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.


  • 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. doi:

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.

  • 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: n 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.

  • 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.

  • 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. (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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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

  • 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.

  • 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.   doi:

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  doi:

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.

  • 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.

  • 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. doi:

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 < 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.
  • Chantrey, J., Dale, T. D., Read, J. M., White, S., Whitfield, F., Jones, D., et al. (2014) European red squirrel population dynamics driven by squirrelpox at a gray squirrel invasion interface. Ecology and Evolution 4: 3788-3799.
  • Cudworth, N. & Koprowski, J. (2014) Survival and mortality of the Arizona gray squirrel (Sciurus arizonensis). The Southwestern Naturalist 59: 423-426.
    Bateman, P.W. & Fleming, P.A. (2014) Does human pedestrian behaviour influence risk assessment in a successful mammal urban adapter? Journal of Zoology 294:93-98.
  • Bertolino, S., Montezemolo, N., Preatoni, D., Wauters, L. & Martinoli, A.  (2014) A grey future for Europe: Sciurus carolinensis is replacing native red squirrels in Italy. Biological Invasions 16: 53-62.
  • Bonnington, C., Gaston, K. & Evans, K. (2014) Squirrels in suburbia: influence of urbanisation on the occurrence and distribution of a common exotic mammal. Urban Ecosystems 17: 533-546.
  • Bonnington, C., Gaston, K., &  Evans,K.L. (2014) Relative roles of grey squirrels, supplementary feeding, and habitat in shaping urban bird assemblages. PLoS ONE 9: e109397.
  • Boutin, S. & Lane, J.E. (2014) Climate change and mammals: evolutionary versus plastic responses. Evolutionary Applications 7: 29-41.
  • Chavez, A. S., & Kenagy, G. J. (2014) Clinal colour variation within a panmictic population of tree squirrels, I (Rodentia: Sciuridae), across an ecological gradient. Biological Journal of the Linnean Society n/a-n/a.
  • Collins, L.M., Warnock, N.D., Tosh, D.G., McInnes, C., Everest, D., Montgomery, W.I., Scantlebury, M., Marks, N., Dick, J.T.A. & Reid, N. (2014)  Squirrelpox virus: assessing prevalence, transmission and environmental degradation. PLoS ONE 9: e89521.
  • Darby, A.C., McInnes, C.J., Kjaer, K.H., Wood, A.R., Hughes, M., Martensen, P.M., Radford, A.D., Hall, N. & Chantrey, J. (2014) Novel host-related virulence factors are encoded by squirrelpox virus, the main causative agent of epidemic disease in red squirrels in the UK. . PLoS One 9: e96439.
  • Everest, D. J., Shuttleworth, C. M., Stidworthy, M. F., Grierson, S. S., Duff, J. P., & Kenward, R. E. (2014) Adenovirus: an emerging factor in red squirrel Sciurus vulgaris conservation. Mammal Review, n/a-n/a.
  • Flaherty, S., Lurz, P.W.W. & Patenaude, G. (2014) Use of LiDAR in the conservation management of the endangered red squirrel (Sciurus vulgaris L.). Journal of Applied Remote Sensing 8: 083592-083592.
  • Fletcher, Q.E., Speakman, J.R., Boutin, S., Lane, J.E., McAdam, A.G., Gorrell, J.C., Coltman, D.W. & Humphries, M.M. (2014) Daily energy expenditure during lactation is strongly selected in a free-living mammal. Functional Ecology 29: 1985-208.
  • Gurnell, J., Lurz, P. W. W., & BertoldiI, W. (2014) The changing patterns in the distribution of red and grey squirrels in the North of England and Scotland between 1991 and 2010 based on volunteer surveys. Hystrix, the Italian Journal of Mammalogy 25:
  • Hatten, J.R. (2014) Mapping and monitoring Mount Graham red squirrel habitat with Lidar and Landsat imagery. Ecological Modelling 289: 106-123.
  • Liu, Z., Li, B., Ma, J., Zheng, D., & Xu, Y. (2014) Phylogeography and genetic diversity of the red squirrel (Sciurus vulgaris) in China: Implications for the species’ postglacial expansion history. Mammalian Biology – Zeitschrift für Säugetierkunde 79: 247-253.
  • Luo, Y., Yang, Z., Steele, M. A., Zhang, Z., Stratford, J. A., & Zhang, H. (2014) Hoarding without reward: rodent responses to repeated episodes of complete cache loss. Behavioural Processes 106: 36-43.
  • Lurz, P. (2014) Changing ‘Red to Grey': Alien Species Introductions to Britain and the Displacement and Loss of Native Wildlife from our Landscapes. In Displaced Heritage. pp. 265-272. Boydell & Brewer.
  • Martínez-Duque, P., Avila-Flores, R., Emerson, G. L., Carroll, D. S., Suzán, G., & Gallardo-Romero, N. F. (2014) Orthopoxvirus Antibodies in Grey Squirrels (Sciurus aureogaster) in Mexico City, Mexico. Journal of Wildlife Diseases 50, 696-698.
  • McGowan, N.E., Marks, N.J., McInnes, C.J., Deane, D., Maule, A.G. & Scantlebury, M. (2014) Effects of parasitism and morphology on squirrelpox virus seroprevalence in grey squirrels (Sciurus carolinensis). PLoS ONE 9: e83106.
  • Murrant, M. N., Bowman, J., & Wilson, P. J. (2014) A test of non-kin social foraging in the southern flying squirrel (Glaucomys volans). Biological Journal of the Linnean Society n/a-n/a.
  • Palmer Rosa, R. & Koprowski John, L. (2014) Feeding behavior and activity patterns of Amazon red squirrels. Mammalia 78: 303.
  • Palmer, G.H., Koprowski, J.L. & Pernas, AJ. (2014) Distribution and spread of an introduced insular population of red-bellied squirrels (Sciurus aureogaster) in Florida.  Mammalia 78: 67-73.
  • Patterson, J. E. H., Neuhaus, P., Kutz, S. J., & Ruckstuhl, K. E. (2013) Parasite removal improves reproductive success of female North American red squirrels (Tamiasciurus hudsonicus). PLoS ONE 8: e55779.
  • Pisanu, B., Chapuis, J.-L., Dozières, A., Basset, F., Poux, V. & Vourc’h, G. (2014) High prevalence of Borrelia burgdorferis. L in the European red squirrel Sciurus vulgaris in France. Ticks and Tick-borne Diseases 5: 1-6.
  • Ramos-Lara, N., & Koprowski, J. L. (2014) Spacing behavior of a non-larder-hoarding Tamiasciurus: a study of Mearns’s squirrels in xeric coniferous forests. Ethology 121: 196-205.
  • Ramos-Lara, N., & Koprowski, J. (2014) Deforestation and knowledge gaps threaten conservation of less charismatic species: status of the arboreal squirrels of Mexico. Mammalia 78: 417-427.
  • Rézouki, C., Dozières, A., Le Cœur, C., Thibault, S., Pisanu, B., Chapuis, J.-L., et al. (2014) A viable population of the European red squirrel in an urban park. PLoS ONE 9: e105111.
  • Rocha, R., Wauters, L., Mathias, M. L., & Fonseca, C. (2014) Will an ancient refuge become a modern one? A critical review on the conservation and research priorities for the red squirrel (Sciurus vulgaris) in the Iberian Peninsula.  Hystrix, Italian Journal of Mammalogy n/a-n/a..
  • Romeo, C., Ferrari, N., Rossi, C., Everest, D.J., Grierson, S.S., Lanfranchi, P., Martinoli, A., Saino, N., Wauters, L.A. & Hauffe, H.C. (2014) Ljungan Virus and an Adenovirus in Italian Squirrel Populations. Journal of Wildlife Diseases 50: 409-411.
  • Romeo, C., Wauters, L., Ferrari, N., Lanfranchi, P., Martinoli, A., Pisanu, B., Preatoni, D. & Saino, N. (2014)  Macroparasite Fauna of Alien Grey Squirrels (Sciurus carolinensis): Composition, Variability and Implications for Native Species. PLoS ONE 9, e88002.
  • Romeo, C., Ferrari, N., Rossi, C., Everest, D., Grierson, S., Lanfranchi, P., Martinoli, A., Saino, N., Wauters, L. &  Hauffe, H. (2014) Ljungan Virus and an Adenovirus in Italian Squirrel Populations. Journal of Wildlife Diseases 50: 409-411.
  • Schuchert, P., Shuttleworth, C., McInnes, C., Everest, D., & Rushton, S. (2014) Landscape scale impacts of culling upon a European grey squirrel population: can trapping reduce population size and decrease the threat of squirrelpox virus infection for the native red squirrel? Biological Invasions n/a-n/a.
  • Selonen, V., Hanski, I., & Wistbacka, R. (2014) Communal nesting is explained by subsequent mating rather than kinship or thermoregulation in the Siberian flying squirrel. Behavioral Ecology and Sociobiology 68: 971-980.
  • Shearer, L., Bray, R., & Toner, C. (2014) An experimental study investigating the ability of volunteers to identify squirrel species from tail–hair samples. Animal Biodiversity and Conservation 37: 145-147.
  • Shuttleworth, C., Everest, D., McInnes, C., Greenwood, A., Jackson, N., & Rushton, S., et al. (2014) Inter-specific viral infections: Can the management of captive red squirrel collections help inform scientific research? Hystrix, Italian Journal of Mammalogy 25: 18-24.
  • Sheehy, E. & Lawton, C. (2014) Population crash in an invasive species following the recovery of a native predator: the case of the American grey squirrel and the European pine marten in Ireland. Biodiversity and Conservation n/a-n/a.
  • Signorile, A., Paoloni, D. & Reuman, D. (2014)  Grey squirrels in central Italy: a new threat for endemic red squirrel subspecies. Biological Invasions n/a-n/a
  • Signorile, A.L., Wang, J., Lurz, P.W.W., Bertolino, S., Carbone, C. & Reuman, D.C.  (2014) Do founder size, genetic diversity and structure influence rates of expansion of North American grey squirrels in Europe? Diversity and Distributions n/a-n/a.
  • Stevenson-Holt, C. D., Watts, K., Bellamy, C. C., Nevin, O. T., & Ramsey, A. D. (2014) Defining Landscape Resistance Values in Least-Cost Connectivity Models for the Invasive Grey Squirrel: A Comparison of Approaches Using Expert-Opinion and Habitat Suitability Modelling. PLoS ONE 9: e112119.
  • Studd, E. K., Boutin, S., McAdam, A. G., Krebs, C. J., & Humphries, M. M. (2014) Predators, energetics and fitness drive neonatal reproductive failure in red squirrels. Journal of Animal Ecology n/a-n/a.
  • Vasilieva, N. A., & Tchabovsky, A. V. (2014) Timing is the only thing: reproduction in female yellow ground squirrels (Spermophilus fulvus). Canadian Journal of Zoology 92: 737-747.
  • White, A., Bell, S.S., Lurz, P.W.W. & Boots, M. (2014) Conservation management within strongholds in the face of disease-mediated invasions: red and grey squirrels as a case study. Journal of Applied Ecology n/a-n/a.
  • Williams, C. T., Barnes, B. M., Kenagy, G. J., & Buck, C. L. (2014) Phenology of hibernation and reproduction in ground squirrels: integration of environmental cues with endogenous programming. Journal of Zoology 292: 112-124.
  • Zong, C., Mei, S., Santicchia, F., Wauters, L., Preatoni, D., & Martinoli, A. (2014) Habitat effects on hoarding plasticity in the Eurasian red squirrel (Sciurus vulgaris). Hystrix, Italian Journal of Mammalogy 25: 14-17.


  • Benitez, V.V., Almada Chavez, S., Gozzi, A.C., Messetta, M.L. &  Guichón, M.L (2013) Invasion status of Asiatic red-bellied squirrels in Argentina. Mammalian Biology – Zeitschrift für Säugetierkunde 78: 164-170.
  • Bertolino, S., & Lurz, P. W. W. (2013) Callosciurus squirrels: worldwide introductions, ecological impacts and recommendations to prevent the establishment of new invasive populations. Mammal Review 43: 22-33.
  • Bonnington, C., Gaston, K.J. &  Evans, K.L. (2013) Assessing the potential for Grey Squirrels Sciurus carolinensis to compete with birds at supplementary feeding stations. Ibis 156: 220-226.
  • Bonnington, C., Gaston, K.J., & Evans, K.L. (2013) Fearing the feline: domestic cats reduce avian fecundity through trait-mediated indirect effects that increase nest predation by other species. Journal of Applied Ecology 50: 15-24.
  • Bonnington, C., Gaston, K. & Evans, K., (2013) Squirrels in suburbia: influence of urbanisation on the occurrence and distribution of a common exotic mammal. Urban Ecosystems 1-14.
  • Bosch, S. &  Lurz, PW..W. (2013) The process of drey construction in red squirrels – nestbox observations based on a hidden camera. Hystrix 24: 199-202.
  • Bosson, C., Palme, R., & Boonstra, R. (2013) Assessing the impact of live-capture, confinement, and translocation on stress and fate in eastern gray squirrels. Journal of Mammalogy 94: 1401-1411.
  • Brunner, J. L., Duerr, S., Keesing, F., Killilea, M., Vuong, H., & Ostfeld, R. S. (2013) An experimental test of competition among mice, chipmunks, and squirrels in deciduous forest fragments. PLoS ONE 8: e66798.
  • Chavez, A.S., Maher, S.P., Arbogast, B.S. & Kenagy, G.J. (2013) Diversification and gene flow in nascent lineages of island and mainland north american tree squirrels (Tamiasciurus). Evolution n/a-n/a.
  • Della-Flora, F., Melo, G., Sponchiado, J., & Cáceres, N. (2013) Association of the southern Amazon red squirrel Urosciurus spadiceus Olfers, 1818 with mixed species bird flocks. Mammalia 77 113-117.
  • Desantis, L.M., Delehanty, B., Weir, J.T., & Boonstra, R. (2013) Mediating free glucocorticoid levels in the blood of vertebrates: are corticosteroid-binding proteins always necessary? Functional Ecology 27: 107-119.
  • Di Febbraro, M., Lurz, P., Genovesi, P., Maiorano, L., Girardello, M., & Bertolino, S. (2013) The use of climatic niches in screening procedures for introduced species to evaluate risk of spread: a case with the american eastern grey squirrel. PLoS ONE 87.
  • Everest, D. J., Butler, H., Blackett, T., Simpson, V. R., & Shuttleworth, C. M. (2013) Adenovirus infection in red squirrels in areas free from grey squirrels. Veterinary Record 173: 199-200.
  • Fletcher, Q.E., Selman, C., Boutin, S., McAdam, A.G., Woods, S.B., Seo, A.Y., Leeuwenburgh, C., Speakman, J.R., & Humphries, M.M. (2013)  Oxidative damage increases with reproductive energy expenditure and is reduced by food-supplementation. Evolution 67: 1527-1536.
  • Getschow, C.M., Rivers, P., Sterman, S., Lumpkin, D.C. & Tarvin, K.A. (2013) Does gray squirrel (Sciurus carolinensis) response to heterospecific alarm calls depend on familiarity or acoustic similarity? Ethology: n/a-n/a.
  • Gür, H. (2013) The effects of the Late Quaternary glacial–interglacial cycles on Anatolian ground squirrels: range expansion during the glacial periods? Biological Journal of the Linnean Society 109: 19-32.
  • Lin, Z. (2013) Health surveillance and MHC Class II DRB genetic diversity in the red squirrel (Sciurus vulgaris) population of the Isle of Arran. Master of Veterinary Science, University of Edinburgh.
  • Mantooth, S. J., Hafner, D. J., Bryson, R. W., & Riddle, B. R. (2013) Phylogeographic diversification of antelope squirrels (Ammospermophilus) across North American deserts. Biological Journal of the Linnean Society n/a-n/a.
  • Mayle, B.A. & Broome, A.C. (2013) Changes in the impact and control of an invasive alien: the grey squirrel (Sciurus carolinensis) in Great Britain, as determined from regional surveys. Pest Management Science 69: 323-333.
  • McInnes, C. J., Coulter, L., Dagleish, M. P., Deane, D., Gilray, J., Percival, A., et al. (2013) The emergence of squirrelpox in Ireland. Animal Conservation 16: 51-59.
  • Monclús, R., von Holst, D., Blumstein, D. T., & Rödel, H. G. (2013) Long-term effects of litter sex ratio on female reproduction in two iteroparous mammals. Functional Ecology n/a-n/a.
  • Palmer, G., Koprowski, J., & Pernas, A. (2013) Nest tree and site selection of an introduced population of red-bellied squirrels (Sciurus aureogaster). Journal of Mammalogy 94: 1274-1281.
  • Ramos-Lara, N., Koprowski, J., & Swann, D. (2013) Nest-site characteristics of the montane endemic Mearns’s squirrel (Tamiasciurus mearnsi): an obligate cavity-nester? Journal of Mammalogy 94: 50-58.
  • Říčanová, Š., Koshev, Y., Říčan, O., Ćosić, N., Ćirović, D., Sedláček, F., et al. (2013) Multilocus phylogeography of the European ground squirrel: cryptic interglacial refugia of continental climate in Europe. Molecular Ecology 22: 4256-4269.
  • Romeo, C., Pisanu, B., Ferrari, N., Basset, F., Tillon, L., Wauters, L.A., Martinoli, A., Saino, N. & Chapuis, J.L. (2013) Macroparasite community of the Eurasian red squirrel (Sciurus vulgaris): poor species richness and diversity. Parasitol Res 112, 3527-3536.
  • Rong, K., Yang, H., Ma, J., Zong, C., & Cai, T. (2013) Food availability and animal space use both determine cache density of Eurasian red squirrels. PLoS ONE 8: e80632.
  • Selonen, V., Painter, J., Rantala, S. & Hanski, I. (2013) Mating system and reproductive success in the Siberian flying squirrel. Journal of Mammalogy 94: 1266-1273.
  • Signorile, A. (2013) Genetic determinants of the expansion of eastern grey squirrel populations across Europe. PhD, Imperial College London.
  • Simpson, S., Bleamoied, N., Peniche, G., Dozières, A., Blackett, T., Coleman, S., Cornish, N., & Groombridge, J. (2013) Genetic structure of introduced populations: 120-year-old DNA footprint of historic introduction in an insular small mammal population. Ecology and Evolution 3: 614-628.
  • Simpson, V., Hargreaves, J., Butler, H., Davison, N. & Everest, D. (2013) Causes of mortality and pathological lesions observed post-mortem in red squirrels (Sciurus vulgaris) in Great Britain. BMC Veterinary Research 9: 229.
  • Stevenson, C.D., Ferryman, M., Nevin, O.T., Ramsey, A.D., Bailey, S. & Watts, K. (2013) Using GPS telemetry to validate least-cost modeling of gray squirrel (Sciurus carolinensis) movement within a fragmented landscape. Ecology and Evolution n/a-n/a.
  • Xiao, Z., Gao, X. & Zhang, Z. (2013) Sensitivity to seed germination schedule by scatter-hoarding Pére David’s rock squirrels during mast and non-mast years. Ethology 119: 472-479.
  • Yi, X., Liu, G., Steele, M. A., Shen, Z., & Liu, C. (2013) Directed seed dispersal by a scatter-hoarding rodent: the effects of soil water content. Animal Behaviour 86: 851-857.
  • Zapponi, L., Del Bianco, M., Luiselli, L., Catorci, A. & Bologna, M.A. (2013) Assessing environmental requirements effects on forest fragmentation sensitivity in two arboreal rodents. Mammalian Biology – Zeitschrift für Säugetierkunde 78: 157-163.


  • Bosch, S. &  Lurz, P.W.W.  (2012) The Eurasian Red SquirrelSciurus vulgaris. Die Neue Brehm-Bücherei, English Edition Vol. 183, Hohenlohe, Germany. ISBN 978-3-89432-258-8.
  • Bosson, C.O., Islam, Z. & Boonstra, R. (2012) The impact of live trapping and trap model on the stress profiles of North American red squirrels. Journal of Zoology 288: 159-169.
  • Di Cerbo, A. and C. Biancardi (2012) Monitoring small and arboreal mammals by camera traps: effectiveness and applications. Acta theriologica: 1-5.
  • Digweed, S., Rendall, D., & Imbeau, T. (2012) Who’s your neighbor? Acoustic cues to individual identity in red squirrel Tamiasciurus hudsonicus rattle calls. Current Zoology 58: 758-764.
  • Dozières, A., Chapuis, J.-L., Thibault, S., & Baudry, E. (2012). Genetic structure of the French red squirrel populations: implication for conservation. PLoS ONE 7:  e47607.
  • Everest, D. J., Shuttleworth, C. M., Grierson, S. S., Duff, J. P., Jackson, N., Litherland, P., Kenward, R.E. & Stidworthy, M.F. (2012). Systematic assessment of the impact of adenovirus infection on a captive reintroduction project for red squirrels (Sciurus vulgaris). Veterinary Record 171:  176.
  • Flaherty, S., Patenaude, G., Close, A., & Lurz, P.W.W. (2012) The impact of forest stand structure on red squirrel habitat use.Forestry 85: 437-444.
  • Fletcher, Q.E., Speakman, J.R., Boutin, S., McAdam, A.G., Woods, S.B., & Humphries, M.M. (2012) Seasonal stage differences overwhelm environmental and individual factors as determinants of energy expenditure in free-ranging red squirrels. Functional Ecology 26: 677-687.
  • Gurnell, J. & Lurz, P.W.W. (2012) Red Squirrel, In:  Cresswell, W., Birks, J., Dean, M.D., Pacheco, M., Trewhella, W., Wells, D., Wray, S. (Eds.) UK BAP Mammals; Interim Guidance for Survey Methodologies, Impact Assessment and Mitigation. The Mammal Society, Southampton, pp. 9-21.
  • Gurnell, J., Lurz, P.W.W. & Wauters, L.A.  (2012) Squirrels. TheMammal Society,  Southampton, UK.  Pp. 35.
  • Mayle B, Ferryman M, Peace A, Yoder C, Miller L, & Cowan D. (2012) The use of DiazaCon™ to limit fertility by reducing serum cholesterol in female grey squirrel, Sciurus carolinensis. Pest management Science (2012).
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  • 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.
  • Bryce,J; Johnson,PJ; Macdonald,DM (2002) Can niche use in red and grey squirrels offer clues for their apparent coexistence?Journal of Applied Ecology 39, 875-887.
  • 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
  • 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.


    • 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.