies over time, depending on study area. The opposite signs of temperature effects 1 and 2 years prior to seed set show that temperature differences are indeed a relevant cue. Hence, predicted patterns of masting followed by 1 or more years of poor-medium cone production suggest a high degree of resilience of alpine conifer forests under global warming scenario.

  • Brady Matthew, J., Koprowski John, L., Gwinn, R. N., Jo, Y.-S., & Young, K. (2016) Eastern fox squirrel (Sciurus niger, Linnaeus 1758) introduction to the Sonoran Desert Mammalia.

Abstract: The eastern fox squirrel, native to the eastern and midwestern United States, was recently documented in the Sonoran Desert in the vicinity of Yuma, Arizona, constituting the first state record for this species. We surveyed the people of Yuma to determine when and how the squirrels arrived. The squirrels were first observed in the 1960s, but may have been resident for a longer period. Since the 1960s, squirrels have spread throughout the city limits and extended south ~15 km into Somerton, Arizona. How the squirrels arrived is not clear, but must be the result of an introduction, as no nearby populations exist. The persistence of eastern fox squirrels in this unique habitat is due to synanthropic relationships.

  • Broome, A., Summers, R., & Vanhala, T. (2016) Understanding the provision of conifer seed for woodland species. Forestry Commission Research Note 023. 12 pp.

Abstract: Conifer seed provides an important food resource for many woodland mammals, birds and insects, including some of Britain’s rarest species. This Research Note brings together information from a number of sources on cone and seed production by the main conifers planted in Britain. This information can help managers assess the seed resources of their woodlands and manage the woods for the objective of seed production, whether for food or to encourage natural regeneration. Cone and seed crops fluctuate annually and the amount of seed available in good compared with bad seed years, as well as the frequency of good years, depends on a range of factors which include tree species, age of the crop and climatic conditions. Some species such as Scots pine produce moderate but consistent crops of seed every year, whereas others are much more variable. For example, in a good year Japanese larch can provide the greatest amount of seed and energy per area of woodland of any conifer species grown in Britain, whereas in a poor year production is almost negligible. The time of year when seed is released differs between conifer species. Woodland management can influence the continuity of seed supply as well as the quantities of cones and seed produced. Managing to provide a continuous and abundant seed resource involves consideration of woodland age structure and species composition as well as choice of appropriate interventions.

  • Chavel, E. E., Mazerolle, M. J., Imbeau, L., & Drapeau, P. Comparative evaluation of three sampling methods to estimate detection probability of American red squirrels (Tamiasciurus hudsonicus). Mammalian Biology – Zeitschrift für Säugetierkunde.

Abstract: Measuring changes in species distribution and understanding factors influencing site occupancy are recurring goals in wildlife studies. Imperfect detection of species hinders such studies, resulting in the underestimation of the number of sites occupied by the species of interest. American red squirrels (Tamiasciurus hudsonicus) are sampled traditionally with live-traps that require substantial resources to deploy and monitor. Here, we assessed whether auditory methods yield similar detection probabilities. We compared the detection probability of American red squirrels in boreal forest using point counts, playback counts, and live-trapping. Over the summer of 2014, we conducted three trapping sessions in 60 sites within black spruce forests of northwestern Quebec, Canada. We also conducted 10 min point counts in the same sites, together with playback counts using recordings of American red squirrel alarm and territorial calls. Using dynamic occupancy models to analyse three primary periods, all composed of three secondary periods, we found that the detection probability of squirrels from point counts was as high as with live-trapping. Our results thus highlight the value of the point count method in measuring American red squirrel occupancy.

  • Dylewski, Ł., Przyborowski, T., & Myczko, Ł. (2016) Winter habitat choice by foraging the red squirrel (Sciurus vulgaris). Annales Zoologica Fennici 53: 194-200.

Abstract: The red squirrel (Sciurus vulgaris) is an arboreal species, relatively common in mixed, deciduous and coniferous forests and in urban parks. From autumn to early spring the main diet of red squirrels is seeds in closed conifer cones. In this study, we investigated characteristics of a habitat in western Poland where red squirrels were feeding on Scots pine (Pinus sylvestris). Understory cover, number of tree species, distance to an open area, distance to the nearest great spotted woodpecker (Dendrocopos major) anvil, and size of ten randomly selected Scots pine trees were measured on 70 transects. We used binary logistic regression to test which forest habitat parameters affected the presence of feeding signs of red squirrels. Feeding signs of red squirrels were found from sites close to forest edges with less understory cover, higher tree-species richness and larger size of trees. Red squirrels did not avoid sites close to great spotted woodpecker anvils. We conclude that forest stand structure is important for red squirrel feeding site occurrence, but red squirrels do not avoid close contact to open areas.

  • Fey, K., Hämäläinen, S., & Selonen, V. (2016) Roads are no barrier for dispersing red squirrels in an urban environment. Behavioral Ecology 27: 741-747.

Abstract: In urban environments, roads are one of the major threats for moving animals. Roads can act as barriers to movement either through mortality during crossing attempts or through behavioral avoidance. This can have severe population-level consequences such as population fragmentation and demographic or genetic isolation. A major limitation for determining the effects of roads, however, is the lack of studies on responses of animals to roads during dispersal. In a radiotelemetry study, we investigated the responses of dispersing juvenile red squirrels (Sciurus vulgaris) to roads in an urban environment in Finland. We observed that, during routine movements within their home range, squirrels were located further from roads and crossed them less frequently than simulated random walk paths, while they did not avoid roads when performing explorative and dispersal movements. Moreover, during routine movements squirrels rarely crossed roads with high traffic volume, whereas during dispersal, they crossed both big and small roads. Traffic did not seem to be a major cause of mortality for juvenile squirrels, based on our observations. Our study provides striking evidence that movement behavior during dispersal differs from that of nondispersers. For road ecology, this implies that the evaluation of the role of roads as barriers for, for example, gene flow cannot be based on the interpretation of movements of nondispersers.

  • Goldstein, E., Butler, F. & Lawton, C. (2016) Modeling future range expansion and management strategies for an invasive squirrel species. Biological Invasions.

Abstract: Successful management of an invasive species requires in depth knowledge of the invader, the invaded ecosystem, and their interactions. The complexity of the species-system interactions can be reduced and represented in ecological models for better comprehension. In this study, a spatially explicit population model was created using the RAMAS software package to simulate the past and future  invasion dynamics of the eastern grey squirrel (Sciurus carolinensis) in the fragmented habitat in case study areas in Ireland. This invasive squirrel species causes economic damage by bark stripping forest crops and is associated with the decline of its native congener (S. vulgaris). Three combinations of demographic and dispersal parameters, which best matched the distribution of the species shortly after introduction, were used to simulate invasion dynamics. Future population expansion was modeled under scenarios of no control and two different management strategies: fatal culls and immunocontraceptive vaccination programmes. In the absence of control, the grey squirrel range is predicted to expand to the south and southwest of Ireland endangering internationally important habitats, vulnerable forest crops, and the native red squirrel. The model revealed that region-wide intensive and coordinated culls would have the greatest impact on grey squirrel populations. Control strategies consisting solely of immunocontraceptive vaccines, often preferred by public interest groups, are predicted to be less effective. Complete eradication of the grey squirrel from Ireland is not economically feasible and strategic evidence-based management is required to limit further range expansion. Ecological models can be used to choose between informed management strategies based on predicted outcomes.

  • Gwinn, R., & Koprowski, J. (2016) Differential response to fire by introduced and endemic species complicates endangered species conservation. Hystrix, the Italian Journal of Mammalogy 27(2): n/a-n/a. DOI:

Abstract: Fire is a natural component of, and serves as a tool for, the restoration of forested ecosystems worldwide; however, disturbance due to fire also has been implicated in the proliferation of invasive species. How these fires affect occupancy and use of the forest by wildlife is of great concern, in particular, the differential response of non-native and native species. In the North American Southwest, prior to European settlement, frequent wildfires helped to maintain forest structure. We examined the effect of a large wildfire on an introduced population of the Abert’s squirrel (Sciurus aberti) that has invaded the high elevation forests inhabited by the critically endangered Mt. Graham red squirrel (Tamiasciurus fremonti grahamensis). We found that introduced Abert’s squirrels were more common than native red squirrels in burned areas. Abert’s squirrels did not abandon burned areas but nested, foraged, and did not adjust their home range size in burned areas. This suggests that invasive Abert’s squirrels are better able to exploit burned areas than native red squirrels and that fire can favor non-native species. This interaction between non-native species, native species, and fire adds new insight into the complexities of conservation and restoration of ecosystems and helps to inform conservation activities worldwide.

  • Hyslop, L. (2016) Like rabbit, but sweeter’: the verdict on eating squirrel The Telegraph, 04 April 2016.
  • Jessen, T. G., Kilanowski, A. L., Gwinn, R. N., Merrick, M. J., & Koprowski, J. L. (2016) Microsciurus flaviventer (Rodentia: Sciuridae). Mammalian Species 48: 59-65.

Abstract: Microsciurus flaviventer (Gray, 1867) is a Neotropical tree squirrel commonly known as the Amazon dwarf squirrel. Small bodied with dark brown dorsal pelage contrasted with a gray or yellowish gray venter, and a faintly banded tail. M. flaviventer is 1 of 4 species in the genus Microsciurus. The geographic range of M. flaviventer extends from the Amazon basin of South America throughout western and southeastern Colombia, Ecuador, southern Peru, Brazil west of Río Negro, and Madeira. It is most commonly associated with evergreen lowland tropical rainforest. Status of M. flaviventer is “Data Deficient” under the International Union for Conservation of Nature and Natural Resources Red List of Threatened Species; however, loss of habitat is a major concern.

  • Koprowski, J., Gavish, L., & Doumas, S. (2016) Sciurus anomalus (Rodentia: Sciuridae). Mammalian Species 48: 48-58.

Abstract: Sciurus anomalus Güldenstädt, 1785 is a rodent commonly called the Caucasian squirrel.  S. anomalus is a medium-sized  squirrel with chestnut gray to grizzled buff dorsum, buff eye rings, and chestnut to buff-yellow underparts.  S. anomalus is 1 of 28  species in the genus  Sciurus and is found in forests of the Middle East and extreme southwestern Asia. The International Union for  Conservation of Nature and Natural Resources considers  S. anomalus to be a species of “Least Concern;” habitat destruction is the  main threat.

  • Koprowski, J., Goldstein, E., Bennett, K., & Pereira, C. (2016) Family Sciuridae (Tree, Flying and Ground Squirrels, Chipmunks, Prairie Dogs and Marmots). In D. WIlson, T. Lacher & R. Mittermeier (eds) Handbook of the Mammals of the World – Volume 6: Lagomorphs and Rodents 1. Lynx Edicions in association with Conservation International and IUCN.
  • Lioy, S., Mori, E., Wauters, L. A., & Bertolino, S. (2016) Weight operated see-saw feeding hoppers are not selective for red squirrels when greys are present. Mammalian Biology – Zeitschrift für Säugetierkunde

Abstract: The competition for food resources between the native red squirrel and the introduced American Eastern grey squirrel is well known, and can lead to the extinction of the native species. Providing supplementary food resources for the red squirrel, by adopting selective feeding hoppers, has been proposed as a possible support for the short term conservation of native populations, but studies that investigate its effectiveness have not yet been performed. In this study we evaluate the effectiveness of the feeding hoppers, in terms of selectivity towards the smaller native species, quantifying their utilization by the two species in sympatry and allopatry. Feeding hoppers were not selective toward the native species. The success in the attempts to enter the hoppers was 95% for red and 86% for grey squirrels. The 50 hazelnuts provided during each feeding session, covering the energetic requirements of an individual for 6 (reds) or 3.5 (greys) days, were consumed in 45:43 ± 38:26 hh:mm by red and 31:07 ± 37:18 hh:mm by grey squirrels. The average weight of grey squirrels that entered the feeding hopper (490 ± 47 g) was higher than the calibration weight of the see-saw floor (400 g). This highlights that weight operated see-saw feeding hoppers are poorly selective. Structural modification of the feeding hoppers should be considered to obtain a real selectivity according to species before their implementation in the conservation of red squirrel populations. However feeding hoppers were selective in feeding squirrels when using hazelnuts, excluding the access to food supplies by other species. Therefore they can be used with success in supplementary feeding studies or behavioural and ecological studies, especially if combined with camera traps and individually marked animals.

  • Krishna, M. C., Kumar, A., Tripathi, O. P., & Koprowski, J. L. (2016) Diversity, Distribution and Status of Gliding Squirrels in Protected and Non-protected Areas of Eastern Himalayas in India. 2016, 27. doi:10.4404/hystrix-27.2-11688.

Abstract: The tropical forests of South and Southeast Asia hold the highest gliding squirrel diversity but our knowledge of species diversity, ecology and major threats is limited. The present study was undertaken in Arunachal Pradesh, Northeast India between June 2011 and March 2015 to address the paucity of data available on gliding squirrels. Based on field and literature surveys, 14 species of gliding squirrels were detected in the state of Arunachal Pradesh. However, species such as Biswamoyopterus biswasi , which is reported as endemic to Namdapha National Park, were not detected. The high gliding squirrel diversity in this region could be related to a diversity of forest types and its location between the Himalayas and the Indomalayan region. Encounter rates with four different species revealed that Petaurista petaurista was most frequently detected in Namdapha National Park. Major threats include hunting for traditional medicine, cultural purposes or bushmeat, and habitat loss due to forest degradation caused by shifting cultivation. In addition, more intensive studies on population, ecology and conservation status are needed in order to design species and site specific conservation action plans in this region which represents the highest diversity of gliding squirrels globally.

  • Lurz, P., Shuttleworth, C. & Gurnell, J. (2016) Which trees help red squirrels? Westmorland Red Squirrel Society Newsletter, 6-8.
  • Mazzamuto, M. V., Bisi, F., Wauters, L. A., Preatoni, D. G., & Martinoli, A. (2016) Interspecific competition between alien Pallas’s squirrels and Eurasian red squirrels reduces density of the native species. Biological Invasions  1-13. doi:10.1007/s10530-016-1310-3.

Abstract: When alien species introduced into a new environment have a strong niche overlap with ecologically similar native species, interspecific competition can cause a decrease in abundance and distribution of native species. Pallas’s squirrel (Callosciurus erythraeus) was introduced in Northern Italy where it currently co-occurs with native Eurasian red squirrels (Sciurus vulgaris). The alien species is known for its invasiveness but so far negative effects of Pallas’s squirrels on native tree squirrels have not been demonstrated. Here, we compare demographic parameters of red squirrel populations between sites without (red-only sites) and with (red-Pallas’s sites) C. erythraeus and present results of trapping and removal of Pallas’s squirrel and its effects on red squirrel population dynamics. The native species was patchily distributed and absent in many trapping sites occupied by the Pallas’s squirrel. Red squirrels occurred at much lower densities and showed reduced adult survival in areas of co-occurrence than in red-only sites, but there were no differences in reproductive rate. Removing invasive squirrels throughout the study period resulted in re-colonisation by the native species only in some trapping sites, and several alternatives to explain the lack of a marked increase in population size are discussed. This study is the first to provide evidence that presence of Pallas’s squirrel reduces viability of local red squirrel populations.

  • Merrick, M. J., & Koprowski, J. L. (2016) Evidence of natal habitat preference induction within one habitat type. Proceedings of the Royal Society B: Biological Sciences 283.

Abstract: Natal habitat preference induction (NHPI) is a mechanism for habitat selection by individuals during natal dispersal. NHPI occurs in wild animal populations, and evidence suggests it may be a common, although little studied, mechanism for post-dispersal habitat selection. Most tests of NHPI examine the influence of distinct, contrasting natal habitat types on post-dispersal habitat selection. We test the hypothesis that NHPI can occur within a single habitat type, an important consideration for habitat specialists. The Mount Graham red squirrel (Tamiasciurus hudsonicus grahamensis) is an endangered forest obligate restricted to a single mountain primarily within mixed-conifer forest. We test for NHPI by comparing intra-individual differences in natal and settlement habitat structure and composition to expected random pairwise differences. Dispersing juveniles appear to select settlement locations that are more similar to natal areas than expected in several forest structure and composition variables that include canopy cover and live basal area. Our results provide support for NHPI as a mechanism for post-dispersal habitat selection in habitat specialists that occupy a single vegetation community type.

  • Rocha, R. G., Leite, Y. L. R., Costa, L. P., & Rojas, D. (2016) Independent reversals to terrestriality in squirrels (Rodentia: Sciuridae) support ecologically mediated modes of adaptation. Journal of Evolutionary Biology 29: 2471-2479. doi:10.1111/jeb.12975.

Abstract: The family Sciuridae is one of the most widespread and ecologically diverse lineages of rodents and represents an ideal model for investigating the evolution of locomotion modes and the historical biogeography of terrestrial mammals. We used a comprehensive database on locomotion modes, an updated phylogeny and novel biogeographic comparative methods to reassess the evolution of locomotion of squirrels and to investigate whether these locomotion modes evolved convergently in different continents. We found that locomotion changes occurred in different independent lineages of the family, including four reversals to terrestriality and one evolution of gliding. We also found evidence for Eurasia as the centre of origin of Sciuridae, challenging the classification of the oldest squirrel fossil records from the early Oligocene in North America. Additionally, Eurasia is also the possible centre of origin for most of squirrel subfamilies and tribes, and where locomotion changes have occurred. Parallel locomotion shifts could be explained by the adaptation towards different ecological niches followed by colonization of new continents.

  • Selonen, V., Varjonen, R., & Korpimäki, E. (2016) Predator presence, but not food supplementation, affects forest red squirrels in winter. Annales Zoologica Fennici 53: 183-193.

Abstract: We studied the responses of red squirrels, Sciurus vulgaris, to food supplementation and avian predation risk during two winters in Finland, when the level of natural food production, spruce seeds, varied markedly. We performed an open experiment with 6 replicates in the landscape where squirrel signs were counted near a feeding station and/or active predator nest and control site. Within each site, we counted squirrel snow-tracks and feeding-signs and checked the usage of two nest-boxes. We observed that during the winter when natural food was less plentiful, red squirrel snow-tracks decreased at sites with predator. The same was observed, only less clearly, during the winter with more natural food. Food supplementation had no obvious effect. We conclude that predators have a clear effect on red squirrels in winter. Furthermore, in situations where a species is specialized in using fluctuating amounts of natural food resources, the role of artificial food supplementation may remain unclear.

  • Selonen, V. & Wistbacka, R. (2016) Siberian flying squirrels do not anticipate future resource abundance. BMC Ecology 16:51. doi:10.1186/s12898-016-0107-7.

Abstract: One way to cope with irregularly occurring resources is to adjust reproduction according to the anticipated future resource availability. In support of this hypothesis, few rodent species have been observed to produce, after the first litter born in spring, summer litters in anticipation of autumn’s seed mast. This kind of behaviour could eliminate or decrease the lag in population density normally present in consumer dynamics. We focus on possible anticipation of future food availability in Siberian flying squirrels, Pteromys volans. We utilise long-term data set on flying squirrel reproduction spanning over 20 years with individuals living in nest-boxes in two study areas located in western Finland. In winter and early spring, flying squirrels depend on catkin mast of deciduous trees. Thus, the temporal availability of food resource for Siberian flying squirrels is similar to other mast-dependent rodent species in which anticipatory reproduction has been observed.

  • Selonen, V., Wistbacka, R., & Korpimäki, E. (2016) Food abundance and weather modify reproduction of two arboreal squirrel species. Journal of Mammalogy 97: 1376-1384.

Abstract: The importance of weather in relation to food resources, in determining reproduction, remains poorly understood for mammals, particularly for species that do not depend on food resources limited by spring weather conditions. We studied the effects that weather and food supply had on timing of spring reproduction and observed litter size in 2 squirrel species, the Siberian flying squirrel and the European red squirrel, using long-term data sets spanning 20–30 years. Both species subsist on foods from tree masting, and these are available for squirrels from autumn until early spring. Good food conditions in winter and spring before reproduction had positive effects on spring reproduction in both species by advancing the onset of reproduction, and in flying squirrels, slightly increasing litter size. Higher temperature in late winter and, surprisingly, increased precipitation in late winter resulted in early reproduction in flying squirrels and red squirrels, respectively. In addition, higher early spring temperature was positively related to litter size in red squirrels, likely reflecting low survival of small juveniles in cold weather. Our study supports the view that spring reproduction in these species is determined by food supply before breeding. Our results also highlight the fact that reproduction is also dependent on weather.

  • Selonen, V., Wistbacka, R., & Santangeli, A. (2016) Sex-specific patterns in body mass and mating system in the Siberian flying squirrel. BMC Zoology 1:9.  doi:10.1186/s40850-016-0009-3.

Abstract: Reproductive strategies and evolutionary pressures differ between males and females. This often results in size differences between the sexes, and also in sex-specific seasonal variation in body mass. Seasonal variation in body mass is also affected by other factors, such as weather. Studies on sex-specific body mass patterns may contribute to better understand the mating system of a species. Here we quantify patterns underlying sex-specific body mass variation using a long-term dataset on body mass in the Siberian flying squirrel, Pteromys volans.

  • Signorile, A. L., Lurz, P. W. W., Wang, J., Reuman, D. C., & Carbone, C. (2016) Mixture or mosaic? Genetic patterns in UK grey squirrels support a human-mediated ‘long-jump’ invasion mechanism. Diversity and Distributions 22: 1-12. doi:10.1111/ddi.12424.

Abstract: Aim: Clarifying whether multiple introductions of a species remain relatively isolated or merge and interbreed is essential for understanding the dynamics of invasion processes. Multiple introductions from different sources can result in a mixture of genetically distinct populations, increasing the total genetic diversity. This mixing can resolve the ‘genetic paradox’, whereby in spite of the relatively small numbers of introduced individuals, the augmented diversity due to this mixing increases adaptability and the ability of the species to spread in new environments. Here, we aim to assess whether the expansion of a successful invader, the Eastern grey squirrel, was partly driven by the merger of multiple introductions and the effects of such a merger on diversity. Location: UK, Ireland. Methods: We analysed the genetic variation at 12 microsatellite loci of 381 individuals sampled from one historical and 14 modern populations of grey squirrels. Results: Our data revealed that current UK population structure resembles a mosaic, with minimal interpopulation mixing and each element reflecting the genetic make-up of historic introductions. The genetic diversity of each examined population was lower than a US population or a historical UK population. Numbers of releases in a county did not correlate with county-level genetic diversity. Inbreeding coefficients remain high, and effective population sizes remain small. Main conclusions: Our results support the conclusion that rapid and large-scale expansion in this species in the UK was not driven by a genetic mixing of multiple introduced populations with a single expansion front, but was promoted by repeated translocations of small propagules. Our results have implications for the management of grey squirrels and other invasive species and also demonstrate how invaders can overcome the genetic paradox, if spread is facilitated by human-mediated dispersal.

  • Tagliacozzo, A., Fiore, I., Rolfo, M., & Salari, L. (2016) New data on Late Pleistocene and Holocene red squirrel, Sciurus vulgaris L., 1758, in Italy. Revue de Paleobiologie 35: 417-445.

Abstract: The genus Sciurus is known since Late Miocene in the European fossil record, but it is quite rare. Fossil remains of squirrels occur in relatively few sites and generally with very few specimens, sometimes only one or two teeth. Recent finds of a Sciurus vuslgaris mandible from Grotta Mora Cavorso (Latium), and the reanalysis of the red squirrel remains from the Caverna delle Arene Candide (Liguria), the Riparo Soman (Veneto) and the Grotta del Santuario della Madonna (Calabria) provide new data and insights on the change in size of the rodent and on its geographic and ecological distribution in the Pleistocene and Holocene of Italy. The study of food preferences of the current red squirrel predators provides solid comparative data to measure the relative rarity of the bone remains found in the Late Pleistocene and Holocene paleontological deposits and archaeological contexts. Taphonomic analysis, particularly on the latest Pleistocene remains from the Caverna delle Arene Candide, sheds light on the alimentary and cultural use of the rodent made by prehistoric man, allowing to say that so far the human contribution to the accumulation of his bones has been underestimated.

  • Turkia, T., Selonen, V. & Brommer, J.E.  (2016) Large-scale spatial synchrony in red squirrel ( Sciurus vulgaris ) sex ratios. Journal of Mammalogy 97: 744-752.

Abstract: Large-scale studies on population-level sex ratios are few, even though sex ratio is an important determinant of population viability and dynamics. Mechanisms driving large-scale sex ratio variation include spatially autocorrelated resources and scale differences in local versus global Fisherian feedback of the operational sex ratio. In this study, we reanalyze historic data on sex ratios based on 187,404 hunted subadult and adult red squirrels ( Sciurus vulgaris ) capturing spatial sex ratio variation in 50×50 km squares throughout Finland over a period of 8 years. Overall, sex ratio was slightly male biased (50.9%) and relatively more 50×50 km squares showed a bias toward males (19% of squares) compared to females (8% of squares). Sex ratio was spatially autocorrelated at distances up to 200 km and in some years showed a U-shaped pattern: regions that were in close proximity and those that were far apart had similar sex ratios, but regions in-between had opposite sex ratios. We found no evidence that food supply (spruce cone crop) drives regional red squirrel sex ratio. Our findings add to the scarce evidence that vertebrate sex ratios show spatial patterns over large scales.

  • Tye, C. A., McCleery, R. A., Fletcher, R. J., Greene, D. U., & Butryn, R. S. (2016) Evaluating citizen vs. professional data for modelling distributions of a rare squirrel. Journal of Applied Ecology n/a-n/a. doi:10.1111/1365-2664.12682.

Abstract: * To realize the potential of citizens to contribute to conservation efforts through the acquisition of data for broad-scale species distribution models, scientists need to understand and minimize the influences of commonly observed sample selection bias on model performance. Yet evaluating these data with independent, planned surveys is rare, even though such evaluation is necessary for understanding and applying data to conservation decisions. * We used the state-listed fox squirrel Sciurus niger in Florida, USA, to interpret the performance of models created with opportunistic observations from citizens and professionals by validating models with independent, planned surveys. * Data from both citizens and professionals showed sample selection bias with more observations within 50 m of a road. While these groups showed similar sample selection bias in reference to roads, there were clear differences in the spatial coverage of the groups, with citizens observing fox squirrels more frequently in developed areas. * Based on predictions at planned field surveys sites, models developed from citizens generally performed similarly to those developed with data collected by professionals. Accounting for potential sample selection bias in models, either through the use of covariates or via aggregating data into home range size grids, provided only slight increases in model performance. * Synthesis and applications. Despite sample selection biases, over a broad spatial scale opportunistic citizen data provided reliable predictions and estimates of habitat relationships needed to advance conservation efforts. Our results suggest that the use of professionals may not be needed in volunteer programmes used to determine the distribution of species of conservation interest across broad spatial scales.

  • Uchida, K., Suzuki, K., Shimamoto, T., Yanagawa, H. & Koizumi, I. (2016) Seasonal variation of flight initiation distance in Eurasian red squirrels in urban versus rural habitat. Journal of Zoology 298: 225-231.

Abstract: Urbanization has caused significant behavioural modifications in wild animals. Change in anti-predator behaviour is the most widespread example across different taxa in urban areas, which is probably due to a decrease in predation pressure and habituation towards humans. Seasonality or phenology has also been modified by urbanization since some resources in urban environments are highly controlled, for example, artificial feeding. Under natural conditions, anti-predator responses vary with seasonal variability in environmental and individual conditions. However, resource stability possibly reduces the seasonality of anti-predator behaviours in urban animals. Here, we compare the seasonal difference of flight initiation distance (FID), a measurement of anti-predator response, in Eurasian red squirrels Sciurus vulgaris between urban and rural areas in the Tokachi region, Hokkaido, Japan. Rural squirrels possessed FIDs two to three times longer than those of urban squirrels. We also found squirrels in rural areas lowered FID in autumn, but no seasonal difference was observed in urban squirrels. Our results suggest that continuous supplementary feeding may have buffered the seasonality in anti-predator response. In addition, strong habituation to humans may allow urban red squirrels to correctly assess human activity as benign rather than reacting unnecessarily.

  • Xiao, Z., & Zhang, Z. (2016) Contrasting patterns of short-term indirect seed–seed interactions mediated by scatter-hoarding rodents. Journal of Animal Ecology n/a-n/a. doi:10.1111/1365-2656.12542.

Abstract: * It is well known that direct effects of seed predators or dispersers can have strong effects on seedling establishment. However, we have limited knowledge about the indirect species interactions between seeds of different species that are mediated by shared seed predators and/or dispersers and their consequences for plant demography and diversity. Because scatter-hoarding rodents as seed dispersers may leave some hoarded seeds uneaten, scatter hoarding may serve to increase seed survival and dispersal. Consequently, the presence of heterospecific seeds could alter whether the indirect interactions mediated by scatter-hoarding rodents have a net positive effect, creating apparent mutualism between seed species, or a net negative effect, creating apparent competition between seed species. * We present a testable framework to measure short-term indirect effects between co-occurring plant species mediated by seed scatter-hoarding rodents. We tested this framework in a subtropical forest in south-west China using a replacement design and tracked the fate of individually tagged seeds in experimental patches. We manipulated the benefits to rodents by using low-tannin dormant chestnuts as palatable food and high-tannin non-dormant acorns as unpalatable food. * We found that seed palatability changed the amount of scatter hoarding that occurred when seeds co-occurred either among or within patches. Consistent with our predictions, scatter-hoarding rodents created apparent mutualism through increasing seed removal and seed caching, and enhancing survival, of both plant species in mixed patches compared with monospecific patches. However, if we ignore scatter hoarding and treat all seed harvest as seed predation (and not dispersal), then apparent competition between palatable chestnuts and unpalatable acorns was also observed. * This study is the first to demonstrate that foraging decisions by scatter-hoarding animals to scatter hoard seeds for later consumption (or loss) or consume them can influence indirect effects among co-occurring seeds, and rodent-mediated indirect effects vary depending on whether the harvested seeds are hoarded or eaten.


  • Blythe, R. M., Lichti, N. I., Smyser, T. J., & Swihart, R. K. (2015) Selection, caching, and consumption of hardwood seeds by forest rodents: implications for restoration of American chestnut. Restoration Ecology 23: 473-481.

Abstract: ecent field trials on blight-resistant hybrids (BC3F3) of American chestnut (Castanea dentata) and Chinese chestnut (C. mollissima) have intensified planning for widespread restoration of Castanea to eastern U.S. forests. Restoration will likely rely on natural seed dispersal from sites planted with chestnut; however, we do not know how dispersal agents such as granivorous rodents will respond to hybrid chestnuts. At one extreme, excessive seed consumption may impede restoration. Alternatively, scatter-hoarding rodents might facilitate the spread of chestnut by dispersal of seeds from restoration plantings. We conducted trials with five rodent species to quantify foraging preferences and to evaluate the potential role of granivores in chestnut restoration. Specifically, we presented seeds from American and hybrid chestnuts (BC3F2) with other common mast species and recorded the proportion of seeds removed and the fates of tagged seeds. Mice, chipmunks, and flying squirrels harvested both chestnut types preferentially over larger, tougher black walnut, hickory, and red oak seeds, but fox squirrels and eastern gray squirrels preferred larger seeds to chestnuts. All rodents consumed a greater proportion of the chestnuts than other seed types. American and hybrid chestnut also differed in important ways: except for fox squirrels, rodents preferentially removed American chestnuts over hybrid chestnuts, but we estimated that fox squirrels carried a greater proportion of hybrid chestnuts beyond our tag search area, suggesting that hybrids may be dispersed farther and cached more often than American chestnut. These differences indicate that hybrid chestnut may not be functionally equivalent to American chestnut with regard to seed–granivore interactions.

  • Bosch, S., Spiessl, M., Müller, M., Lurz, P. W. W., & Haalboom, T. (2015) Mechatronics meets biology: experiences and first results with a multipurpose small mammal monitoring unit used in red squirrel habitats.  Hystrix 26:

Monitoring is a fundamental aspect of species conservation and research. Technological advances, especially with respect to camera trap technologies, have allowed glimpses into unknown aspects of species behaviour and have the potential to greatly assist species distribution monitoring. Here we present the findings of a pilot study combining existing biological monitoring techniques with mechatronics to advance monitoring technologies and develop a multi-purpose, species specific, automated monitoring system. We developed a Small Mammal Monitoring Unit (SMMU) that integrates automated video, and sound recording, carries out body weight measurements and takes hairs samples with a bait station in a portable perspex box. The unit has the potential for use with a range of small mammal species, but has been field-tested here on red squirrels, Sciurus vulgaris , in Germany, Scotland and Switzerland. We successfully collected hair-samples, body mass data as well as video and sound recordings. Preliminary data analyses also revealed behavioural information. Heavier individuals first gained access to the feeder in the morning and have longer feeding bouts. Our prototype demonstrated that the collaboration between mechatronic and biology offers novel, integrated monitoring techniques for a range of research application. The development of units for other mammal species is planned. Future developments will explore the possibilities for wireless data transmission, built-in collection of weather data and collection of images from inside the unit for the recognition of individuals.

  • Chen, H. & Koprowsk, J. (2015) Animal occurrence and space use change in the landscape of anthropogenic noise. Biologcal Conservation 192: 315-322.

Habitat fragmentation, destruction, and disturbance are major threats to biodiversity. Global road networks represent one of the most significant human impacts on ecosystems, and a spatially extensive source of anthropogenic disturbance and noise. We developed a novel approach by combining traffic monitoring with noise mapping on the basis of a standardized traffic-noise stimulus generated by controlled vehicle operation to investigate temporal and spatial heterogeneity of traffic noise. We used animal presence or absence, radio-telemetric monitoring of space use, and remotely sensed habitat characteristics with occupancy modeling and spatial analysis to assess influences of distance from roads, habitat characteristics, and traffic noise level on site occupancy and space use of Mt. Graham red squirrels (Tamiasciurus hudsonicus grahamensis). Traffic noise had spatially extensive and negative effects on site occupancy. Animal occurrence decreased as traffic noise increased after accounting for distance from roads. Traffic noise levels in animal core home ranges were lower than noise levels within total home ranges. Our study disentangled effects of traffic noise from confounding environmental characteristics and demonstrated the chronic impacts of traffic noise on animal distribution. We highlight the importance of incorporating spatial and temporal heterogeneity of traffic noise at a local scale when investigating effects of anthropogenic noise on wildlife.

  • Dozières, A., Pisanu, B., Kamenova, S., Bastelica, F., Gerriet, O. & Chapuis, J-L. (2015) Range expansion of Pallas’s squirrel (Callosciurus erythraeus) introduced in southern France: habitat suitability and space use. Mammalian Biology – Zeitschrift für Säugetierkunde.

Abstract: The study of space use and population density in different habitats is an important step in understanding the expansion process of an introduced species and in gathering useful knowledge for management actions. Pallas’s squirrel (Callosciurus erythraeus) was introduced on the Cap d’Antibes (southeastern France) at the end of the 1960s. We used direct observations from a grid map centered onto the known historical distribution to document the expanding range of Pallas’s squirrel. We assessed habitat suitability in the invaded area through distance sampling and nest counts and examined space use by quantifying the size of the home range and intra- and inter-sexual overlap based on radio-tracking in a suitable habitat. Our results confirm that Pallas’s squirrel has expanded its range exponentially over the past two decades, although with low diffusion coefficients (0.08–0.20 km/yr). Squirrels reached the highest relative densities in suburban woodlands, in which females showed no territorial behaviour. Our results indicate that Pallas’s squirrel was able to establish in various habitats in Antibes, preferentially in woodlands and gardens. Densely urbanised areas and the presence of the highway A8 (E80) acted as barriers that slowed range expansion. Such information is crucial to improve the control program started in 2012 to limit the spread of this potentially invasive squirrel.

  • Goldstein, E., Butler, F., & Lawton, C. (2015) Frontier population dynamics of an invasive squirrel species: Do introduced populations function differently than those in the native range? Biological Invasions 17: 1181-1197. doi:10.1007/s10530-014-0787-x.

Abstract: Several squirrel species are biological invaders and their establishment in an area is often marked by ecological and economic costs to native species and forest crops. The eastern grey squirrel (Sciurus carolinensis Gmelin 1788) has been intentionally introduced multiple times outside of its native range but its success in establishing and spreading has not been consistent. An intensive live-trapping programme was designed to investigate the demography and population dynamics of populations of this species on the invasion frontier in the Republic of Ireland, a region marked by the slow but steady invasion of the grey squirrel. Low densities and high breeding rates distinguished these frontier populations. These results were placed in context with other frontier and established grey squirrel populations throughout their introduced and native ranges. As expected, variations in invasion speed and impact severity between regions were reflected in population demography. The highest densities, survival rates and breeding rates were recorded in Britain where the grey squirrel invasion has been most damaging. Careful comparative demographic study of invading populations could improve management outcomes, indicate differential invasibility of invaded communities, and offer clues to enhance the design of conservation reintroduction projects

  • Guichón, M. L., Benetiz, V., V, Gozzi, A. C., Hertzriken, M., & Borgnia, M. (2015) From a lag in vector activity to a constant increase of translocations: invasion of Callosciurus squirrels in Argentina. Biological Invasions 17: 2597-2604.

Abstract: Arboreal squirrels of the Asiatic genus Callosciurus have shown high likelihood of establishment from few released animals, in particular, C. erythraeus has established wild populations in Argentina, Belgium, France, Hong Kong, Japan, and The Netherlands. We report the invasion process of C. erythraeus in Argentina in the last four decades and suggest management actions for each foci. Between February 2011 and November 2014 we conducted field surveys and interviews in nine sites in central Argentina to confirm the presence of C. erythraeus, describe their history of introduction, and estimate range expansion and squirrel relative abundance. We report a two decades lag-phase until the onset of translocations of C. erythraeus within national boundaries that resulted in a constant increase of the cumulative number of releases. We confirm nine new release events between 1995 and 2012 and six new invasion foci that yields a total of 13 deliberate releases and 10 invasion foci established in rural and urban areas of Argentina. Spread rate ranged from 0.12 to 0.66 km/year. An intermediate relative density of squirrels (2–7 ind/ha) was found close to release sites except in one case. All introduction events involved squirrels translocated from the first, 40 years old invasion focus, occasionally involving illegal trade. The rate of introduction events in the last decades and the translocation-lag phase described in this study should call the attention in all countries dealing with charismatic, introduced species. Translocation disruption requires urgent attention to slow down the invasion of this and other species.

  • Haigh, A.,O’Riordan, R. & Butler, F. (2015) The preference for yew (Taxus baccata) by a red (Sciurus vulgaris) only squirrel population. Wildlife Research 42: 426-436.

Abstract: Context: As invasive grey squirrels continue to spread, red only areas are becoming rarer. It has been reported that red squirrels can outcompete greys only in pure coniferous woodland. In areas of sympatry with grey squirrels, there are concerns about red squirrels’ dependence on certain coniferous tree species in light of recent tree diseases.
Aims: This study aimed to investigate tree selection by red squirrels in an area vulnerable to the spread of the grey squirrel, but currently free of this species.
Methods: During 2013–14, squirrels were trapped and monitored on a 315-ha managed island, with a woodland characterised by a mixture of deciduous and coniferous species. Radio-tracking revealed that squirrels clustered their activity along a network of yew trees, a preference they showed throughout the year. Trap success was also higher in traps placed on yew trees. Yew and beech were selected most commonly, but squirrels were also observed foraging on other items, such as sycamore flowers and lichen. Squirrels spent 35% of their time foraging, utilising the greatest number of tree species in June (n = 13). In spring, squirrels foraged to a greater extent on the ground than in the trees, and exploited a lower number of tree species.
Conclusions: There has been little previous data on the use of yew trees by red squirrels, but they have previously been listed as a species that is preferred by red squirrels rather than greys. This study has further emphasised the importance of this tree species to red squirrels.
Implications: The continued spread of the grey squirrel may lead to red squirrels becoming restricted to areas of intense management such as parks and, accordingly, optimum tree planting is required from the onset for the long-term maintenance of red squirrels. With recent concern about the disease vulnerability of other coniferous species, this study emphasises the relative importance of yew and other tree species in the distribution of red squirrels.

  • Holmes, M. (2015) The perfect pest: natural history and the red squirrel in nineteenth-century Scotland. Archives of Natural History 42: 113-125.

Abstract: Following the extirpation of the red squirrel from much of Scotland by the end of the eighteenth century, nineteenth-century naturalists strived to find evidence of its native Scottish status. As medieval accounts and Gaelic place names proved ambiguous, the true extent of the squirrel’s former habitat was a matter of some debate. While numerous reintroductions of the species were made from the late eighteenth century, general enthusiasm for the return of the squirrel quickly turned to dismay, ultimately followed by persecution. If the squirrel originally represented a symbolic mission to rediscover a lost species, the physical animal itself fell below expectations. It became publically perceived as both economically and ecologically destructive. The squirrel was despised by foresters and landowners for damaging trees, while naturalists condemned the species for the destruction of bird’s eggs and nests. This article will investigate naturalists’ quests to rediscover the red squirrel, before examining changing attitudes to the species upon its reintroduction and gradual proliferation. The narrative will emerge through the works and correspondence of Scottish naturalist John Alexander Harvie-Brown (1844–1916) and The new statistical account of Scotland. (1834–1845). The argument will be made that the red squirrel as an object of antiquarian curiosity initially made the species endearing to natural historians, as part of a wider fascination with extinct British fauna. However, the clash between naturalists’ established ornithological interests did little to endear the species to that community, leaving the red squirrel open to a policy of general persecution on economic grounds

  • Lane J.E., McAdam A.G., Charmantier A., Humphries M.M., Coltman D.W., Fletcher Q., Gurrell, J.C. & Boutin, S. (2015) Post-weaning parental care increases fitness but is not heritable in North American red squirrels. Journal of Evolutionary Biology  28:1203-12.

Abstract: Most empirical attempts to explain the evolution of parental care have focused on its costs and benefits (i.e., fitness consequences). In contrast, few investigations have been made of the other necessary prerequisite for evolutionary change, inheritance. Here, we examine the fitness consequences and heritability (h2) of a post-weaning parental care behaviour (territory bequeathal) in a wild population of North American red squirrels. Each year, a subset (average across all years = 19%) of reproductive females bequeathed their territory to a dependent offspring. Bequeathing females experienced higher annual reproductive success and did not suffer a survival cost to themselves relative to those females retaining their territory. Bequeathing females thus realized higher relative annual fitness (ω = 1.18 ± 0.03 (SE)) than non-bequeathing females (ω = 0.96 ± 0.02 (SE)). Additive genetic influences on bequeathal behaviour, however, were not significantly different from 0 (h2 = 1.9 x 10-3; 95% Highest Posterior Density Interval = 3.04 x 10-8 to 0.37) and, in fact, bequeathal behaviour was not significantly repeatable (R = 2.0 x 10-3; 95% HPD interval = 0 to 0.27). In contrast, directional environmental influences were apparent. Females were more likely to bequeath in years following low food abundance and when food availability in the upcoming autumn was high. Despite an evident fitness benefit, a lack of heritable genetic variance will constrain evolution of this trait.

  • Lucas, J. M., Prieto, P. & Galián, J. (2015) Red squirrels from south–east Iberia: low genetic diversity at the southernmost species distribution limit. Animal Biodiversity and Conservation 38: 129-138.

Abstract: Red squirrels from southeast Iberia: low genetic diversity at the southernmost species distribution limit.— South–east Iberia is the southernmost limit of this species in Europe. Squirrels in the region mainly inhabit coniferous forests of Pinus. In this study, we analyzed the pattern of mitochondrial genetic variation of southern Iberian red squirrels. Fragments of two mitochondrial genes, a 350–base pair of the displacement loop (D–loop) and a 359–bp of the cytochrome b (Cytb), were sequenced using samples collected from 88 road–kill squirrels. The genetic variation was low, possibly explained by a recent bottleneck due to historical over–exploitation of forest resources. Habitat loss and fragmentation caused by deforestation and geographic isolation may explain the strong genetic subdivision between the study regions. Six new haplotypes for the D–loop and two new haplotypes for the Cytb fragments are described. A Cytb haplotype of south–east Iberia was found to be present in Albania and Japan, suggesting local extinction of this haplotype in intermediate areas. No significant clustering was found for the south–east of Spain or for the other European populations (except Calabria) in the phylogenetic analysis.

  • Macpherson, M. F., Davidson, R. S., Duncan, D. B., Lurz, P. W., Jarrott, A., & White, A. (2015) Incorporating habitat distribution in wildlife disease models: conservation implications for the threat of squirrelpox on the Isle of Arran. Animal Conservation n/a-n/a.

Abstract: Emerging infectious diseases are a substantial threat to native populations. The spread of disease through naive native populations will depend on both demographic and disease parameters, as well as on habitat suitability and connectivity. Using the potential spread of squirrelpox virus (SQPV) on the Isle of Arran as a case study, we develop mathematical models to examine the impact of an emerging disease on a population in a complex landscape of different habitat types. Furthermore, by considering a range of disease parameters, we infer more generally how complex landscapes interact with disease characteristics to determine the spread and persistence of disease. Specific findings indicate that a SQPV outbreak on Arran is likely to be short lived and localized to the point of introduction allowing recovery of red squirrels to pre-infection densities; this has important consequences for the conservation of red squirrels. More generally, we find that the extent of disease spread is dependent on the rare passage of infection through poor quality corridors connecting good quality habitats. Acute, highly transmissible infectious diseases are predicted to spread rapidly causing high mortality. Nonetheless, the disease typically fades out following local epidemics and is not supported in the long term. A chronic infectious disease is predicted to spread more slowly but can remain endemic in the population. This allows the disease to spread more extensively in the long term as it increases the chance of spread between poorly connected populations. Our results highlight how a detailed understanding of landscape connectivity is crucial when considering conservation strategies to protect native species from disease threats.

  • Millins, C., Magierecka, A., Gilbert, L., Edoff, A., Brereton, A., Kilbride, E., et al. (2015) An invasive mammal (grey squirrel, Sciurus carolinensis) commonly hosts diverse and atypical genotypes of the zoonotic pathogen Borrelia burgdorferi sensu lato. Applied and Environmental Microbiology 

Abstract: Invasive vertebrate species can act as hosts for endemic pathogens and may alter pathogen community composition and dynamics. For the zoonotic pathogen Borrelia burgdorferi sensu lato, the agent of Lyme borreliosis, recent work shows invasive rodent species can be of high epidemiological importance and may support host specific strains. This study examined the role of grey squirrels (Sciurus carolinensis), (n=679), an invasive species in the United Kingdom (UK), as B. burgdorferi s.l. hosts. We found that grey squirrels were frequently infested with Ixodes ricinus, the main vector of B. burgdorferi s.l. in the UK, and 11.9% were infected with B. burgdorferi s.l. All four genospecies which occur in the UK were detected in grey squirrels, and unexpectedly, the bird associated genospecies B. garinii, was most common. The second most frequent infection was with B. afzelli. Genotyping of B. garinii and B. afzelli produced no evidence for strains associated with grey squirrels. Generalised linear mixed models (GLMM) identified tick infestation and date of capture as significant factors associated with B. burgdorferi s.l. infection in grey squirrels, with infection elevated in early summer in squirrels infested with ticks. Invasive grey squirrels appear to become infected with locally circulating strains of B. burgdorferi s.l., further studies are required to determine their role in community disease dynamics. Our findings highlight that the role of introduced host species in B. burgdorferi s.l epidemiology can be highly variable and thus difficult to predict.

  • Mori, E., Mazzoglio, P., Rima, P., Aloise, G., & Bertolino, S. (2015) Bark-stripping damage by Callosciurus finlaysonii introduced into Italy. Mammalia 

Abstract: The Finlayson’s squirrel Callosciurus finlaysonii was introduced into Italy during the 1980s and has established two viable populations. The diet of this species includes a high proportion of tree barks, suggesting an intensive debarking behavior. We reported a severe bark-stripping impact in both colonized areas, and we tested whether a preference for some tree species existed. Results of this work showed the presence of a wide spectrum of damaged species, without any strong preference, mainly with large wounds. Old deciduous plants and conifers, which presented a hard bark, were usually avoided.

  • Palmer, R.R. & Koprowski, J.L. (2015) How do Neotropical pygmy squirrels (Sciurillus pusillus) use seasonally flooded forests in the Peruvian Amazon? Journal of Mammalogy.

Abstract: Tree squirrels are important components of ecosystems but to understand their role, we must learn how squirrels select and use habitat. Tree squirrel species richness is highest in the tropics and, according to the International Union for Conservation of Nature, is also where the greatest number of data deficient species occurs. The Neotropical pygmy squirrel (Sciurillus pusillus) is one of these species. In 2009 and 2010, we conducted distance sampling to estimate population density, we measured vegetation variables to investigate forest characteristics that influence habitat selection at 3 different scales, and conducted observations to obtain knowledge about activity patterns and behavior of Neotropical pygmy squirrels in igapó forest in the Peruvian Amazon. Density of squirrels was 0.10 and 0.14 individuals/ha, respectively, for each year. Squirrel activity peaked at 0800h, individuals were found mainly in the canopy and never on the ground, and frequency of squirrel behaviors differed by time and story level. Squirrels mainly used high and low restinga and areas that had more trees that were ≥ 30cm diameter at breast height (DBH)/ha compared to random areas in our site in igapó forest. Squirrels used trees that were larger in DBH, taller, and had a larger live crown compared to random trees. Neotropical pygmy squirrels are associated with features related to mature forests.

  • Pečnerová, P., Moravec, J.C., & Martínková, N. (2015)  A skull might lie: modelling ancestral ranges and diet from genes and shape of tree squirrels.. Systematic Biology 64: 1074-88.

Abstract: Tropical forests of Central and South America represent hotspots of biological diversity. Tree squirrels of the tribe Sciurini are an excellent model system for the study of tropical biodiversity as these squirrels disperse exceptional distances, and after colonizing the tropics of the Central and South America, they have diversified rapidly. Here, we compare signals from DNA sequences with morphological signals using pictures of skulls and computational simulations. Phylogenetic analyses reveal step-wise geographic divergence across the Northern Hemisphere. In Central and South America, tree squirrels form two separate clades, which split from a common ancestor. Simulations of ancestral distributions show western Amazonia as the epicenter of speciation in South America. This finding suggests that wet tropical forests on the foothills of Andes possibly served as refugia of squirrel diversification during Pleistocene climatic oscillations. Comparison of phylogeny and morphology reveals one major discrepancy: Microsciurus species are a single clade morphologically but are polyphyletic genetically. Modelling of morphology-diet relationships shows that the only group of species with a direct link between skull shape and diet are the bark-gleaning insectivorous species of Microsciurus. This finding suggests that the current designation of Microsciurus as a genus is based on convergent ecologically-driven changes in morphology.

  • Posthumus E,Koprowski J, Steidl R (2015) Red squirrel middens influence abundance but not diversity of other vertebrates. PLoS One 10: e0123633.

Abstract: Some animals modify the environment in ways that can influence the resources available to other species. Because red squirrels (Tamiasciurus hudsonicus) create large piles of conifer-cone debris (middens) in which they store cones, squirrels concentrate resources that might affect biodiversity locally. To determine whether other animals are attracted to midden sites beyond their affinity for the same resources that attract red squirrels, we assessed associations between middens, mammals, and birds at population and community levels. We surveyed 75 middens where residency rates of red squirrels varied during the previous five years; sampling along this residency gradient permitted us to evaluate the influence of resources at middens beyond the influence of a resident squirrel. At each location, we quantified vegetation, landscape structure, abundance of conifer cones, and midden structure, and used capture-recapture, distance sampling, and remote cameras to quantify presence, abundance, and species richness of mammals and birds. Red squirrels and the resources they concentrated at middens influenced mammals and birds at the population scale and to a lesser extent at the community scale. At middens with higher residency rates of red squirrels, richness of medium and large mammals increased markedly and species richness of birds increased slightly. After accounting for local forest characteristics, however, only species richness of medium-to-large mammals was associated with a red squirrel being resident during surveys. In areas where red squirrels were resident during surveys or in areas with greater amounts of resources concentrated by red squirrels, abundances of two of four small mammal species and two of four bird species increased. We conclude that the presence of this ecosystem modifier and the resources it concentrates influence abundance of some mammals and birds, which may have implications for maintaining biodiversity across the wide geographic range inhabited by red squirrels and other larderhoarding animals.

  • Ramos-Lara N, Koprowski J (2015) Spacing behavior of a non-larder-hoarding Tamiasciurus: a study of Mearns’s squirrels in xeric coniferous forests. Ethology 121: 196-205.

Abstract: In ecosystems with seasonal fluctuations in food supply many species use two strategies to store food: larder hoarding and scatter hoarding. However, because species at different geographic locations may experience distinct environmental conditions, differences in hoarding behavior may occur. Tree squirrels in the genus Tamiasciurus display variation in hoarding behavior. Whereas red (Tamiasciurus hudsonicus) and Douglas’s (Tamiasciurus douglasii) squirrels in mesic coniferous forests defend territories centered around larder hoards maintaining non-overlapping home ranges, red squirrels in deciduous forests defend small scatter-hoarded caches of cones maintaining overlapping home ranges. As in other rodent species, variation in hoarding behavior appears to influence the spacing behavior of red and Douglas’s squirrels. In contrast, Mearns’s squirrels (Tamiasciurus mearnsi) in xeric coniferous forests neither rely on larder hoards nor appear to display territorial behavior. Unfortunately, little is known about the ecology of this southernmost Tamiasciurus. Using radiotelemetry, we estimated home-range size, overlap, and maximum distance traveled from nest to examine the spacing behavior of Mearns’s squirrels. Similar to scatter-hoarding rodents, maximum distance traveled from nest was greater for males during mating season, whereas those of females were similar year round. Although no seasonal differences were detected, male home ranges were three times larger during mating season, whereas those of females were smaller and displayed a minor variation between seasons. Home ranges were overlapped year round but contrary to our expectations, overlap was greater during mating season for both sexes, with no detectable relationship between male home-range size and the number of females overlapped during mating season. Overall, the results appear to support our hypothesis that in the absence of larder hoards, the spacing behavior of Mearns’s squirrels should be different from larderhoarding congeners and more similar to scatter-hoarding rodents.

  • Romeo, C., Ferrari, N., Lanfranchi, P., Saino, N., Santicchia, F., Martinoli, A., et al. (2015) Biodiversity threats from outside to inside: effects of alien grey squirrel (Sciurus carolinensis) on helminth community of native red squirrel (Sciurus vulgaris). Parasitology Research 114: 2621-2628. doi:10.1007/s00436-015-4466-3.

Abstract: Biological invasions are among the major causes of biodiversity loss worldwide, and parasites carried or acquired by invaders may represent an added threat to native species. We compared gastrointestinal helminth communities of native Eurasian red squirrels (Sciurus vulgaris) in the presence and absence of introduced Eastern grey squirrels (Sciurus carolinensis) to detect alterations induced by the alien species. In particular, we investigated whether spillover of a North American nematode Strongyloides robustus occurs and whether prevalence of a local parasite Trypanoxyuris sciuri in red squirrels is affected by grey squirrel presence. The probability of being infected by both parasites was significantly higher in areas co-inhabited by the alien species, where 61 % of examined red squirrels (n = 49) were infected by S. robustus and 90 % by T. sciuri. Conversely, in red-only areas, the two parasites infected only 5 and 70 % of individuals (n = 60). Overall, our findings support the hypothesis that red squirrels acquire S. robustus via spillover from the alien congener and suggest that invaders’ presence may also indirectly affect infection by local parasites through mechanisms diverse than spill-back and linked to the increased competitive pressure to which red squirrels are subjected. These results indicate that the impact of grey squirrel on red squirrels may have been underestimated and highlight the importance of investigating variation in macroparasite communities of native species threatened by alien competitors.

  • Sanamxay, D., Douangboubpha, B., Bumrungsri, S., Satasook, C., & Bates Paul, J. J. (2015) A summary of the taxonomy and distribution of the red giant flying squirrel, Petaurista petaurista (Sciuridae, Sciurinae, Pteromyini), in mainland Southeast Asia with the first record from Lao PDR. Mammalia 79: 305-314.

Abstract: The occurrence of the red giant flying squirrel, Petaurista petaurista, in Lao PDR is confirmed on the basis of a single adult male specimen obtained from an informal food market in Thatlouang village, Xekong Province in the south of the country. This individual was reported to have been collected from close-by Thatlouang in the mixed deciduous forest or dry dipterocarp forest on the Bolaven Plateau. The record extends the known distribution of this species by approximately 700 km eastwards. Information is provided on the external, cranial, dental, and bacular characters of the new Lao specimen. It is compared with the holotypes and/or type descriptions of seven taxa, namely, barroni, candidula, cicur, melanotus, penangensis, taylori, and terutaus, described from mainland Southeast Asia, all of which are currently included in the synonymy of P. petaurista. On the basis of its external pelage colour, the Lao specimen is referred to P. p. barroni, which was described from southeast Thailand and is considered here to be a valid subspecies.

  • Santicchia. F.,Romeo C., Grilli, G., Vezzoso, S., Wauters,  L.A., Mazzamuto, M., et al. (2015) The use of uterine scars to explore fecundity levels in invasive alien tree squirrels. Hystrix 26:

Abstract: In invasion ecology, reliable measures of female fecundity are necessary to infer population growth rate and develop control programs to determine the proportion of animals that should be culled to reduce population size. Here, we present a reliable staining technique of uterine scars to determine individual fecundity in terms of both seasonal and total (annual) number of young born per female. We applied this method to two alien squirrels species (grey squirrel, Sciurus carolinensis and Pallas’s squirrel, Callosciurus erythraeus) introduced in Northern Italy, obtaining carcasses from control campaigns from 2011 to 2013. We also investigated environmental and phenotypic variables that might affect individual variation in fecundity and compared annual reproductive output between the two species. For grey squirrels (n=44), 25% of examined females produced a single litter and 61% two litters. Females which reproduced in both seasons tended to have larger summer than spring litters (on average 2.61 and 1.94 offspring, respectively) and mean annual fecundity was 3.4 scars/female ranging from 1 to 8 births. There was no effect of year, eye lens weight, body size or body mass on total fecundity. For Pallas’s squirrel (n=31), 58% of females had a spring litter, some of these also produced a summer litter (35%) and a few even a third litter in autumn (10%). Heavier and older females (higher eye lens weight) had more uterine scars than younger animals with lower body mass. Finally, fecundity of the two IAS in Italy was similar or even higher than in the native range and/or in other countries of introduction, suggesting they are well adapted to their new environment and potentially have a high capacity to spread and recover after reduction of population size.

  • Santicchia, F., Romeo, C., Martinoli, A., Lanfranchi, P., Wauters, L. A., & Ferrari, N. (2015) Effects of habitat quality on parasite abundance: do forest fragmentation and food availability affect helminth infection in the Eurasian red squirrel? Journal of Zoology 296:38-44.

Abstract: Habitat quality affects demography, population genetics, space use and phenotypic characteristics of mammals. However, little is known about the effects of habitat quality, fragmentation and/or food abundance, on host–parasite interactions. Here we present a first study on the relationships between the abundance of the dominant gastrointestinal helminth, Trypanoxyuris (Rodentoxyuris) sciuri, infecting the Eurasian red squirrel Sciurus vulgaris and three environmental factors: habitat type (mountain conifer forests vs. lowland mixed deciduous forests), fragmentation (fragmented woodlands vs. continuous forests) and food availability. Abundance of T. (R.) sciuri increased in fragmented woods. Furthermore, in mountain conifer forests, squirrels were more heavily infected after a poor Norway spruce seed crop than in years with medium or high seed production, indicating that squirrels are less capable of reducing parasite load when food availability is low. Hence, we suggest that T. (R.) sciuri abundance in red squirrels may be determined mainly by changes in host susceptibility induced by higher stress levels and/or poorer nutritional status, while in fragments, reduced genetic diversity may also increase host susceptibility to parasite infection. Although our data do not shed light on the mechanisms generating the observed patterns, results from other field studies highlighted the effect of stress and nutritional status on parasite infection, thus suggesting their implication in the changes in the abundance of T. (R.) sciuri.

  • Selonen, V., Varjonen, R. & Korpimäki, E. (2015) Immediate or lagged responses of red squirrel population to pulsed resources. Oecologia 177: 401-411.

According to producer-consumer models, consumers should follow pulsed resources with a time lag. This view has been challenged by studies demonstrating that individuals may anticipate future resource pulses by increasing reproduction just before the pulse. We studied population fluctuations and reproduction in European red squirrels, Sciurus vulgaris, in relation to seed masting of the main food resource (the Norway spruce) in boreal coniferous forests between 1979 and 2013. Red squirrels are pre-dispersal seed predators, and previous studies have shown that they can anticipate the coming seed mast. We did not find any indication that anticipation of masting (year t ) increased red squirrel reproduction in the preceding spring to early summer. Instead, the reproductive output of the squirrels was highest in the spring following the mast, indicating that the population had to be at its largest size in the autumn after the mast (year(t+1)), when lots of subadults were around. However, we surmised, based on snow tracks and squirrel nest data, that the population crashed during the following winter (year(t+1)). These data reflected the adult population during winter, which peaked at the same time as the resource pulse. We can therefore conclude that the time lag between the resource pulse and the attainment of the peak number of squirrels was less than one year, and that the resource crash affected more juveniles and subadults than adults. The population increase overlapped with the occurrence of masting, but there was also a lagged response, supporting the classical view of producer-consumer models.

  • Shuttleworth, C., Halliwell, E., & Lurz, P. W. W. (2015) Squirrel projects. European Squirrel Initiative, Woodbridge, Suffolk UK.
  • Shuttleworth, C., Lurz, P., & Hayward, M. (2015) Red Squirrels: Ecology, Conservation & Management in Europe, 328 pp. European Squirrel Initiative, Woodbridge, Suffolk UK.
    • Bertolino, S., Martinoli, A., Paoloni, D., Marsan, A., & Wauters, L. (2015) The grey squirrel in Italy: impacts and management. In C. Shuttleworth, P. Lurz & M. Hayward (eds) Red Squirrels: Ecology, Conservation & Management in Europe, 163-173. European Squirrel Initiative, Woodbridge, Suffolk UK.
    • Everest, D., Shuttleworth, C., Grierson, S., Dastjerdi, A., Stidworthy, M., Duff, J., et al. (2015) The impact of adenoviruses on red squirrel (Sciurus vulgaris) conservation – with notes on other enteric viruses of potential significance. In C. Shuttleworth, P. Lurz & M. Hayward (eds) Red Squirrels: Ecology, Conservation & Management in Europe, 129-146. European Squirrel Initiative, Woodbridge, Suffolk UK.
    • Gurnell, J., Blackett, T., Butler, H., Lurz, P., Magris, L., & Shuttleworth, C. (2015) British red squirrel strongholds: challenges for conservation. In C. Shuttleworth, P. Lurz & M. Hayward (eds) Red Squirrels: Ecology, Conservation & Management in Europe, 213-232. European Squirrel Initiative, Woodbridge, Suffolk UK.
    • Gurnell, J., Lurz, P., & Wauters, L. (2015) Years of interactions and conflict in Europe: competition between Eurasian red squirrels and North American grey squirrels. In C. Shuttleworth, P. Lurz & M. Hayward (eds) Red Squirrels: Ecology, Conservation & Management in Europe. European Squirrel Initiative, Woodbridge, Suffolk UK.
    • Halliwell, E., Shuttleworth, C., Wilberforce, E., Denman, H., Lloyd, C., & Cartmel, S. (2015) Striving for success: an evaluation of local action to conserve red squirrels (Sciurus vulgaris) in Wales. In C. Shuttleworth, P. Lurz & M. Hayward (eds) Red Squirrels: Ecology, Conservation & Management in Europe, 176-192. European Squirrel Initiative, Woodbridge, Suffolk UK.
    • Jayne, K., & Leaver, L. (2015) Strategic decisions made by small mammals during scatter hoarding, cache recovery and cache pilferage. In C. Shuttleworth, P. Lurz & M. Hayward (eds) Red Squirrels: Ecology, Conservation & Management in Europe, 51-65. European Squirrel Initiative, Woodbridge, Suffolk UK.
    • Krauze-Gryz, D., & Gryz, J. (2015) A review of the diet of the red squirrel (Sciurus vulgaris) in different types of habitats. In C. Shuttleworth, P. Lurz & M. Hayward (eds) Red Squirrels: Ecology, Conservation & Management in Europe, 39-50. European Squirrel Initiative, Woodbridge, Suffolk UK.
    • Lawton, C., Waters, C., & Shuttleworth, C. (2015) Reintroductions and translocations of red squirrels within Europe. In C. Shuttleworth, P. Lurz & M. Hayward (eds) Red Squirrels: Ecology, Conservation & Management in Europe, 193-212. European Squirrel Initiative, Woodbridge, Suffolk UK.
    • Lurz, P., Bertolino, S., Koprowski, J., Willis, P., Tonkin, M., & Gurnell, J. (2015) Squirrel monitoring: snapshots of population presence and trends to inform management. In C. Shuttleworth, P. Lurz & M. Hayward (eds) Red Squirrels: Ecology, Conservation & Management in Europe, 279-297. European Squirrel Initiative, Woodbridge, Suffolk UK.
    • McInnes, C., Deane, D., & Fiegna, C. (2015) Squirrelpox virus: origins and the potential for its control. In C. Shuttleworth, P. Lurz & M. Hayward (eds) Red Squirrels: Ecology, Conservation & Management in Europe, 251-264. European Squirrel Initiative, Woodbridge, Suffolk UK.
    • Meredith, A., & Romeo, C. (2015) Disease and causes of mortality in red squirrel populations. In C. Shuttleworth, P. Lurz & M. Hayward (eds) Red Squirrels: Ecology, Conservation & Management in Europe, 116-127. European Squirrel Initiative, Woodbridge, Suffolk UK.
    • Sage, R., & Sotherton, N. (2015) Predation of woodland bird nests by tree squirrels in Britain Central Europe and North America. In C. Shuttleworth, P. Lurz & M. Hayward (eds) Red Squirrels: Ecology, Conservation & Management in Europe, 147-162. European Squirrel Initiative, Woodbridge, Suffolk UK.
    • Selonen, V., & Hanski, I. (2015) Occurrence and dispersal of the red squirrel and the Siberian flying squirrel in fragmented landscapes. In C. Shuttleworth, P. Lurz & M. Hayward (eds) Red Squirrels: Ecology, Conservation & Management in Europe, 67-82. European Squirrel Initiative, Woodbridge, Suffolk UK.
    • Seward, A., & O’Hare, S. (2015) The importance of community support and participation for regional red squirrel conservation: a case study from northern England. In C. Shuttleworth, P. Lurz & M. Hayward (eds) Red Squirrels: Ecology, Conservation & Management in Europe, 299-316. European Squirrel Initiative, Woodbridge, Suffolk UK.
    • Sheehy, E., & Lawton, C. (2015) Predators of red and grey squirrels in their natural and introduced ranges. In C. Shuttleworth, P. Lurz & M. Hayward (eds) Red Squirrels: Ecology, Conservation & Management in Europe, 83-96. European Squirrel Initiative, Woodbridge, Suffolk UK.
    • Shuttleworth, C., Lurz, P., Hayward, M., & Bertolino, S. (2015) Developing Integrated Red Squirrel Conservation in Europe. In C. Shuttleworth, P. Lurz & M. Hayward (eds) Red Squirrels: Ecology, Conservation & Management in Europe, 317-328. European Squirrel Initiative, Woodbridge, Suffolk UK.
    • Shuttleworth, C., Schuchert, P., Everest, D., McInnes, C., Rushton, S., Jackson, N., et al. (2015) Developing integrated and applied red squirrel conservation programmes: What lessons can Europe learn from a regional grey squirrel eradication programme in North Wales? In C. Shuttleworth, P. Lurz & M. Hayward (eds) Red Squirrels: Ecology, Conservation & Management in Europe, 233-250. Woodbridge, Suffolk UK, European Squirrel Initiative.
    • Signorile, L., Wang, J., Reuman, D., Bertolino, S., & Lurz, P. (2015) How population genetics can contribute to the management of grey squirrel invasions. In C. Shuttleworth, P. Lurz & M. Hayward (eds) Red Squirrels: Ecology, Conservation & Management in Europe, 97-113. European Squirrel Initiative, Woodbridge, Suffolk UK.
    • White, A., Lurz, P., Jones, H., Boots, M., Bryce, J., Tonkin, M., et al. (2015) The use of mathematical models in red squirrel conservation: Assessing the threat from grey invasion and disease to the Fleet basin stronghold. In C. Shuttleworth, P. Lurz & M. Hayward (eds) Red Squirrels: Ecology, Conservation & Management in Europe, 265-277. European Squirrel Initiative, Woodbridge, Suffolk UK.
  • Simpson, V., Hargreaves, J., Butler, H., Blackett, T., Stevenson, K., & McLuckie, J. (2015) Leprosy in red squirrels on the Isle of Wight and Brownsea Island. Veterinary Record 177: 206-207. doi:10.1136/vr.h4491.
  • Stevenson-Holt, C. D. & Sinclair, W. (2015) Assessing the geographic origin of the invasive grey squirrel using DNA sequencing: Implications for management strategies. Global Ecology and Conservation 3: 20-27.

Abstract: The invasive grey squirrel Sciurus carolinensis has become a major pest species causing negative effects to forestry and biodiversity. This study aims to assess the origin of grey squirrel within Cumbria using phylogeographic analysis to aid in management and control. The work reported analysed mitochondrial DNA sequences in the D-Loop gene of 73 grey squirrel individuals from multiple locations in the UK. The results indicate that individuals in north Cumbria are derived from individuals from Scotland and North East England. Other individuals in north Cumbria share a unique haplotype with south Cumbria and Lancashire suggesting a southerly origin and movement around or over the Cumbrian Mountain range which is thought of as a barrier to movements. The assessment of invasive species geographical origin and the identification of potential wildlife transit corridors through natural barriers are becoming more important as species shift range in response to environmental and ecological changes. With the grey squirrel population expansion also occurring in Italy, the European red squirrel may become threatened across its entire range. It is crucial to understand the population origins of the invasive grey squirrel and landscape usage to successfully manage the incursion routes and control the population.

  • Studd, E. K., Boutin, S, McAdam, AG, Krebs, C.J. & Humphries, M.M. (2015). Predators, energetics and fitness drive neonatal reproductive failure in red squirrels. Journal of Animal Ecology 84: 249-259.


* Neonatal reproductive failure should occur when energetic costs of parental investment outweigh fitness benefits. However, little is known about the drivers of neonatal reproductive failure in free-ranging species experiencing continuous natural variation in predator abundance and in the energetic and fitness costs and benefits associated with parental investment.

* Long-term comprehensive studies are required to better understand how biotic, abiotic and life-history conditions interact to drive occurrences of reproductive failure in the wild.

* Using 24 years (1987–2011) of reproductive data from a northern boreal population of North American red squirrels in south-western Yukon, we examined the effects of predator abundance, energetics (resource availability, ambient temperature and litter size) and fitness benefits (probability of overwinter juvenile survival and maternal age) on occurrences of neonatal reproductive failure (494/2670 reproductive attempts; 18·5%).

* Neonatal reproductive failure was driven by a combination of predator abundance, and the energetic and fitness costs and benefits of parental investment. The abundance of mustelids and maternal age was positively related to the occurrence of neonatal reproductive failure. High energy costs associated with a combination of low resource availability and cold ambient temperatures or large litters, corresponded to increased occurrences of neonatal reproductive failure. However, the strength of these relationships was influenced by variation in juvenile overwinter survival (i.e. fitness benefits).

* We provide evidence that predation pressure is an important driver of neonatal reproductive failure. In addition, we found a trade-off occurs between resource-dependent energetic and fitness costs and benefits of raising the current litter to independence.

  • Uchida, K., Suzuki, K., Shimamoto, T., Yanagawa, H., & Koizumi, I. (2015) Seasonal variation of flight initiation distance in Eurasian red squirrels in urban versus rural habitat. Journal of Zoology, n/a-n/a. doi:10.1111/jzo.12306.

Abstract: Urbanization has caused significant behavioural modifications in wild animals. Change in anti-predator behaviour is the most widespread example across different taxa in urban areas, which is probably due to a decrease in predation pressure and habituation towards humans. Seasonality or phenology has also been modified by urbanization since some resources in urban environments are highly controlled, for example, artificial feeding. Under natural conditions, anti-predator responses vary with seasonal variability in environmental and individual conditions. However, resource stability possibly reduces the seasonality of anti-predator behaviours in urban animals. Here, we compare the seasonal difference of flight initiation distance (FID), a measurement of anti-predator response, in Eurasian red squirrels Sciurus vulgaris between urban and rural areas in the Tokachi region, Hokkaido, Japan. Rural squirrels possessed FIDs two to three times longer than those of urban squirrels. We also found squirrels in rural areas lowered FID in autumn, but no seasonal difference was observed in urban squirrels. Our results suggest that continuous supplementary feeding may have buffered the seasonality in anti-predator response. In addition, strong habituation to humans may allow urban red squirrels to correctly assess human activity as benign rather than reacting unnecessarily.

  • Vieira, B., Fonseca, C., & Rocha, R. (2015) Critical steps to ensure the successful reintroduction of the Eurasian red squirrel. Animal Biodiversity and Conservation 38: 49-58.

Abstract: Critical steps to ensure the successful reintroduction of the Eurasian red squirrel.— Wildlife reintroduction strategies aim to establish viable long–term populations, promote conservation awareness and provide economic benefits for local communities. In Portugal, the Eurasian red squirrel (Sciurus vulgaris) became extinct in the 16th century and was reintroduced in urban parks in the 1990s, mainly for aesthetic and leisure purposes. We evaluated the success of this reintroduction in two urban parks and here described the critical steps. We assessed habitat use, population density and abundance, and management steps carried out during reintroduction projects. Reintroductions have been successful to some extent given squirrels are present 20 years after release. However, populations in both parks are declining due to the lack of active management and poor quality habitat. Successful reintroduction of Eurasian red squirrel in areas without competition of alien tree squirrels involves three critical main stages. The pre–project stage includes studies on habitat quality, genetic proximity between donors and closest wild population, and health of donor stocks. In the release stage, the number of individuals released will depend on resource variability, and the hard release technique is an effective and economically viable method. Post–release activities should evaluate adaptation, mitigate mortality, monitor the need for supplementary feeding, provide veterinary support, and promote public awareness and education.

  • Wilson, D. R., Goble, A. R., Boutin, S., Humphries, M. M., Coltman, D. W., Gorrell, J. C., et al. (2015) Red squirrels use territorial vocalizations for kin discrimination. Animal Behaviour 107: 79-85.

Abstract: The ability to discriminate among individuals, or among classes of individuals, can provide animals with important fitness benefits. Although several mechanisms for discrimination are possible, most require animals to show stable phenotypic variation that reflects their identity or their membership in a particular class (e.g. sex, mate, kin). For territorial animals that rarely interact physically, vocalizations could serve as long-distance signals that facilitate discrimination. In this study, we tested whether the territorial rattle vocalizations of North American red squirrels, Tamiasciurus hudsonicus, are repeatable, and whether they could hence provide the basis for multiple types of discrimination. We measured four structural features from two rattles from each of 76 marked squirrels. All four features were repeatable, which is consistent with territorial rattles being individually distinctive. We then conducted a playback experiment to determine whether squirrels use rattles for discrimination. Specifically, we tested whether squirrels discriminate between the rattles of neighbours and non-neighbours, and kin (coefficient of relatedness, r ≥ 0.25) and non-kin (r &lt; 0.125). Following a 2 × 2 factorial design, we broadcast a rattle from a non-neighbouring nonkin individual to 15 subjects, from a neighbouring nonkin individual to 14 subjects, from a non-neighbouring kin individual to 11 subjects, and from a neighbouring kin individual to 13 subjects. Subjects did not discriminate between the rattles of neighbours and non-neighbours, but did respond differently to the rattles of kin and nonkin. Specifically, squirrels were significantly more likely to produce a rattle of their own in response to the broadcasted rattles of nonkin versus the broadcasted rattles of kin. This result demonstrates that red squirrels can use territorial vocalizations for kin discrimination. It also suggests that they are more tolerant of territorial intrusions by kin.

  • Yi, X. & Wang, Z. (2015) Dissecting the roles of seed size and mass in seed dispersal by rodents with different body sizes. Animal Behaviour 107: 263-267.

Abstract: The process of seed dispersal is influenced by animals’ responses to seeds with different traits. Seed size/mass is one of the key seed traits affecting animal-mediated seed dispersal. Although seed size is usually positively correlated with seed mass, it is not clear whether the two seed traits show similar effects on seed choice and seed dispersal by animals. In the present study, we artificially manipulated nuts of Juglans mandshurica to create two types of seeds: (1) seeds of the same size but different mass and (2) seeds of the same mass but different size. Our aim was to explore whether food-hoarding animals respond differently to seed size and mass. Our results showed that seed size was more important than seed mass in determining seed removal by wood mice, Apodemus peninsulae. However, the larger red squirrels, Sciurus vulgaris, evaluated seed profitability based on mass rather than size. Moreover, seed mass showed consistent positive effects on seed dispersal distances of J. mandshurica by both A. peninsulae and S. vulgaris. Our results indicate that the effects of seed size and mass on seed dispersal processes are not always consistently correlated. In addition, seed dispersers of different size show different responses to given seed traits such as size or mass. More effort should be made to investigate the role of seed traits and seed dispersers in seed dispersal systems.

  • Zelditch, M.L.,Li, J.,Tran L.A.P. & Swiderski, D.L. (2015) Relationships of diversity, disparity and their evolutionary rates in squirrels (Sciuridae). Evolution 69:1284-1300.

Abstract: Several theories predict that rapidly diversifying clades will also rapidly diverge phenotypically; yet, there are also reasons for suspecting that diversification and divergence might not be correlated. In the widely distributed squirrel clade (Sciuridae), we test for correlations between per-lineage speciation rates, species richness, disparity and a time-invariant measure of disparity that allows for comparing rates when evolutionary modes differ, as they do in squirrels. We find that species richness and speciation rates are not correlated with clade age or with each other. Disparity appears to be positively correlated with clade age because young, rapidly diversifying Nearctic grassland clades are strongly pulled to a single stable optimum but older, slowly diversifying Paleotropical forest clades contain lineages that diverge along multiple ecological and morphological lines. That contrast is likely due to both the environments they inhabit and their phylogenetic community structure. Our results argue against a shared explanation for diversity and disparity in favor of geographically mediated modes of speciation and ecologically mediated modes of phenotypic evolution.


  • Ball, S.J., Daszak, P., Sainsbury, A.W. & Snow, K.R. (2014) Coccidian parasites of red squirrels (Sciurus vulgaris) and grey squirrels (Sciurus carolinensis) in England. Journal of Natural History 1-6.
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  • Bakker, V.J.& Van Vuren, D.H. (2004) Gap-crossing decisions by the Red Squirrel, a forest-dependent small mammal.Conservation Biology 18: 689-697.
  • Gurnell, J. (2004) Grey Squirrels Invade Europe. Mammals UK. Mammals Trust UK, London
  • Gurnell,J., Lurz, P.W.W., Shirley, M.D.F., Cartmel, S., Garson, P.J., Magris, L., & Steele, J. (2004) Monitoring red (Sciurus vulgaris) and grey (Sciurus carolinensis) squirrels in Britain. Mammal Review 34: 51-74.
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  • Anon (2003)Urban grey squirrels. DEFRA Rural Develeopment Setrvices Technical Advisory Note WM09 [PDF]
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  • Desrochers, A., Hanski, I. K. & Selonen, V. (2003) Siberian flying squirrel responses to high- and low- contrast forest edges.Landscape Ecology 18:543-552.
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  • Tompkins, D., Sainsbury, A.W., Netteleton, P., Buxton, D. & Gurnell. J. (2002) Parapoxvirus causes a deleterious disease of red squirrels associated with UK population declines.Proceedings of the Royal Society of London 269: 529-533.
  • Verbeylen, G., De Bruyn, L. & Matthysen, E. (2003) Patch occupancy, population density and dynamics in a fragmented red squirrel Sciurus vulgaris population. Ecography 26, 118-128.


  • Barr, J. J., Lurz, P. W. W., Shirley, M. D. F. & Rushton, S. P. (2002) Evaluation of immunocontraception as a publicly acceptable form of vertebrate pest species control: the introduced grey squirrel in Britain as an example. Environmental Management, 30, 342-351.
  • Bertolini,S; Genovesi,P (2002) Spread and attempted eradication of the grey squirrel (Sciurus carolinensis) in Italy, and consequences for the red squirrel (Sciurus vulgaris) in Eurasia.Biological Conservation 109, 351-358.
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  • Gurnell, J., Cartmel, S., Lurz, P.W.W. & Rushton, S.P. (2002)Modelling the effects of forest composition and management on conserving red squirrels in Clocaenog Forest, North Wales.Unpublished Report for Forestry Commission and Countryside Council for Wales.
  • Gurnell, J. & Steele, J. (2002) Grey Squirrel Control for Red Squirrel Conservation – Thetford Forest. Published Report for English Nature and the Forestry Commission.
  • Gurnell, J., Clark, M.J., Lurz, P.W.W., Shirley, M.D.F. & Rushton, S.P. (2002) Conserving red squirrels (Sciurus vulgaris): mapping and forecasting habitat suitability using a Geographic Information Systems Approach. Biological Conservation 105: 53-64.
  • Koprowski, J.L. (2002) Handling tree squirrels with an efficient and safe restraint. Wildlife Society Bulletin 30:101-103.
  • Kurtila,M; Pukkala,T; Loikkanen,J (2002) The performance of alternative spatial objective types in forest planning calculations: a case for flying squirrel and moose. Forest Ecology and Management 166, 245-260.
  • Lee,TH (2002) Feeding and hoarding behaviour of the Eurasian red squirrel Sciurus vulgaris during autumn in Hokkaido, Japan.Acta theriologica 147, 459-470.
  • Magris, L. & Gurnell, J. (2002) Population ecology of the red squirrel (Sciurus vulgaris) in a fragmented woodland ecosystem on the Island of Jersey, Channel islands. Journal of Zoology, London 256: 99-112.
  • McAdam,AG; Boutin,S; R‚ale,D; Berteaux,D (2002) Maternal effects and the potential for evolution in a natural population of animals. Evolution 56, 846-851.
  • Schauffert, C., J. Koprowski, V. Greer, M. Alanen & K. Hutton. (2002) Potential predators of Mt. Graham red squirrels.Southwestern Naturalist 47:498-501.
  • Wauters, L.A., Tosi, G. & Gurnell, J. (2002) Interspecific competition of grey on reds: do grey squirrels deplete tree seeds cached by red squirrels. Behavioral Ecology and Sociobiology 51:360-367
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    • Gurnell, J. (2001) Red squirrels: a species in decline. Mammals UK Summer 2001 Pp7-8, Mammals Trust UK, London.
    • Gurnell, J., Lurz, P.P.W. & Pepper, H. (2001) Practical techniques for surveying and monitoring squirrels. Forestry Commission Practice Note 11. Forestry Commission, Edinburgh. 12pp.
    • Gurnell, J. , Wauters, L.A., Preatoni, D. & Tosi, G. (2001) Spacing behaviour, kinship and dynamics of the grey squirrel in a newly colonised deciduous woodland in north Italy. Canadian Journal of Zoology 79: 1533-1543.
    • Hale, M. L., Peter W.W. Lurz, Mark D.F. Shirley, Steven Rushton, Robin M. Fuller & Kirsten Wolff (2001). The Impact of Landscape Management on the Genetic Structure of Red Squirrel Populations. Science 293: 2246-2248.
    • Koprowski, J.L. & M.C. Corse (2001) Food habits of Chiricahua Fox Squirrels (Sciurus nayaritensis chiricahuae). Southwestern Naturalist, 46:62-65.
    • Lurz, P.W.W., Rushton, S.P., Wauters, L.A., Bertolino, S., Corrado, I., Mazzoglio, P. & Shirley, M.D.F. (2001). Predicting gray squirrel expansion in North Italy: a spatially explicit modelling approach. Landscape Ecology , 16, 407-420
    • Sainsbury, A.W., Adair, B., Graham, D., Gurnell, J., Cunningham, A.A., Benko, M. & Papp, T. (2001) Isolation of a novel adenovirus associated with splenitis, diarrhoea, and mortality in translocated red squirrels, Sciurus vulgaris. Verh. ber. Ekrg. Zootiere 40: 265-270.

Selonen, V., Hanski, I. K & Stevens, P. (2001) Space use of Siberian flying squirrel Pteromys volans in fragmented forest landscapes. Ecography 24:588-600.

  • Shuttleworth, C.M. & Gurnell, J. (2001) The management of coastal sand dune woodland for red squirrels (Sciurus vulgaris L.). In Coastal Dune Management: Shared Experience of European Conservation Practice (eds. J.A. Houston, S.E. Edmondson & P.J. Rooney) pp. 117 – 127. Liverpool University Press, Liverpool, England.
  • Steele, M.A. & Koprowski, J.L. (2001) North American Tree Squirrels Smithsonian Institution Press, 201 pp.
  • Wauters, L.A., Gurnell, J., Martinoli, A. & Tosi, G. (2001) Does interspecific competition with grey squirrels affect the foraging behaviour and food choice of red squirrels. Animal Behaviour 61: 1079-1091.
  • Wauters, L.A., Gurnell, J. ,Preatoni, D. & Tosi, G (2001) Effects of spatial variation in food availability on spacing behaviour and demography of Eurasian red squirrels. Ecography 24: 525-538.


  • Bruemmer, C., Lurz, P., Larsen, K. & Gurnell, J. (2000) Impacts and management of the alien Eastern Gray Squirrel in Great Britain and Italy: lessons for British Columbia. Pp. 341 – 349. In L. M. Darling (editor). Proceedings of a Conference on the Biology and Management of Species and Habitats at Risk, Kamloops, B.C., 15 – 19 Feb., 1999. Volume One. B.C. Ministry of Environment, Lands and Parks, Victoria, B.C. and University College of the Cariboo, Kamloops, B.C. 490 pp.
  • Cagnin, M., Aloise, G., Fiore, F., Oriolo, V. & Wauters, L.A. (2000). Habitat use and population densityof the red squirrel, Sciurus vulgaris meridionalis, in the Sila Grande mountain range (Calabria, South Italy). Ital. J. Zool. 67: 81-87.
  • Lurz, P.W.W., Garson, P.J. & Wauters, L.A.. (2000). Effects of temporal and spatial variations in food supply on the space and habitat use of red squirrels, Sciurus vulgaris L. J. Zool., Lond. 251: 167-178.
  • Rushton, S.P., Lurz, P.W.W. & Gurnell, J. (2000) Modelling the spatial dynamics of parapoxvirus disease in red and grey squirrels: a possible cause of the decline in the red squirrel in the United Kingdom? Journal of Applied Ecology 37:1-18.
  • Sainsbury, A.W., Nettleton, P., Gilray, J. & Gurnell, J. (2000) Grey squirrels have high seroprevalence to a parapoxvirus associated with deaths in red squirrels. Animal Conservation 3: 229-233.
  • Verbeylen, G. & De Bruyn, L. (2000). Inventarisatie van de Aziatische grondeekhoorn in De Panne. Een project van het IBW en AMINAL afdeling Natuur. Rapport 3 – September 2000.
  • Wauters, L.A. (2000). Squirrels – Medium-sized Granivores in Woodland Habitats. – In: Halle, S. and Stenseth N. C. (eds), Activity Patterns in Small Mammals: a Comparative Ecological Approach. Ecological Studies 141, Springer-Verlag, Heidelberg, Germany, pp. 131-143.
  • Wauters, L.A., Lurz, P.W.W. & Gurnell, J. (2000). The effects of interspecific competition by grey squirrels (Sciurus carolinensis) on the space use and population dynamics of red squirrels (S. vulgaris) in conifer plantations. Ecological Research 15: 271-284.
  • Teangana, D.Ó., Russ, J.M., Mathers, R.G., & Montgomery, W.I. (2000) Habitat associations of the red squirrel Sciurus vulgaris and grey squirrel S. carolinensis in Northern Ireland. Biology and Environment: Proceedings of the Royal Irish Academy, Vol. 100B, No. 1, 27-33.


  • Barratt, E.M., Gurnell, J., Malarky, G. Deaville, R. & Bruford, M.W. (1999) Genetic structure of fragmented populations of red squirrel (Sciurus vulgaris) in Britain. Molecular Ecology 8: S55-S63.
  • David-Gray, Z.K., Gurnell, J. & Hunt, D.M. (1999) Estimating the relatedness in a population of grey squirrels, Sciurus carolinensis, using DNA fingerprinting. Acta theriologica 44: 243-251.
  • David-Gray, Z.K., Gurnell, J. & Hunt, D.M. (1999) DNA fingerprinting reveals high levels of genetic diversity in British populations of the introduced non-native grey squirrel, Sciurus carolinensis. Journal of Zoology, London 246: 443-486.
  • Gurnell, J. (1999) Grey squirrels in woodlands: managing grey squirrels to prevent woodland damage. Enact 7: 10-14.
  • Gurnell, J. and Wauters, L. (1999) Sciurus vulgaris. In The Atlas of European Mammals. Mitchell-Jones, A.J., Amori, G., Bogdanowicz, W., Krystufek, B., Reijnders, P.J.H., Spitzenberger. F., Stubbe, M., Thissen, J.B.M., Vohohralik, V. & Zima, J. (Eds.) pp. 180-181. Academic press, London.
  • Gurnell, J. and Wauters, L. (1999) Sciurus carolinensis. In The Atlas of European Mammals. Mitchell-Jones, A.J., Amori, G., Bogdanowicz, W., Krystufek, B., Reijnders, P.J.H., Spitzenberger. F., Stubbe, M., Thissen, J.B.M., Vohohralik, V. & Zima, J. (Eds.) pp. 178-179. Academic press, London.
  • Gurnell, J. and Wauters, L. (1999) Callosciurus erythraeus. In The Atlas of European Mammals. Mitchell-Jones, A.J., Amori, G., Bogdanowicz, W., Krystufek, B., Reijnders, P.J.H., Spitzenberger. F., Stubbe, M., Thissen, J.B.M., Vohohralik, V. & Zima, J. (Eds.) pp. 182-183. Academic press, London.
  • Garvish, L. and Gurnell, J. (1999) Sciurus anomalus. In The Atlas of European Mammals. Mitchell-Jones, A.J., Amori, G., Bogdanowicz, W., Krystufek, B., Reijnders, P.J.H., Spitzenberger. F., Stubbe, M., Thissen, J.B.M., Vohohralik, V. & Zima, J. (Eds.) pp. 176-177. Academic press, London.
  • Massingham Hart, R. (1999) Squirrel Proofing your Home and Garden. Workman Publishing Company. ISBN: 1580171915
  • Mathias, M.L. & Gurnell, J. (1999) Status and conservation of the red squirrel (Sciurus vulgaris L) in Portugal. Hystrix 10: 13-19.
  • Osborn, D.A. (1999) Squirrel dog basics: a guide to hunting squirrels with dogs. Tree Top Publications, Watkinsville, Georgia, 151 pp.
  • Rushton, S.P., Lurz, P.W.W., South, A.B. & Mitchell-Jones, A. (1999). Modelling the distribution of red squirrels on the Isle of Wight. Animal Conservation, 2, 111-121
  • Verbeylen, G., De Bruyn, L. & Matthysen, E. (1999). Inventarisatie van de Aziatische grondeekhoorn in De Panne. Een project van de UA groep Dierenecologie in opdracht van AMINAL afdeling Natuur. Rapport 2 – Augustus-Oktober 1999.
  • Wauters, L.A. & Gurnell, J. (1999) The mechanism of replacement of red squirrels by grey squirrels: a test of the interference competition hypothesis. Ethology 105: 1053-1071.

Selected Pre-1999

  • Lurz, P.W.W., Garson, P.J. & Rushton, S.P., (1995). The ecology of squirrels in spruce dominated plantations: implications for management. Forest Ecology and Management, 79, 79-90.
  • Lurz, P.W.W., Garson, P.J., Wauters, L. (1997). Effect of temporal and spatial variation in habitat quality on red squirrel, Sciurus vulgaris, dispersal behaviour. Animal Behaviour 54, 427-435.
  • Lurz, P.W.W., Garson P.J. & Ogilvie J.F. (1998) Conifer species mixtures, cone crops and red squirrel conservation Forestry 71, 67-71.
  • Rushton, S.P., Lurz, P.W.W., Fuller, R. & Garson, P.J. (1997). Modelling the distribution of the red and grey squirrel at the landscape scale: a combined GIS and population dynamics approach. J. Appl. Ecol., 34, 1137-1154.
  • Rushton, S.P. , Lurz, P.W., Fuller, R. and Garson, P.J. (1997) Modelling the distribution of the red and grey squirrel at the landscape scale: a combined GIS and population dynamics approach. J. Appl. Ecol, 34, 1137-1154.
  • Verbeylen, G. & Matthysen, E. (1998). Inventarisatie van de Aziatische grondeekhoorn in De Panne. Een project van de UIA groep Dierenecologie in opdracht van AMINAL afdeling Natuur. Rapport September-November 1998.
  • Verbeylen, G. & Wauters, L. (1997). Habitatversnippering en eekhoorns : een vergelijking met vogelstudies. Limosa, 70, 38.
  • Villalba, S., Gulinck, H., Verbeylen, G. & Matthysen, E. (1998). Relationship between patch connectivity and the occurrence of the European red squirrel, Sciurus vulgaris, in forest fragments withi n heterogeneous landscapes. In : Dover, J.W. & Bunce, R.G.H. (eds.). Key Concepts in Landscape Ecology. IALE(UK), Preston, 205-220.

Bedtime listening

On Monday 4th August 2003, a radio programme was broadcast of BBC Radio 4 at 21.00 (British Summer Time) called, Can the red squirrel survive in Europe if the grey squirrel spreads over the Italian Alps?. To quote from the BBC website:

“Lionel Kelleway travels to Italy, to discover how the grey squirrel arrived there after World War Two and has now travelled north to the Italian Alps. In its wake it has devastated the native red squirrel population and is poised to disperse across Europe. With the help of continuous forest and few physical barriers, their spread is likely to be rapid. Lionel asks if there is hope for the red squirrel if the grey squirrel crosses Italy’s border and colonises the rest of mainland Europe.”

The programme features Piero Genovesi, Italo Currado, Sandro Bertolino and Luc Wauters. To listen to the programme again, go to the Radio 4 Wild Europe You will need a copy of “Real One Player” to listen to the broadcast, downloadable free from the link on the BBC page.

Forestry Commission Publications

Management of grey squirrels web

Information about FC publications in general can be found

Finnegan, L., Edwards, C. & Rochford, J. (2008) Origin of, and conservation units in, the Irish red squirrel ( Sciurus vulgaris ) population. Conservation Genetics 9: 1099-1109.