Sciurus Carolinensis Research Articles

American Marten (<i>Martes americana</i>) and Northern Goshawk (<i>Accipiter gentilis</i>) simultaneously attack Gray Squirrel (<i>Sciurus carolinensis</i>)

A Northern Goshawk (Accipiter gentilis) was observed following an American Marten (Martes americana). The marten’s attempts to capture a Gray Squirrel (Sciurus carolinensis) forced the squirrel into the open where the goshawk repeatedly attempted to capture it as the marten chased it through the trees. Attacks on prey flushed by heterospecific predators have been reported for a few other raptors, but this type of interaction has not been reported previously for either goshawks or martens.

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.

At a fine scale, hardwood patches support wildlife diversity in longleaf pine woodlands

AbstractRestoring and maintaining biodiversity in a changing world is increasingly challenging due to the competing needs of species for suitable space and resources. One ecosystem that has seen considerable anthropogenic changes in extent and structure is the longleaf pine (Pinus palustris) ecosystem. Understanding how wildlife responds to restoration is important to informing forest restoration and conservation. We monitored game birds and mid‐large‐sized mammal occupancy in and around hardwood patches embedded within a longleaf pine woodland at The Jones Center at Ichauway in Newton, GA. We found that 11 species use the transition zone between the longleaf pine and hardwood hammocks. Gray squirrels (Sciurus carolinensis), Virginia opossums (Didelphis virginiana), and nine‐banded armadillos (Dasypus novemcinctus) occupancy increased along the gradient while fox squirrel (Sciurus niger) declined. Our results suggest that oak patches and transitional zones are important to maintaining biodiversity within the longleaf pine ecosystem.

Climatic niche and range shifts of grey squirrels (Sciurus carolinensis Gmelin) in Europe: An invasive pest displacing native squirrels.

As an invasive pest from North America, grey squirrels (GSs; Sciurus carolinensis Gmelin) are displacing native squirrels in Europe. However, the climatic niche and range dynamics of GSs in Europe remain largely unknown. Through niche and range dynamic models, we investigated climatic niche and range shifts between introduced GSs in Europe and native GSs in North America. GSs in North America can survive in more variable climatic conditions and have much wider climatic niche breadth than do GSs in Europe. Based on climate, the potential range of GSs in Europe included primarily Britain, Ireland, and Italy, whereas the potential range of GSs in North America included vast regions of western and southern Europe. If GSs in Europe could occupy the same climatic niche space and potential range as GSs in North America, they would occupy an area ca. 2.45 times the size of their current range. The unfilling ranges of GSs in Europe relative to those of GSs in North America were primarily in France, Italy, Spain, Croatia, and Portugal. Our observations implied that GSs in Europe have significant invasion potential, and that range projections based on their occurrence records in Europe may underestimate their invasion risk. Given that small niche shifts between GSs in Europe and in North America could lead to large range shifts, niche shifts could be a sensitive indicator in invasion risk assessment. The identified unfilling ranges of the GS in Europe should be prioritized in combating GS invasions in the future. © 2023 Society of Chemical Industry.

Behavioral adaptations of scatterhoarders to seasonal flooding

Scatterhoarder responses to factors that influence stored food (i.e., flooding) is important given the strong reliance on hoarded food for survival. We examined how eastern gray squirrels ( Sciurus carolinensis, Gmelin 1778) have adapted to a seasonally flooded ecosystem in Alabama. Our study area was dry September–November and flooded the rest of the year. We predicted squirrels would respond to flooding by storing food in areas that stay dry during winter, seasonally shifting to dry habitat, or decreasing the amount of hard mast in their winter diet. We also examined previously reported survival differences between the dry and flooded seasons. During the dry season, 72% of acorns were buried in areas that later flooded. Habitat use did not change significantly during the flooded and dry seasons; however, squirrels used habitat that stayed dry during flooding to a greater degree during non-flood seasons. The amount of hard mast in the diet did not change significantly between the dry and flooded seasons. However, squirrels were more likely to die during the flooded season ( P = 0.02). We did not find any behavioral adaptations to seasonal flooding. Further research is needed to fully understand the effects of fluctuating environmental conditions on scatterhoarders.

Jumping performance in tree squirrels: Insights into primate evolution

Morphological traits suggesting powerful jumping abilities are characteristic of early crown primate fossils. Because tree squirrels lack certain ‘primatelike’ grasping features but frequently travel on the narrow terminal branches of trees, they make a viable extant model for an early stage of primate evolution. Here, we explore biomechanical determinants of jumping performance in the arboreal Eastern gray squirrel (Sciurus carolinensis, n = 3) as a greater understanding of the biomechanical strategies that squirrels use to modulate jumping performance could inform theories of selection for increased jumping ability during early primate evolution. We assessed vertical jumping performance by using instrumented force platforms upon which were mounted launching supports of various sizes, allowing us to test the influence of substrate diameter on jumping kinetics and performance. We used standard ergometric methods to quantify jumping parameters (e.g., takeoff velocity, total displacement, peak mechanical power) from force platform data during push-off. We found that tree squirrels display divergent mechanical strategies according to the type of substrate, prioritizing force production on flat ground versus center of mass displacement on narrower poles. As jumping represents a significant part of the locomotor behavior of most primates, we suggest that jumping from small arboreal substrates may have acted as a potential driver of the selection for elongated hindlimb segments in primates, allowing the center of mass to be accelerated over a longer distance—and thereby reducing the need for high substrate reaction forces.

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.

Comparative, anatomical and histological study of spleen in two Iraqi vertebrates weasel (Herpestes javanicus) and Eastern gray squirrel (Sciurus carolinensis)

Comparative, anatomical and histological study of spleen in two Iraqi vertebrates weasel (Herpestes javanicus) and Eastern gray squirrel (Sciurus carolinensis)

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.

Using blood lead concentrations of wildlife sentinels to identify environmental risk factors of lead exposure for public health and wildlife rehabilitation efforts.

Lead poisoning remains a persistent health issue for both humans and wildlife, despite strides to reduce lead contamination in the environment. Using Geographic Information Systems (GIS), this study explores the associations between blood lead levels (BLLs) in wildlife sentinels and possible built environment lead exposure risk factors in the Minneapolis-Saint Paul, Minnesota urban area. Results show a high-level of heterogeneity in animal BLLs (n = 472) across our urban environment and suggest that each kilometer increase in road density is associated with a 17.07% (95% CI: 1.48%, 35.05%) increase in BLL in our study species of Virginia opossums and Eastern gray squirrels, and a 14.28% (95% CI: 1.16%, 29.09%) increase in BLL of rock pigeons. For squirrels and opossums, we see an additional 5.72% (95% CI: 0.59%, 10.85%) increased risk of BLL for every 1000 people per square-mile. The relationship between animal sentinels and environmental hazards can give us an insight into the potential lead exposure risks for humans. The use of wildlife sentinel data to explore environmental risk factors supports a One Health approach to better address public health questions and aid in wildlife rehabilitation related to residual lead poisoning from ambient environmental exposures.

Evidencing success: Data requirements to model the impacts of long-term management of invasive squirrels

Established widespread populations of invasive vertebrates can be challenging to eradicate and for small to medium-sized vertebrates, such as squirrels, is often not deemed feasible. However, long-term trapping campaigns are necessary to limit spread or reduce impacts. The scale of trapping programmes is often limited by budgets that are not commensurate to the scale of the problem. On-going costs and fundraising are key factors used by decision makers to assess the feasibility of complete removal or long-term management options of established populations. Predicting the time and effort required to successfully manage Invasive Alien Species (IAS) remains a challenge, particularly where different strategies need to be employed across different spatial scales and habitat types, and in response to changing population densities. Statistical methods such as removal models can be applied to quantify population abundance during management operations and could inform planning of resource requirements. However, in practice, the lack of awareness of data requirements results in unsuited or non-standardized data collection. We present data from an invasive grey squirrel (Sciurus carolinensis) management project in the United Kingdom as a case study to illustrate common issues that impact on quantifying project outcomes. We focus on human and operational aspects of implementation and suggest ways of prioritizing analytical requirements. Insights consider conservation targets, data collection and operational design and may be of relevance to stakeholders, analysts, field operators and managers.

Impact of exposure to urban air pollution on grey squirrel (Sciurus carolinensis) lung health

The increased rate of global urbanisation has recently exacerbated the significant public health problem of traffic related air pollution. Despite the known significant impact on human health, little is known about the effects of air pollution on wildlife health. The lung is the primary target organ for the effects of exposure to air pollution, leading to lung inflammation, altering the lung epigenome, culminating in respiratory disease. In this study, we aimed to assess lung health and DNA methylation profiles in Eastern grey squirrel (Sciurus carolinensis) populations living across an urban-rural air pollution gradient. Squirrel lung health was assessed in four populations situated across the most polluted inner-city boroughs to the less polluted edges of Greater London. We also assessed lung DNA methylation across three London sites and a further two rural sites in Sussex and North Wales. Lung and tracheal diseases were present in 28% and 13% of the squirrels respectively. Specifically, focal inflammation (13%), focal macrophages with vacuolated cytoplasm (3%) and endogenous lipid pneumonia (3%). There was no significant difference in prevalence of lung, tracheal diseases, anthracosis (carbon presence) or lung DNA methylation levels between urban sites and urban and rural sites respectively or NO2 levels. BALT (Bronchus-Associated Lymphoid Tissue) was significantly smaller in the site with highest NO2 and contained the highest carbon loading compared to sites with lower NO2, however differences in carbon loading in between sites were not significant. High pollution site individuals also had significantly higher numbers of alveolar macrophages which suggests that grey squirrels are exposed to and respond to traffic-related air pollution and further research is needed to understand the impact of traffic-related air pollutants on wildlife health.

Increasing Detections of Small to Medium-Sized Mammals Using Multiple Game Cameras

Surveys using game cameras have become a standard method to determine presence of small to medium-sized mammals such as Spilogale putorius (Eastern Spotted Skunk). Surveys typically use a single camera at each site; however, prior work with other species suggests that single cameras are less likely than multiple cameras to detect small and mid-size mammals. During the winters of 2019–2020 and 2020–2021, we placed 71 camera stations in the Arkansas Ozarks, with each station having 2 cameras aimed at the same target. We used detections of a common species, Sciurus carolinensis (Eastern Gray Squirrel), to determine if adding an additional camera at each site could increase detections of animals similar in size. Overall, detections increased 27% with the addition of a second camera. We found that a second camera increased Eastern Gray Squirrel detections by 15.6% when the animal was closer than 1 body-length from the target bait tree and 41.2% when the animal was more than 1 body-length from the bait tree. We conclude that a single camera may miss a significant number of detections of small to medium-sized animals and could bias results of detection/non-detection studies.

Masticatory biomechanics of red and grey squirrels (Sciurus vulgarisandSciurus carolinensis) modelled with multibody dynamics analysis

The process of feeding in mammals is achieved by moving the mandible relative to the cranium to bring the teeth into and out of occlusion. This process is especially complex in rodents which have a highly specialized configuration of jaw adductor muscles. Here, we used the computational technique of multi-body dynamics analysis (MDA) to model feeding in the red (Sciurus vulgaris) and grey squirrel (Sciurus carolinensis) and determine the relative contribution of each jaw-closing muscle in the generation of bite forces. The MDA model simulated incisor biting at different gapes. A series of 'virtual ablation experiments' were performed at each gape, whereby the activation of each bilateral pair of muscles was set to zero. The maximum bite force was found to increase at wider gapes. As predicted, the superficial and anterior deep masseter were the largest contributors to bite force, but the temporalis had only a small contribution. Further analysis indicated that the temporalis may play a more important role in jaw stabilization than in the generation of bite force. This study demonstrated the ability of MDA to elucidate details of red and grey squirrel feeding biomechanics providing a complement to data gathered via in vivo experimentation.

Modelling the management of an invasive species at landscape scale: are oral contraceptives the missing ingredient for success?

Context Invasive non-native species are on the rise worldwide, exacerbating already significant environmental and economic impacts. Concurrently, public attitudes towards methods of controlling these species are changing, with greater demand for non-lethal solutions. This has fostered research into developing new, effective technologies and strategies for wildlife management. Aims On the basis of a case study focusing on the eastern grey squirrel (Sciurus carolinensis) in the UK, this study aimed to understand the potential for population management, using either live trapping or oral contraception. First, assuming completely coordinated landscape-scale control, and then, coordinated control only on parts of the landscape, accounting for the potential that landowners’ attitudes towards alternative methods may differ and reflect those of the wider public. Methods We used an existing spatially explicit individual-based modelling approach applying various parameterisations to define management. We varied the density of traps or hoppers delivering contraceptives, the duration of deployment, contraceptive efficacy, initial population size, and the probability of landowner participation. The latter was based on a previous public survey, suggesting that 40% of the respondents were open to management using trapping and 64% to using contraception. Key results With complete coordinated control, trapping was generally faster and more cost-effective than was contraception. However, when differences in social acceptance were considered, reducing participation and, consequently, the spatial coverage of management, contraception was found to maintain greater population reductions than was trapping with similar effort, assuming a contraceptive efficacy of 75% or higher. Conclusions This study added another layer of complexity to managing invasive non-native species, namely the potential effect that landowners’ attitudes to different methods of population management might have on the level of coordinated control at landscape scale. In a situation such as the one modelled by this study, where management is not a legal requirement, this human dimension must be considered alongside cost-effectiveness, to develop successful control in line with management goals. Implications Further work is required to establish the actual attitudes of landowners, and in different contexts (e.g. urban, rural areas), how this may change as new approaches become available, and then how spatial variation (clustering) in the resulting wildlife population control may affect outcomes.

Factors affecting bait uptake by the grey squirrel (Sciurus carolinensis) and the future delivery of oral contraceptives

Context Invasive species negatively affect natural communities and human activities. The grey squirrel is an invasive species in the UK, causing damage to forestry and the decline of the native red squirrel. Oral contraceptives have the potential to reduce numbers of grey squirrels; however, to be effective a sufficient proportion of a population must consume a bait containing contraceptives. Aims The objective of this study was to estimate the efficacy of delivering baits via feeders to grey squirrels and to determine the factors most important to bait uptake. Methods Bait uptake was measured using the bait marker Rhodamine B mixed with 100% hazelnut butter and delivered to grey squirrels via purpose-designed feeders. Different concentrations of Rhodamine B were first trialled on captive grey squirrels for their palatability and detectability in the hair. Bait-uptake field trials were then conducted in 10 UK woodlands by using the preferred concentration. Key results In captive trials, it was found that a concentration of 0.18% Rhodamine B mixed in hazelnut butter was palatable to grey squirrels and that individuals needed to consume only small amounts (<5 g) for it to be detected in the flank hair by using an ultraviolet microscope. It was possible to deliver bait to the majority of grey squirrels in 6 of 10 woods within 4 days. Season, feeder density and squirrel density were important factors affecting bait uptake, with more squirrels consuming bait in summer than in winter and from three feeders per hectare rather than from one per hectare. Conclusions This study demonstrated that baits delivered via feeders can target the majority of grey squirrels in woodland environments. Implications Oral contraceptives could offer a cost-effective tool to reduce numbers of grey squirrels across the UK landscape and mitigate the negative impacts they have on native wildlife and tree health.

Mammals of Hazeldell Nature Preserve, Pulaski County, Kentucky: A Rare Highland Rim Ecosystem

Hazeldell Nature Preserve is a rare ecosystem on the Highland Rim of south-central Kentucky. It is the only state-protected site of its kind. This preserve is comprised of two distinct plant communities, including wet flatwoods and wet meadow. Despite its uniqueness, no ecological studies have been conducted on mammals in the past. Currently, two separate studies are underway on mammals. Here we present the results from the first of these that used camera traps set in the wet flatwoods community from 1 February to 28 March 2020. A total of 34,071 photos were taken with 553 having images of 12 species of mammals. The four most photographed species were eastern gray squirrel, Virginia opossum, white-footed deermouse, and white-tailed deer. These four species appeared in 91% of photos. The remaining 49 photos were of eight species including: eastern cottontail, coyote, bobcat, northern raccoon, striped skunk, southern flying squirrel, common gray fox, and eastern fox squirrel. Woodchuck and eastern chipmunk were not photographed during the study, yet each have ranges that include the preserve. These burrowers may avoid the preserve because of the secondary water table and saturated soil that occur during extended periods. The results of this study serve as baseline data for comparison to future camera trapping. Continued photo documentation will be used to identify changes in the mammal species composition of the preserve caused by species range changes in response to various factors, including habitat fragmentation and climate change.

Biological invasions disrupt activity patterns of native wildlife: An example from wild pigs

Activity patterns are an important behavioral trait linked to animal interactions within food webs. Biological invasions can have impacts on the behavior of native species through predation and competition, but few studies have determined if invasions lead to shifts in activity patterns of native species. Wild pigs (Sus scrofa) are a generalist, invasive vertebrate in North America that may affect activity patterns of native species through competition and predation. We hypothesized native species' activity patterns would differ from their expected activity pattern (i.e., typical hours of daily activity) and be more variable across sites occupied by wild pigs. We used a U.S. nationwide and a regional camera trapping dataset to determine if wild pig presence affected activity patterns of a nocturnal, diurnal, and crepuscular species: northern raccoon (Procyon lotor), eastern gray squirrel (Sciurus carolinensis), and white-tailed deer (Odocoileus virginianus), respectively. We simulated expected activity patterns of each species and overlapped them with observed activity patterns of respective species in populations where wild pigs were present and where they were not detected. Overlap coefficients were used in generalized linear mixed models to determine if wild pig presence explained deviations from the expected activity pattern. When wild pigs were detected, raccoons remained nocturnal, but their activity patterns were less variable, squirrel activity on the ground was less diurnal and their activity patterns were more variable, and deer activity patterns remained similar in both respects. These results highlight how biological invasions may differentially influence native species activity patterns, potentially altering food web-level interactions.

Indirect effects of pine marten recovery result in benefits to native prey through suppression of an invasive species and a shared pathogen

Invasive species pose a major threat to native species, both through direct interactions, such as competition for resources, and indirect interactions, such as when the invasive species acts as a reservoir host for a virulent pathogen. Recent research has indicated that the recovery of native predators can benefit native prey species that compete with invasive prey, in circumstances where predation is more pronounced on the naïve invasive species. We use the native red squirrel (Sciurus vulgaris), invasive grey squirrel (Sciurus carolinensis) and shared squirrelpox virus (SQPV) system in North Wales, UK, as a case study system to assess the impact of a recovering, native predator of both squirrel species, the pine marten (Martes martes), on community structure. We develop a stochastic, spatial model that represents the habitat structure, distribution, and connectivity in North Wales and models the interactions of red and grey squirrels, SQPV, and pine marten to examine the indirect effect of native predator recovery on competitively linked native-invasive prey species and a viral pathogen. Our model demonstrates the potential role of native predators in reversing the replacement of a threatened native prey through the regulation of the invasive prey species due to sustained predation, and the resultant extirpation of a viral pathogen, which otherwise catalyses the replacement of the native red squirrel by the invasive grey squirrel. Our findings have system specific applied conservation implications, but moreover demonstrate the critical role of native predators in mitigating the impacts of invasive species and, indirectly, the infectious diseases they harbour.