Red Squirrels Research Articles

A camera trap method for estimating target densities of grey squirrels to inform wildlife management applications

Effective wildlife population management requires an understanding of the abundance of the target species. In the United Kingdom, the increase in numbers and range of the non-native invasive grey squirrel Sciurus carolinensis poses a substantial threat to the existence of the native red squirrel S. vulgaris, to tree health, and to the forestry industry. Reducing the number of grey squirrels, is crucial to mitigate their impacts. Camera traps are increasingly used to estimate animal abundance, and methods have been developed that do not require the identification of individual animals. Most of these methods have been focussed on medium to large mammal species with large range sizes and may be unsuitable for measuring local abundances of smaller mammals that have variable detection rates and hard to measure movement behaviour. The aim of this study was to develop a practical and cost-effective method, based on a camera trap index, that could be used by practitioners to estimate target densities of grey squirrels in woodlands to provide guidance on the numbers of traps or contraceptive feeders required for local grey squirrel control. Camera traps were deployed in ten independent woods of between 6 and 28 ha in size. An index, calculated from the number of grey squirrel photographs recorded per camera per day had a strong linear relationship (R2 = 0.90) with the densities of squirrels removed in trap and dispatch operations. From different time filters tested, a 5 min filter was applied, where photographs of squirrels recorded on the same camera within 5 min of a previous photograph were not counted. There were no significant differences between the number of squirrel photographs per camera recorded by three different models of camera, increasing the method’s practical application. This study demonstrated that a camera index could be used to inform the number of feeders or traps required for grey squirrel management through culling or contraception. Results could be obtained within 6 days without requiring expensive equipment or a high level of technical input. This method can easily be adapted to other rodent or small mammal species, making it widely applicable to other wildlife management interventions.

Future Range Dynamics Suggest Increasing Threats of Grey Squirrels (Sciurus carolinensis) against Red Squirrels (Sciurus vulgaris) in Europe: A Perspective on Climatic Suitability

Interactions between the introduced gray squirrel (Sciurus carolinensis) and the native red squirrel (S. vulgaris) play an important role in the ecological equilibrium of European forest ecosystems. However, the range dynamics of the grey squirrel and red squirrel under future climate change scenarios remain unknown. The present study examined the range dynamics of grey squirrels and red squirrels in Europe and their range overlap now and in the future based on climate change. Under the most optimistic climate change scenario (SSP126), expansion of the grey squirrel’s range was mainly predicted in Germany, France, Croatia, Serbia, and Bulgaria. Under the most pessimistic climate change scenario (SSP585), expansion of the grey squirrel’s range was predicted in vast and scattered regions. Additionally, France, Italy, and Germany were overlapping ranges for the grey squirrel and red squirrel in the future under the SSP126 scenario but not under the current conditions, suggesting that there will be new regions where grey squirrels may threaten red squirrels in the future under SSP126. The range overlaps under the SSP585 scenario but not under the current conditions were vast and scattered, suggesting that there will be new regions in the future where grey squirrel may displace red squirrels under SSP585. Despite considerable variation, we detected expansions in the grey squirrel and red squirrel ranges and an increase in overlapping ranges between grey squirrels and red squirrels in the future. Therefore, our prediction suggests increasing threats of grey squirrels toward red squirrels in Europe in the future under climate change, which may impact the ecological equilibrium of European forest ecosystems.

From Postmigrant to Posthuman

A recent trend in Black German theatre engages with fantasy and posthumanism to criticize German racism and nationalism. In Krieg der Hörnchen (War of the Squirrels), Simone Dede Ayivi combines posthumanism and postnationalism, using German fears of invasive gray squirrels taking over the habitat of native red squirrels to reimagine xenophobic and racist debates about migration.

Nest box entrance hole size can influence nest site selection and nest defence behaviour in Japanese tits.

Birds have the ability to assess the risk of predation in their environment and adjust their antipredation strategies based on this risk information. However, whether nest site selection has effect on subsequent nest defence behaviour has not been studied. In this study, we aimed to determine whether the Japanese tit (Parus minor) exhibits a nest-box hole size preference and whether the entrance hole sizes of nest boxes influence the nest defence behaviour of tits. We hung nest boxes with three different entrance hole sizes (diameters: 6.5cm, 4.5cm and 2.8cm) in our study sites and investigated which nest boxes were occupied by tits. In addition, by using dummy-presentation experiments, we observed the nest defence behaviours of tits that nested in boxes with 2.8cm and 4.5cm entrance holes towards common chipmunks (Tamias sibiricus, a small nest predator able to enter these holes) and Eurasian red squirrels (Sciurus vulgaris, a large nest predator unable to enter the 2.8cm entrance hole). The tits that bred in nest boxes with 2.8cm entrance holes exhibited more intense nest defence responses to chipmunks than to squirrels. In contrast, the tits that bred in nest boxes with 4.5cm entrance holes exhibited similar nest defence responses to chipmunks and squirrels. Additionally, Japanese tits that bred in nest boxes with 2.8cm entrance holes exhibited more intense behavioural responses to chipmunks than those that bred in nest boxes with 4.5cm entrance holes. Our results suggested that Japanese tits prefer to occupy nest boxes with small holes for breeding and that nest-box characteristics influenced their nest defence behaviour.

The use of boreal relict shrub habitats of willow-leaf meadow sweet (Spiraea salicifolia) and shrubby cinquefoil (Potentilla fruticosa) in Western Rhodope Mts. by mammal species

Plant communities of two peat-shrub species – Spiraea salicifolia and Potentilla fruticosa were studied in the Rhodope Mts., with emphasis on their use as a resource for the mammals associated with them. These shrubs are boreal relicts among the dominant coniferous forests. The field surveys were conducted in the spring-autumn period of 2021–2022. In both study areas, the species composition of the mammals was studied by camera traps for medium and large mammals, and by Sherman live traps for small mammals. The species registered were roe deer (Capreolus capreolus), red fox (Vulpes vulpes), wild boar (Sus scrofa), pine marten (Martes martes), European hare (Lepus europaeus), red squirrel (Sciurus vulgaris), bank vole (Myodes glareolus) and yellow-necked mouse (Apodemus flavicollis). Having in mind that small mammals are vital prey base for avian and mammalian predators, it is not surprising that M. glareolus and A. flavicollis individuals were captured in the habitats that they probably use as shelters. The pine marten inhabits the forests by which the community of P. fruticosa is surrounded, but probably feeds on the rodents in the shrub. In this way, it probably provides it with an alternative to the forest food base and hunting ground. From the presented results, it seems that the L. europaeus uses P. fruticosa shrubs as food. Therefore, the plant communities of the two relict peat-shrub species studied probably provide shelter and food for the mammals. Their importance is established for at least one species of mammal with conservation significance at national and European level – M. martes. Therefore, it is necessary to continue and expand the future monitoring on mammal diversity of these relict communities.

A preliminary camera trapping study of mammals of Monti Lepini (Central Italy)

We used 52 camera traps to survey mammal species in the Lepini Mountains (Lazio, Central Italy) during three trapping sessions. Thirteen mammal species have been recorded. Compared to data based on previous opportunistic observations (2000-2018), camera trapping has quickly increased knowledge about the distribution of species, especially for elusive ones. We modelled species and average community occupancy also considering habitat covariates in a hierarchical modelling framework. Occupancy at community level was positively impacted by woods and negatively impacted by open habitats, indicating that the ongoing reforestation of the area may favour mammal diversity. Open surfaces have a negative effect on the presence of Sciurus vulgaris, a species for which our study confirms extensive recolonization of the area. We have also shown that woods increase the probability of occupation by Canis lupus and Felis silvestris, confirming that these species could be negatively impacted by increased deforestation.

Monitoring of squirrelpox in Scotland’s red squirrels (Sciurus vulgaris) – identification of a sentinel case in a naïve population?

Monitoring of squirrelpox in Scotland’s red squirrels (Sciurus vulgaris) – identification of a sentinel case in a naïve population?

Survey of Toxoplasma gondii in Urban and Rural Squirrels (Sciuridae) in Manitoba, Canada.

The coccidian parasite Toxoplasma gondii is found worldwide infecting warm-blooded vertebrates. Felids are the definitive hosts; other species act as intermediate hosts. Squirrels (Sciuridae) generally have high population densities in cities and forage and cache food on the ground, where they may come into contact with T. gondii oocysts or be preyed upon by cats and other carnivores. This environment might make squirrels important intermediate hosts of T. gondii in cities, and infection rates could indicate environmental levels of oocysts in soil. We investigated whether urban squirrels would be more exposed to T. gondii infection than rural squirrels with samples collected from American red squirrels (Tamiasciurus hudsonicus), eastern grey squirrels (Sciurus carolinensis), northern flying squirrels (Glaucomys sabrinus), and least chipmunks (Tamias minimus) in and around Winnipeg, Manitoba, Canada. We tested 230 tissue samples from 46 squirrels for T. gondii DNA by quantitative PCR and 13 serum samples from grey squirrels for T. gondii antibodies by competitive ELISA. We found no evidence of infection in any squirrel, indicating that squirrels are probably not important intermediate hosts of T. gondii in cities and that consumption of oocysts in the soil in general may not be an important contributor to transmission in colder environments.

The retrieval of food hoarded by red squirrels inhabiting an urban park

Food hoarding is a useful evolutionary adaptation which strongly affects animal fitness. However, its effectiveness depends on the trade-off between costs of gathering supplies and the benefits of using them by a hoarder when other food is hardly available. A field experiment conducted between November and April in a large urban park in Warsaw (Poland) showed that the survival rate of hazelnuts Corylus avellana hoarded by red squirrels Sciurus vulgaris was very low – about half of nuts disappeared from caches within one day, and after 50 days the probability of nut survival was 0.01. The survival rate of hazelnuts cached by squirrels was lower than these hidden in control caches. This difference suggests that squirrel-made caches were recovered by caching individuals and/or robbed by pilferers, both conspecific and heterospecific, more successfully than man-made caches. Moreover, survival rates of nuts deployed in control caches in clumps of trees were lower than in the open space areas avoided by squirrels. The probability of nut survival in a squirrel cache and in the control cache increased with the increasing proportion of days with frost as frozen soil limit squirrel access to cached nuts. The probability of nut survival in a squirrel cache and in control cache in the clumps of trees increased over the study period. We discuss whether food hoarding in the environmental conditions of an urban park where animals are oversupplied with food by humans is beneficial for squirrels or if it is an unimportant imprinted behaviour which does not increase their fitness.

A NEW SPECIES OF FLEA (SIPHONAPTERA: CTENOPHTHALMIDAE) PARASITIZING VOLES AT HIGH ELEVATIONS IN THE GREAT SMOKY MOUNTAINS OF TENNESSEE AND NORTH CAROLINA.

Both sexes of Catallagia appalachiensis n. sp. are described from high elevation spruce-fir forests in Sevier County, Tennessee and adjoining Swain County, North Carolina in the Great Smoky Mountains National Park. The type host of the new flea is the southern red-backed vole, Myodes gapperi (Vigors) (25 flea specimens), although small numbers of specimens were also collected from a sympatric northern short-tailed shrew, Blarina brevicauda (Say) (2 fleas), a red squirrel, Tamiasciurus hudsonicus (Erxleben) (1 flea), and a North American deer mouse, Peromyscus maniculatus (Wagner) (1 flea). Infestation prevalences for these hosts are provided. The new species is compared morphologically with other known species of Catallagia, in particular with Catallagia borealis, the only other described congeneric flea in eastern North America. This is the first new species of flea to be described from the eastern United States since 1980.

Model & Data Files for Analyses in "Differential impacts of spruce beetle outbreaks on snowshoe hares and red squirrels in the southern Rocky Mountains"

Model & Data Files for Analyses in "Differential impacts of spruce beetle outbreaks on snowshoe hares and red squirrels in the southern Rocky Mountains"

Red Squirrel Tests: Air Products' ammonia field experiments

AbstractThe Red Squirrel ammonia field experiments were conducted at the DNV Spadeadam site in the UK in 2022. Field test data currently exists for high‐pressure (ambient temperature) two‐phase releases of ammonia from Desert Tortoise (1983) and FLADIS (1996) experiments. No field tests have ever been done for cold (refrigerated) ammonia liquid spills on dry land or into water. The handling of liquified ammonia, during storage/processing and transportation, in a cold (refrigerated) state is inherently safer than in a high‐pressure (ambient temperature) liquified state. The main objective of the Air Products’ Red Squirrel Tests was to determine the source term and dispersion characteristics for high‐pressure (ambient temperature) liquified ammonia and low‐pressure (cold/refrigerated) liquified ammonia in form of two‐phase releases and liquid spills, respectively. Liquid spills on concrete and water were studied, along with the process conditions that led to the transition from liquid spills to two‐phase flow regimes based on discharge pressures for cold liquified ammonia. Details on the equipment, instrumentation, secondary containment, and ammonia sensors and their layout are presented. An initial analysis of the source terms and dispersion behavior for two‐phase releases and contained liquid spills over a range of weather conditions is also provided.

Opportunistic viral surveillance confirms the ongoing disease threat grey squirrels pose to sympatric red squirrel populations in the UK.

Red Squirrels United was a UK landscape-scale grey squirrel management programme undertaken between 2016 and 2020. A total of 11034 grey squirrels were removed by culling, with 1506 necropsied and 1405 suitable for adenovirus (AdV) or squirrelpox virus (SQPV) quantitative PCR (qPCR) analysis. Spleen, lip or hair were extracted, and DNA was isolated, with samples tested in duplicate by qPCR. Of 1378 tissue samples, 43% were positive for AdV and 10% for SQPV. Of 1031 hair samples, 11% were positive for AdV and 10% for SQPV. Overall, 762 of 1405 (54%) animals were positive for one or both viruses. Ad hoc sampling was undertaken from limited geographical areas but provided the only dataset from that period, instead of extrapolating from historical data. The grey squirrel is an asymptomatic reservoir host for AdV and SQPV. Interspecific infection transmission potential is demonstrated. Grey squirrel management by culling is essential for mainland red squirrel viability until other suitable management tools are available.

Craniodental divergence associated with bite force between hybridizing pine squirrels (Tamiasciurus).

Bite force can be a limiting factor in foraging and can significantly affect the competitive ability and lifetime fitness of mammals. Tamiasciurus squirrels feed primarily on conifer seeds and have a strong bite force to mechanically extract seeds from conifer cones with their mouths. In the North Cascades region, Douglas squirrels (Tamiasciurus douglasii) and red squirrels (T. hudsonicus) occupy ecologically different forests with different hardnesses in conifer cones. The ranges of these species overlap in a narrow hybrid zone where these forests meet near the crest of the North Cascades. We examined interspecific divergence in dietary ecomorphology in allopatry, in sympatry within the hybrid zone, and between hybrids and each parental species. We focused on three craniodental traits, including the incisor-strength index as a proxy measure for maximal bite force, cranial-suture complexity, and mandible shape. We find that these sister squirrel species differ in bite force and suture complexity in allopatry and sympatry and that mandible shape changes with the expected hardness of accessed food items, but is not significantly different between species. Furthermore, we find that hybrids display morphologies that overlap with hybrid zone red squirrels but not with hybrid zone Douglas squirrels. This work shows how important ecological processes at shallow evolutionary timescales can impact the divergence of morphological traits in taxa with extreme conservation of craniomandibular shape.

Interactions between native and invasive species: A systematic review of the red squirrel-gray squirrel paradigm

The eastern gray squirrel (Sciurus carolinensis) has been labeled as one of the 100 worst invasive alien species by the IUCN. In Europe, the species has been introduced to Britain, Ireland and Italy, and its subsequent spread has resulted in wide-scale extinction of native Eurasian red squirrels (Sciurus vulgaris) from the areas colonized by the gray squirrel. This replacement of a native by an alien competitor is one of the best documented cases of the devastating effects of biological invasions on native fauna. To understand how this replacement occurs, we present a systematic review of the literature on competition and interactions between red and gray squirrels. We describe the patterns of red and gray squirrel distribution in those parts of Europe where gray squirrels occur and summarize the evidence on the different processes and mechanisms determining the outcome of competition between the native and alien species including the influence of predators and pathogens. Some of the drivers behind the demise of the red squirrel have been intensively studied and documented in the past 30 years, but recent field studies and mathematical models revealed that the mechanisms underlying the red-gray paradigm are more complex than previously thought and affected by landscape-level processes. Therefore, we consider habitat type and multi-species interactions, including host-parasite and predator-prey relationships, to determine the outcome of the interaction between the two species and to better address gray squirrel control efforts.

Geographical variation in nest defense among cinereous tit populations in China.

Behavioral divergence among populations is common across taxonomic groups, still we know very little about anti-predator behaviors. Animal exposure to predation risk is variable in different ecological contexts. In addition, reproduction value of animals in different geographical regions usually varies. In this study, we tested whether cinereous tits Parus cinereus in different populations exhibited nest defense behaviors similar to those of nest or adult predators and whether their nest defense behaviors showed geographical variation. By using field dummy experiments, we observed tits' nest defense behavior in nest predator common chipmunk Tamias sibiricus and red squirrel Sciurus vulgaris, adult predator Eurasian sparrowhawk Accipiter nisus and nonthreatening species Oriental turtle dove Streptopelia orientalis in the ZJ (44° N), DZ (31° N), and DLS (18° N) populations, respectively. The response scores varied significantly across the 4 dummies in ZJ-tits and DLS-tits but did not in DZ-tits. When facing the chipmunk, ZJ-tits showed the highest response score and DZ-tits showed the lowest response score. When facing the squirrel, ZJ-tits showed a higher response score than tits in the other 2 populations. However, tits among the 3 populations responded similarly to a sparrowhawk or dove with slight response behaviors. In addition, response scores to nest predators were positively correlated with brood size across the 3 populations, but no trend was found for sparrowhawks or doves. Our results indicated that the nest defense behaviors of cinereous tits have evolved in response to large-scale geographical variation in ecological contexts and reproduction value.

Camera trapping efficiency in studying daily activity patterns of Turkestan lynx in the Northern Tien Shan

In order to determine the relationship between elusive carnivorans and other species, understand the mechanisms of their adaptation in the environment, as well as for regulation of strategies for rare carnivores’ conservation, it is relevant and necessary to study their daily activity rhythms. As a nocturnal species in the remote mountains of the Northern Tien Shan, the behavioral ecology and, in particular, the activity rhythms of the Turkestan lynx (Lynx lynx isabellina Blyth, 1847) are poorly studied. This article presents data on the daily activity of the lynx and an analysis of its correlation with the activity rhythms of its prey species in the Northern Tien Shan using camera traps. As a result of research conducted in Ile and Kungei Alatau from 2013 to 2022, we used 11,258 trap-days and obtained 59 frames with individual passages of Turkestan lynx and 528 frames with passages of its prey species – tolai hare (Lepus tolai), Siberian roe deer (Capreolus pygargus), Siberian ibex (Capra sibirica), wild boar (Sus scrofa), red tree squirrel (Sciurus vulgaris exalbidus) and red deer (Cervus elaphus). The rhythms of lynx’s daily activity coincided with the activity of its prey in three different time peaks: in the early morning, in the afternoon, and at night. Tolai hare in Kungei Alatau and Siberian roe deer in Ile Alatau play a significant role in the conservation of the lynx population. The results obtained prove the need to protect these six species to ensure the Turkestan lynx populations stability in the Northern Tien Shan. Keywords: Turkestan lynx, daily activity, specially protected natural areas, camera traps

High δ 13C values in red squirrels Sciurus vulgaris explained by a reliance on conifer seeds

ABSTRACT Eurasian red squirrels Sciurus vulgaris have unusually high δ 13C values compared to other forest rodents, which is seemingly related to the consumption of 13C-enriched conifer seeds. To test this hypothesis, we analyzed the hair of wild and zoo-kept red squirrels, seeds of pine and spruce, and feathers of specialized and opportunistic consumers of conifer seeds, crossbills Loxia spp., and woodpeckers Dendrocopos major. Data on the isotopic composition (δ 13C and δ 15N values) of hair or feathers of other species of forest rodents and birds were obtained from published studies. The range of mean δ 13C values of hair of wild forest rodents (19 species) exceeded 10 ‰. All squirrel species had high 13C content, S. vulgaris having maximum δ 13C values. In contrast, S. vulgaris kept in captivity had an isotopic composition similar to other captive rodents. The feathers of crossbills were enriched in 13C compared to other forest birds (15 species), while seeds of coniferous trees often had higher δ 13C values compared to seeds of other woody plants. Distinctiveness of the isotopic composition of mammals and birds feeding on the seeds of coniferous trees suggests that this resource can be traced through the entire forest food web.

Beaver activity and red squirrel presence predict bird assemblages in boreal Canada

AbstractWetlands and predation in boreal ecosystems play essential roles throughout the breeding season for bird assemblages. We found a positive association of beaver activity and a negative influence of American red squirrels (Tamiasciurus hudsonicus) on bird assemblages. We used a multispecies hierarchical model to investigate whether bird communities differ between two major wetland habitats in boreal Canada: beaver ponds and peatland ponds. In addition to including variables such as forest cover and latitude, we adopted a structural equation model approach to estimate the occupancy of American red squirrels and its potential influence on bird communities. Using automated recording stations deployed at 50 ponds, we detected 96 bird species in 2018 and 2019. Bird species were grouped into four taxonomic guilds according to their habitat successional requirements: early successional species, late successional species, generalists, and wetland species. Beaver ponds harbored higher species richness, a pattern driven primarily by early successional species. The occupancy of almost a quarter of the species was lower in the presence of red squirrels. Late successional species responded positively to the cover of forest surrounding the pond. Our results highlight the value of considering acoustic data of red squirrels to quantify habitat quality in boreal forests. We conclude that beaver activity shapes bird assemblages through modification of their habitat, and that some bird guilds are associated negatively with the presence of American red squirrels.

Using a substitute species to inform translocation of an endangered territorial mammal.

Substitute species can inform management strategies without exposing endangered species to unacceptable risk. Furthermore, experimental approaches may help to identify the causes of translocation failures, improving the chances of success. We used a surrogate subspecies, Tamiasciurus fremonti fremonti to test different translocation techniques to inform on potential management actions with regards to the endangered Mt. Graham red squirrel (Tamiasciurus fremonti grahamensis). Individuals of both subspecies defend year-round territories in similar mixed conifer forests at elevations between 2650-2750 m, where they store cones to survive over winter. We fitted VHF radio collars to 54 animals, and we monitored their survival and movements until individuals settled on a new territory. We considered the effect of season, translocation technique (soft or hard release), and body mass on survival, distance moved after release, and time to settlement of translocated animals. Survival probability averaged 0.48 after 60 days from the translocation event and was not affected by season or translocation technique. 54% of the mortality was caused by predation. Distance moved and number of days to settlement varied with season, where winter was characterized by shorter distances (average of 364 m in winter versus 1752 m in fall) and a smaller number of days (6 in winter versus 23 in fall). The data emphasized on the potential of substitute species to provide valuable information for possible outcomes of management strategies to closely related endangered species.