Grey Squirrel Sciurus Carolinensis Research Articles

An assessment of seasonal bait uptake by individual grey squirrels to develop a delivery system for oral contraceptives.

Globally, human-wildlife conflicts continue to increase, owing to human population growth and expansion. Many of these conflicts concern the impacts of invasive non-native species. In the UK, the invasive, non-native grey squirrel Sciurus carolinensis negatively affects tree health and has caused the decline of the native red squirrel Sciurus vulgaris. Oral contraceptives are being developed to manage the impacts of the grey squirrel. To be effective, contraceptives will need to be deployed at a landscape scale, and will require a delivery system that is practical and economically viable. Understanding grey squirrel feeding behaviour is important so that delivery methods can be designed so that a sufficient number oftarget individuals receive an effective contraceptive dose at a time of year that will ensure their infertility throughout peak times of breeding. The main aims of this study were to assess how sex, season, squirrel density and bait point density influenced; (1) the probability of a squirrel visiting a feeder and (2) the amount of bait consumed from feeders. Field trials were conducted on six woodland populations of squirrels in three seasons, with four days of bait deployment via purpose-designed squirrel-specific bait hoppers with integrated PIT-tag readers. It was possible to deliver multiple doses on most days to most male and female grey squirrels, with bait deployment more likely to be effective in spring, immediately before the second annual peak in squirrel breeding, followed by winter, immediately before the first peak in breeding. The results from this study could be used to design methods for delivering oral contraceptive baits to grey squirrels in the future and the methods used could be applied to other small mammal species and other bait delivery systems. © 2024 Crown copyright and The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. This article is published with the permission of the Controller of HMSO and the King's Printer for Scotland.

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.

Into the drink: observation of a novel hunting technique employed by an Eastern Gray Squirrel (Sciurus carolinensis)

Observations of typically herbivorous species have shown that animals will opportunistically eat animal tissue that is either scavenged or hunted. Squirrels from a number of genera have been observed to hunt prey and consume meat in terrestrial ecosystems. Here we provide evidence of a novel hunting strategy employed by an Eastern Gray Squirrel (Sciurus carolinensis), which has not previously been observed hunting aquatic prey. More rigorous observational studies are needed to determine the extent of this behaviour in Eastern Gray Squirrel populations and whether fishing is a common foraging behaviour for this species.

Reproductive Traits of an Invasive Alien Population of Grey Squirrel (Sciurus carolinensis) in Central Italy.

The reproductive cycle of an invasive alien Italian grey squirrel population was studied to understand its adaptation and limit its spread, in order to conserve the autochthonous red squirrel. Female and male genital traits were evaluated throughout the reproductive cycle, including the ovary, uterus, testicle, epididymis, seminiferous tubule morphometry, and germinative epithelium histology. Moreover, individual female fecundity was determined by counting uterine scars. Ovary width and uterus weight, length, and width reached their highest values in the luteal and pregnancy phases. On conducting a histological evaluation of the testicular germinal epithelium, four morphotypes related to the different reproductive phases of the male squirrels were identified: immature, pubertal, spermatogenesis, and regressive. Testicle and epididymis weights and seminiferous tubule diameters reached their largest values during spermatogenesis. Uterine scar analysis showed that 69% of the females had given birth to one or two litters, while 31% had no uterine scars. Litters were larger in the first breeding period than in the second; annual fecundity was 4.52 ± 1.88 uterine scars/female. Umbrian grey squirrels have adapted to their non-native range, showing two annual mating periods at times similar to those in their native range, and high reproductive success.

Spillover of an alien parasite reduces expression of costly behaviour in native host species.

Understanding the effects of invasive alien species (IAS) on native host-parasite relationships is of importance for enhancing ecological theory and IAS management. When IAS and their parasite(s) invade a guild, the effects of interspecific resource competition and/or parasite-mediated competition can alter existing native host-parasite relationships and the dependent biological traits such as native species' behaviour. We used a natural experiment of populations of native red squirrels Sciurus vulgaris that were colonized by the alien grey squirrel Sciurus carolinensis, comparing repeated measurements of red squirrel parasite infection and personality with those taken in sites where only the native species occurred. We explored two alternative hypotheses: (a) individual differences in personality traits (activity and/or sociability) of native red squirrel positively affect the probability of macroparasite spillover and thus the likelihood to acquire the alien's parasitic helminth Strongyloides robustus; (b) the combined effects of grey squirrel presence and parasite infection result in a reduction of costly personality traits (activity and/or exploration). Using data from 323 arena tests across three experimental (native species and IAS) and three control sites (only native species), we found negative correlations between native species' activity and infection with S. robustus in the sites invaded by the alien species. Activity was also negatively correlated with infection by its native helminth Trypanoxyuris sciuri but only when grey squirrels were present, while in the red-only sites there was no relationship of T. sciuri infection with any of the personality traits. Moreover, individuals that acquired S. robustus during the study reduced their activity after infection, while this was not the case for animals that remained uninfected. Our results show that parasite-mediated competition is costly, reducing activity in individuals of the native species, and altering the native host-native parasite relationships.

Translocated native pine martens Martes martes alter short‐term space use by invasive non‐native grey squirrels Sciurus carolinensis

Abstract Predators can shape the distributions and dynamics of their prey through direct and indirect mechanisms. Where prey animals are regarded as pests, the augmentation of predator populations might offer a potential tool in their management. Declines in invasive non‐native grey squirrel Sciurus carolinensis populations in Ireland and Scotland have been related to an increase in range and density of native pine marten Martes martes populations. These reductions in grey squirrel abundance have, in turn, been linked to recovery of native red squirrels Sciurus vulgaris. Taking the opportunity presented by a conservation translocation of pine martens from Scotland to Wales, we investigated the short‐term effects of exposure to translocated martens on the space use and survival of resident grey squirrels. Grey squirrel range size and daily distance travelled increased significantly with increasing exposure to martens but we found no effect of marten exposure on the recapture probability (i.e. apparent survival) of the sampled squirrels within the study time frame. This is suggestive of contemporary, non‐lethal effects changing the ranging or foraging regimes of squirrels, due either to predator avoidance and/or earlier lethal effects associated with a reduction in intraspecific competition. Synthesis and applications. Our evaluation mimics the conditions experienced by grey squirrels at the front edge of naturally recovering pine marten populations and presents direct evidence that pine marten translocations could play an influential role in the behaviour and dynamics of invasive non‐native grey squirrel populations. Translocations of native predators, undertaken primarily for biodiversity conservation, could therefore find additional application in managing the ecological and economic impacts of invasive non‐native prey.

Learning is negatively associated with strength of left/right paw preference in wild grey squirrels (Sciurus carolinensis)

Cerebral laterality, via hemispheric specialisation, has been evidenced across the animal kingdom and linked to cognitive performance in a number of species. Previously it has been suggested that cognitive processing is more efficient in brains with stronger hemispheric differences in processing, which may be the key fitness benefit driving the evolution of laterality. However, evidence supporting a positive association between cognitive performance and lateralization is mixed: data from studies of fish and birds show a positive relationship whereas more limited data from studies of mammals suggest a weak or even negative relationship, suggesting the intriguing possibility of a mammal/non-mammal divide in the nature of this relationship. Here, we report an empirical test examining the relationship between lateralization and cognitive performance in wild grey squirrels (Sciurus carolinensis) by measuring left/right paw preference as a behavioural assay of cerebral lateralization and learning speed as an assay of cognitive efficiency. We carried out a motor-based laterality test using a reaching paradigm and measured learning speed on a problem-solving task. In accordance with the suggestion of a mammal/non-mammal divide, we found a negative relationship between strength of paw preference and performance on the learning task. We discuss this finding in light of niche-specific adaptations, task-specific demands and cognitive flexibility.

Management Techniques to Stimulate Oak Reproduction in Midwestern Oak Savanna Landscapes

Oak reproduction is often scarce or lacking in oak savannas under ecological restoration management, despite the fact that large canopy gaps created by the removal of invasive brush allow abundant sunlight to reach the ground surface. I conducted two experiments to investigate the effect of manipulating surface vegetation on the acorn-caching behavior of squirrels (gray squirrel Sciurus carolinensis; fox squirrel S. niger; or southern flying squirrel Glaucomys volans) and blue jays (Cyanocitta cristata). In Experiment 1, I created 10 × 10 m bare-ground patches prior to the time of acorn dispersal in restored white oak (Quercus alba) savanna and in adjacent unrestored brushy oak woods. I then compared oak seedling establishment in these bare patches the following summer to seedling establishment in unaltered tall vegetation. In Experiment 2, I used a combination of late-summer burning, tilling with an agricultural disc, and applying herbicide to create bare-ground patches adjacent to established oak woods, and then compared oak seedling establishment in these areas the following summer to that in burn-only, mow-only, and unaltered vegetation. In both experiments, oak seedling establishment was greater in areas denuded of ground vegetation. This agrees with previous research, which concluded that blue jays have a preference for storing acorns in areas of low to bare surface vegetation.

Evaluation of skin lesions of the eastern grey squirrel (Sciurus carolinensis) in forensic pathology

Evaluation of skin lesions of the eastern grey squirrel (Sciurus carolinensis) in forensic pathology

Introduced Grey Squirrels subvert supplementary feeding of suburban wild birds

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

Global distribution and status of introduced Siberian chipmunks Eutamias sibiricus

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

Comparisons of Line Transect and Point Count Survey Methods by Estimating Density of Grey Squirrel Sciurus Carolinensis

<p>The methods have used to study animal population must be defined clearly at the beginning of the project. We compared line transect and point count survey methods to estimating the density of grey squirrel at University of East Anglia campus (UEA), Norwich-United Kingdom. Across the entire UEA campus we surveyed 0.43698 ha of the 146 ha of the campus area. A total of 21 squirrels were observed during survey between 21<sup>st</sup>-26<sup>th</sup> in December 2013. Nine individuals were observed during line transect and twelve individuals were observed during point counts. The average number of species detected was differing between the two methods. Density estimates of grey squirrel from the two methods were different. Densities of grey squirrel as estimated by point count surveys were higher than those by line transect count surveys. Our results indicate that it is important to account for different survey methods when comparing the two methods to estimate the grey squirrel.</p>

Squirrelpox virus reservoir expansion on the east coast of Ireland

The European red squirrel (Sciurus vulgaris) has suffered a 20 % decline in range in Ireland since the introduction of the eastern grey squirrel (Sciurus carolinensis) in 1911. In the UK, squirrelpox virus (SQPV) has been identified as being a major contributor to the decline of red squirrel populations but has only recently been confirmed in a red squirrel from Wicklow in Ireland with anecdotal references to a previous outbreak in the Shankill area of south County Dublin and a case in Kilmacanogue, north County Wicklow. The current study examined a sample of grey squirrels from these areas for SQPV seroprevalence. Enzyme-linked immunosorbent assay (ELISA) tests were carried out on sera from 51 grey squirrels culled from two sites in south County Dublin, areas A and B, and a third site in north County Wicklow, area C. The results indicated declining SQPV seroprevalence rates moving northwards from Wicklow, 55 % in area C, 50 % in area B and 11 % in area A. The low levels of seropositivity in Killiney (A) suggest that this is the wave-front of grey squirrel expansion from Wicklow and that the population may not yet have reached the threshold density for SQPV transmission to the red squirrel population to occur. The results of this study indicate that there is potential overlap between seropositive grey squirrel populations and susceptible red squirrel populations with obvious implications for conservation and management.

Assessing the geographic origin of the invasive grey squirrel using DNA sequencing: Implications for management strategies

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.

Relative roles of grey squirrels, supplementary feeding, and habitat in shaping urban bird assemblages.

Non-native species are frequently considered to influence urban assemblages. The grey squirrel Sciurus carolinensis is one such species that is widespread in the UK and is starting to spread across Europe; it predates birds’ nests and can compete with birds for supplementary food. Using distance sampling across the urbanisation intensity gradient in Sheffield (UK) we test whether urban grey squirrels influence avian species richness and density through nest predation and competition for supplementary food sources. We also assess how urban bird assemblages respond to supplementary feeding. We find that grey squirrels slightly reduced the abundance of breeding bird species most sensitive to squirrel nest predation by reducing the beneficial impact of woodland cover. There was no evidence that grey squirrel presence altered relationships between supplementary feeding and avian assemblage structure. This may be because, somewhat surprisingly, supplementary feeding was not associated with the richness or density of wintering bird assemblages. These associations were positive during the summer, supporting advocacy to feed birds during the breeding season and not just winter, but explanatory capacity was limited. The amount of green space and its quality, assessed as canopy cover, had a stronger influence on avian species richness and population size than the presence of grey squirrels and supplementary feeding stations. Urban bird populations are thus more likely to benefit from investment in improving the availability of high quality habitats than controlling squirrel populations or increased investment in supplementary feeding.

Adenovirus: an emerging factor in red squirrel Sciurus vulgaris conservation

Abstract Adenovirus is an emerging threat to red squirrel Sciurus vulgaris conservation, but confirming clinically significant adenovirus infections in red squirrels is challenging. Rapid intestinal autolysis after death in wild animals frequently obscures pathology characteristic of the disease in animals found dead. We review the available literature to determine current understanding of both subclinical and clinically significant adenovirus infections in free‐living wild and captive red squirrel populations. Benefits of scientific testing for adenovirus incorporating both transmission electron microscopy (TEM) and polymerase chain reaction (PCR) technologies are compared and contrasted. We favour viral particle detection using TEM in animals exhibiting enteropathy at post‐mortem and the use of PCR to detect subclinical cases where no enteric abnormalities are observed. Adenoviral infections associated with re‐introduction studies are evaluated by examination of sporadic cases in wild populations and of data from captive collections used to service such studies. The paucity of data available on adenovirus infection in grey squirrel Sciurus carolinensis populations is documented, and we highlight that although subclinical virus presence is recorded in several locations in Great Britain and in Italy, no clinically significant disease cases have been detected in the species thus far. Current speculation about potential interspecific infection between sciurids and other woodland rodents such as wood mice Apodemus sylvaticus is examined. Where subclinical adenovirus presence has been detected in sympatric populations using the same point food sources, husbandry methods may be used to diminish the potential for cross‐infection. Our findings highlight the importance of controlling disease in red squirrel populations by using clearly defined scientific methods. In addition, we propose hypothetical conservation benefits of restricting contact rates between red squirrels and sympatric grey squirrels and of limiting competition from other woodland rodent species.

First finding of the chigger mite Neotrombicula talmiensis (Acari: Trombiculidae) in Italy

The first record of the chigger mite Neotrombicula talmiensis (Schluger, 1955) in Italy and on the grey squirrel Sciurus carolinensis Gmelin is reported. Four chigger specimens were found on this invasive North American squirrel species in February 2014 in the territory of Parchi di Nervi, Genoa.

Normal haematological values of African Grey Squirrel (Sciurus carolinensis)

This study evaluated the normal haematological profile of apparently healthy African grey squirrels (Sciurus carolinensis) trapped in Nsukka, Southeast Nigeria. A total of 20 squirrels comprising 8 males and 12 females were used and determination of haematological profile followed standard procedures. Results obtained for the parameters assessed are summarized as follows (mean ± standard error): packed cell volume, 37.54 ± 0.76 %; haemoglobin concentration, 14.79 ± 0.18 g/dl; red blood cell count, 7.27 ± 0.27 × 106/μl; mean corpuscular volume, 54.33 ± 1.09 fl; mean corpuscular haemoglobin, 21.74 ± 0.55 pg; mean corpuscular haemoglobin concentration, 37.39 ± 0.50 g/dl; white blood cell count, 4.77 ± 0.19 × 103/μl; neutrophil counts, 27.93 ± 1.36 %; lymphocyte counts, 67.80 ± 1.38 %; monocyte counts, 2.33 ± 0.29 %; eosinophil counts, 1.80 ± 0.26 %; basophil counts, 0.13 ± 0.09 % and body weight, 176.67 ± 3.55 g. There were no significant differences (p > 0.05) between the sexes in all the haematological parameters assessed. Results from this study was considered important as deviations in the normal haematology have a predictive value for general pathological changes in the body and may be useful in wildlife quarantine services and in active disease surveillance.

Hidden Markov models of eastern gray squirrel (Sciurus carolinensis) alarm calls

Eastern gray squirrels produce alarm calls—vocalizations used in the presence of danger that influence the behavior of some receivers. This influence is possible because the alarm calls’ rate, duration, and structure contain information about the threat and the caller. Gray squirrels’ mix of different structural call types (kuks and quaas) could contain information on potential internal influences within the squirrel. Hidden Markov models (HMMs) are ideal tools to investigate whether hidden states explain the frequencies of kuks versus quaas throughout an alarm call sequence. In this study, we compare the ability of an iid (independent and identically distributed) model and two- to six-state HMMs to represent observed sequences of kukking, quaaing, and periods of silence. Audio recordings of 44 gray squirrels were collected and the first 30 s of each alarm call sequence was coded based on spectrograms. A number of HMMs were fitted, and the overall fit of the observed sequences to each model was assessed using Akaike’s Information Criterion (AIC) and Bayesian Information Criterion (BIC), and Monte Carlo methods. The five-state HMM fit the observed call frequencies better than the other models, suggesting that the squirrels’ alarm calling sequences are influenced by a more complex temporal sequencing of acoustic units.

Coccidian parasites of red squirrels (Sciurus vulgaris) and grey squirrels (Sciurus carolinensis) in England

One hundred and ninety-three Eurasian red squirrels (Sciurus vulgaris) and 57 grey squirrels (Sciurus carolinensis) in England were examined for enteric coccidian parasites. Three species of the genus Eimeria were recovered from each host. The prevalences in S. vulgaris were Eimeria sciurorum 66%, Eimeria andrewsi 38% and Eimeria mira 2.6%; and in S. carolinensis they were Eimeria ascotensis 100%, Eimeria confusa 23% and Eimeria ontarioensis 7%.