Grey Squirrel Sciurus Carolinensis Research Articles

Assessing the potential for Grey Squirrels Sciurus carolinensis to compete with birds at supplementary feeding stations

Supplementary feeding of birds, particularly in urban areas, is often associated with increased population size and fecundity. In the UK, the non‐native Grey Squirrel Sciurus carolinensis is common in rural and urban habitats. It exploits supplementary feeders and may induce interference competition by excluding birds, but empirical evidence of this is unavailable. Using controlled model presentation experiments, we demonstrate that Grey Squirrels could reduce bird use of supplementary feeders and induce interference competition. Total bird resource use was reduced by 98% and most species exhibited similar sensitivities. The likelihood and magnitude of interference competition will depend on how rapidly displaced birds find alternative food sources; it will be greatest where there are high Grey Squirrel densities and few supplementary feeders. Other studies suggest that supplementary feeding increases Grey Squirrel numbers, and the species is also predicted to expand its non‐native range across most of Europe. Our data indicate that Grey Squirrels may eventually alter the net effect of supplementary feeding on bird populations across the European continent; increased use of squirrel‐proof feeders may help to minimize such effects.

Squirrels in suburbia: influence of urbanisation on the occurrence and distribution of a common exotic mammal

Urbanisation is widely considered to promote the establishment of non-native species, but there is limited empirical evidence of the ecological factors driving their responses. The grey squirrel Sciurus carolinensis (Gmelin 1788) is native to North America, but is widespread in the UK and is starting to spread across Europe. It is regarded as one of the world’s worst invasive animals due to its adverse impacts on native biodiversity. We use the non-native grey squirrel population in Sheffield (UK) as a case study to assess which factors limit its distribution and abundance in urban environments. In 2010 the city-wide population of adult squirrels peaked at an estimated 6539 in autumn (0.46 squirrels/ha), with maximum local densities of 8.29/ha. These densities appear to be slightly lower than those recorded in urban environments in the species’ native range. Grey squirrels occurred more frequently at urban sites with larger amounts of green-space in the surrounding region. Local habitat characteristics were, however, more powerful predictors of urban grey squirrel occurrence and abundance than regional availability of green space. Canopy cover, seed bearing trees and supplementary feeders, provided for garden birds, positively influenced grey squirrels. The potential for grey squirrels to connect city dwellers with nature thus appears to be highest in urban locations that have considerable capacity to support native biodiversity. The beneficial impacts of supplementary feeding on grey squirrel populations is notable given concerns that squirrels can adversely influence bird populations. These habitat associations also imply that grey squirrels typically respond negatively to urbanisation, which challenges arguments that urbanisation favours exotic species.

Assessing Grey Squirrel Dispersal Patterns within the Landscape Using Sequence Variation

The grey squirrel Sciurus carolinensis is thought to have contributed to the decline of red squirrel S. vulgaris populations in the UK through resource competition and disease spread. This study used mtDNA sequencing to assess patterns of grey squirrel dispersal in the UK. Patterns of genetic variation within the dloop sequence were characterised for seven grey squirrel populations. Infiltration directions and potential barriers to dispersal are identified and discussed, with a focus on Cumbria, a county at the forefront of grey squirrel expansion. Understanding the dynamics of grey squirrel dispersal will aid their management at a landscape scale and enhance the conservation of red squirrels.

The Use of Climatic Niches in Screening Procedures for Introduced Species to Evaluate Risk of Spread: A Case with the American Eastern Grey Squirrel

Species introduction represents one of the most serious threats for biodiversity. The realized climatic niche of an invasive species can be used to predict its potential distribution in new areas, providing a basis for screening procedures in the compilation of black and white lists to prevent new introductions. We tested this assertion by modeling the realized climatic niche of the Eastern grey squirrel Sciurus carolinensis. Maxent was used to develop three models: one considering only records from the native range (NRM), a second including records from native and invasive range (NIRM), a third calibrated with invasive occurrences and projected in the native range (RCM). Niche conservatism was tested considering both a niche equivalency and a niche similarity test. NRM failed to predict suitable parts of the currently invaded range in Europe, while RCM underestimated the suitability in the native range. NIRM accurately predicted both the native and invasive range. The niche equivalency hypothesis was rejected due to a significant difference between the grey squirrel’s niche in native and invasive ranges. The niche similarity test yielded no significant results. Our analyses support the hypothesis of a shift in the species’ climatic niche in the area of introductions. Species Distribution Models (SDMs) appear to be a useful tool in the compilation of black lists, allowing identifying areas vulnerable to invasions. We advise caution in the use of SDMs based only on the native range of a species for the compilation of white lists for other geographic areas, due to the significant risk of underestimating its potential invasive range.

Using GPS telemetry to validate least‐cost modeling of gray squirrel (Sciurus carolinensis) movement within a fragmented landscape

In Britain, the population of native red squirrels Sciurus vulgaris has suffered population declines and local extinctions. Interspecific resource competition and disease spread by the invasive gray squirrel Sciurus carolinensis are the main factors behind the decline. Gray squirrels have adapted to the British landscape so efficiently that they are widely distributed. Knowledge on how gray squirrels are using the landscape matrix and being able to predict their movements will aid management. This study is the first to use global positioning system (GPS) collars on wild gray squirrels to accurately record movements and land cover use within the landscape matrix. This data were used to validate Geographical Information System (GIS) least-cost model predictions of movements and provided much needed information on gray squirrel movement pathways and network use. Buffered least-cost paths and least-cost corridors provide predictions of the most probable movements through the landscape and are seen to perform better than the more expansive least-cost networks which include all possible movements. Applying the knowledge and methodologies gained to current gray squirrel expansion areas, such as Scotland and in Italy, will aid in the prediction of potential movement areas and therefore management of the invasive gray squirrel. The methodologies presented in this study could potentially be used in any landscape and on numerous species.

USING FLUORESCENCE OF BONES AND TEETH TO DETECT REMAINS OF THE EASTERN FOX SQUIRREL (SCIURUS NIGER) IN ARCHAEOLOGICAL DEPOSITS

Skeletal remains of the eastern gray squirrel (Sciurus carolinensis) and the eastern fox squirrel (S. niger) are relatively common in archaeological deposits in the eastern United States. However, the teeth and skeletons of eastern fox squirrels are very similar to those of eastern gray squirrels, which has complicated or prevented definitive assignment of these remains to the species level. As part of a comprehensive study of Pleistocene and Holocene ecology and evolution in these two species, we sought a method to assign remains to S. niger easily and definitively in mixed assemblages. Here we describe a technique (using pink fluorescence under ultraviolet [UV] light) to assign teeth and skeletons to S. niger. We examined faunal deposits from several archaeological sites and confirmed that UV fluorescence can be detected in ancient S. niger remains. This method is effective even for isolated elements (e.g., a single incisor tooth), elements that have been burned, and those that have been extremely fragmented. This technique provides an inexpensive, nondestructive test that can definitively detect S. niger in mixed faunal assemblages.

Fearing the feline: domestic cats reduce avian fecundity through trait‐mediated indirect effects that increase nest predation by other species

Summary Urban areas contain high densities of non‐native species, which in the UK include the domestic cat Felis catus (Linnaeus 1758) and the grey squirrel Sciurus carolinensis (Gmelin 1788). The direct predation effects of domestic cats on prey populations attract intense debate, and such influences of the nest‐predatory grey squirrel are receiving increasing attention. In contrast, theory predicts that sublethal and indirect effects are more important, but empirical evidence is currently lacking. We conducted controlled model presentation experiments at active urban blackbird Turdus merula (Linnaeus 1758) nests to provide the first empirical evidence that quantifies the potential sublethal and indirect effects of predators (domestic cat and grey squirrel) on avian reproductive success. Domestic cat models reduced subsequent parental provisioning rates, a strong indicator of sublethal effects, by one‐third relative to a nonpredatory rabbit Oryctolagus cuniculus (Linnaeus 1758) control. There was no compensatory increase in food load size. Previous experiments demonstrate that this magnitude of reduced food delivery will reduce nestling growth rates by c. 40%. The grey squirrel model induced similar but weaker effects. Following the brief presence of the domestic cat model, subsequent daily nest predation rates, chiefly by corvids, increased by an order of magnitude relative to the squirrel and rabbit models. The intensity of parental nest defence elicited in response to model presentations predicts the probability of such third‐party predator predation events, and the domestic cat model generated significant increases in nest defence behaviour. Synthesis and applications. The brief presence of a domestic cat at avian nest sites reduces subsequent provisioning rates and induces lethal trait‐mediated indirect effects. We provide the first robust evidence for these latter effects in any avian predator–prey system, although they are likely to be common in many avian assemblages with high predator densities. It is imperative that future assessments of the impact of predatory species on avian prey species take lethal trait‐mediated indirect effects into account, as so doing will prevent biased estimates of predator effects and facilitate the design of more effective control strategies. Full mitigation of the sublethal and indirect effects of domestic cats would problematically require permanent indoor housing.

TaqMan assays for species identification of the red squirrel (Sciurus vulgaris) and the grey squirrel (Sciurus carolinensis)

We have developed TaqMan based assays for species-specific identification of two species of squirrel found in the British Isles, the native red squirrel (Sciurus vulgaris) and the introduced north American grey squirrel (Sciurus carolinensis). These assays correctly identified tissue and hair samples of both species and there was no cross-species amplification. This is a useful method for non-invasive surveys to help conserve the red squirrel and manage the spread of the grey squirrel in the UK and Ireland.

The even darker side of the eastern gray squirrel ( Sciurus carolinensis ): a review of global introductions, invasion biology, and pest management strategies

Huynh, H.M., Bertolino, S., Lurz, P.W.W., Koprowski, J.L., Williams, G.R., Thompson, C.W., McAlpine, D.F.

Making red squirrels more visible: the use of baited visual counts to monitor populations

ABSTRACTUnderstanding changes in the distribution and abundance of the red squirrel Sciurus vulgaris in Europe, as a result of the spread of the introduced North American grey squirrel Sciurus carolinensis, is vital to planning and implementing red squirrel conservation measures. We studied the effectiveness of a variation on a common method of monitoring squirrels, standardised visual counts that made use of a diffuse baiting approach to increase their detectability. Significantly more sightings of squirrels occurred on baited than on unbaited visual transect lines in trials with the assistance of volunteers, and we recommend the use of baits in future studies.

Population change of avian predators and grey squirrels in England: is there evidence for an impact on avian prey populations?

Summary 1. Using novel analytical methods applied to extensive national bird and mammal monitoring data, we examine whether 29 English bird populations may have been depressed by increases in the abundance of two broad categories of predators. The first includes predators of juvenile and adult birds: Eurasian sparrowhawks Accipiter nisus, common kestrels Falco tinnunculus and common buzzards Buteo buteo, and the second comprises five nest predators: carrion crow Corvus corone, black-billed magpie Pica pica ,E urasian jayGarrulus glandarius, great spotted woodpecker Dendrocopos major and grey squirrel Sciurus carolinensis. 2. For 22 avian prey species, there is no evidence that increases in common avian predators and grey squirrels are associated with large-scale depression of prey abundance or population declines. For the remaining seven, some negative correlations are biologically unlikely but we cannot exclude the possibility that some of the negative associations are causally related. For example, a particularly strong negative relationship between sparrowhawk and tree sparrow during the Common Birds Census period (1967–2000) could indicate a causal relationship. In contrast, the negative association between buzzard and goldfinch during the Breeding Bird Survey period (1995–2005) is, on ecological grounds, unlikely to do so. Whilst a correlative study such as this cannot prove causation, it provides a focus for more detailed work on particular species. 3. Unexpected was a large number of positive associations between predators and prey, particularly for native avian nest predators, which largely exonerates these predators as driving declines in passerine numbers. 4. Synthesis and applications. Analyses of large-scale and extensive national monitoring data provides little underlying evidence for large-scale impacts of widespread avian predators and grey squirrels on avian prey populations, although we cannot exclude the possibility that a small number of negative associations between particular predator and prey species reflect causal relationships or that predators affect prey species at smaller spatial scales.

Potential impact of grey squirrels Sciurus carolinensis on woodland bird populations in England

Several woodland bird species have declined markedly in abundance in England over the past 40 years, whilst the grey squirrel Sciurus carolinensis, a non-native nest predator, has increased. Given the timing, there has been concern that grey squirrels have driven these declines, although there is little data to support this view. Using novel analytical methods and extensive national bird and grey squirrel monitoring data, we examine whether there is evidence that woodland bird populations in England have been depressed by grey squirrels and whether there is a relationship between nest failure and squirrel numbers. Our results indicate that grey squirrels are very unlikely to have driven observed declines of woodland birds in recent years, although the number of associations, positive as well as negative, between grey squirrels and woodland birds is greater than expected by chance. For this reason, we cannot exclude the possibility that the populations of a small number of bird species, principally increasing species, have been depressed to some degree at sites where a greater number of grey squirrels were present. Of these species, perhaps the most convincing evidence is for Common Blackbird Turdus merula and Eurasian Collared Dove Streptopelia decaocto where nest record data also identified a positive relationship between nest failure at the egg stage and squirrel abundance.

Positive relationship between non-native and native squirrels in an urban landscape

Paradoxically, non-native species sometimes displace native species that appear to be well adapted to local landscapes. That many landscapes have been altered by humans, creating habitat suitable for non-native species, helps explain this apparent paradox. We asked whether the abundance of native Douglas ( Tamiasciurus douglasii (Bachman, 1839)) and northern flying ( Glaucomys sabrinus (Shaw, 1801)) squirrels was best explained by the abundance of non-native eastern grey squirrels ( Sciurus carolinensis Gmelin, 1788), the proportion of urban development, or both using available squirrel abundance data from wildlife shelters and land-use maps. There was no evidence that non-native squirrels replaced native squirrels given that their abundances were positively related, whereas native squirrels varied negatively with the amount of development. The best model explaining variation in the abundance of Douglas and northern flying squirrels incorporated both eastern grey squirrels and development, which is consistent with the hypothesis that regional declines in native squirrels are more likely to be predicated by the alteration of native conifer habitats by humans independent of the effects of non-native squirrels.

Characteristics of a High Density Population of Southern Fox Squirrels

ABSTRACT Fox squirrel (Sciurus niger) populations in the southeastern United States are declining, with fragmentation of large mature forests believed to be the primary cause. Historically, demographics of midwestern fox squirrel or gray squirrel (Sciurus carolinensis) populations have been applied to management of southeastern fox squirrels. However, fox squirrels rarely become abundant in southeastern forests, despite variations in habitat quality. Previous research has reported on low density populations in the Southeast, but the effects of changing land use patterns on population demographics remain untested. We studied the demographics of a stable high density population of southern fox squirrels (S. n. niger) on Spring Island, South Carolina. Squirrel density (75.8 squirrels/km2), as estimated by the mark–resight method was the highest reported for fox squirrels in the Southeast. Mean annual survival rate was 62%, with automobiles causing 31% of squirrel deaths. Seasonal weights (992 g–1150 g), age ...

Urban mammals: what does the future hold? An analysis of the factors affecting patterns of use of residential gardens in Great Britain

ABSTRACTUrban areas are predicted to grow significantly in the foreseeable future because of increasing human population growth. Predicting the impact of urban development and expansion on mammal populations is of considerable interest due to possible effects on biodiversity and human‐wildlife conflict.The British government has recently announced a substantial housing programme to meet the demands of its growing population and changing socio‐economic profile. This is likely to result in the construction of high‐density, low‐cost housing with small residential gardens. To assess the potential effects of this programme, we analysed the factors affecting the current pattern of use of residential gardens by a range of mammal species using a questionnaire distributed in wildlife and gardening magazines and via The Mammal Society.Twenty‐two species/species groups were recorded. However, the pattern of garden use by individual species was limited, with only six species/species groups (bats, red foxVulpes vulpes, grey squirrelSciurus carolinensis, hedgehogErinaceus europaeus, mice, voles) recorded as frequent visitors to > 20% of gardens in the survey.There was a high degree of association between the variables recorded in the study, such that it was difficult to quantify the effects of individual variables. However, all species/species groups appeared to be negatively affected by the increased fragmentation and reduced proximity of natural and semi‐natural habitats, decreasing garden size and garden structure, but to differing degrees. Patterns of garden use were most clearly affected by house location (city, town, village, rural), with garden use declining with increasing urbanization for the majority of species/species groups, except red foxes and grey squirrels. Increasing urbanization is likely to be related to a wide range of interrelated factors, any or all of which may affect a range of mammal species.Overall, the probable effects of the planned housing development programme in Britain are not likely to be beneficial to mammal populations, although the pattern of use examined in this study may represent patterns of habitat selection by species rather than differences in distribution or abundance. Consequently, additional data are required on the factors affecting the density of species within urban environments.

Habitat and Nesting Success of Blue Jays (Cyanocitta Cristata): Importance of Scale

Abstract Nesting success of birds often is influenced by habitat features surrounding nests. However, few studies have investigated habitat influences at multiple levels and spatial scales. We examined the relationship between Blue Jay (Cyanocitta cristata) nesting success and habitat at three levels (macrohabitat, microhabitat, and nest site) and at three different scales within the microhabitat level (3.1, 0.3, and 0.07 ha circular plots surrounding nests) in central Florida. We defined successful nests as those fledging at least one offspring. An eight-fold difference in probability of nesting success existed among seven distinct macrohabitats, with Mayfield success estimates ranging from 8 to 63%. However, no difference in number of fledglings per nest existed among macrohabitats when unsuccessful nests were excluded from the analysis. Macrohabitats in which nests were more often successful had more extensive slash pine (Pinus elliottii) forest. Logistic regression analyses indicated that slash pine canopy cover was significantly related to nesting success at all three microhabitat scales, although the tree species in which a nest was placed was unimportant to nesting success. Other microhabitat and nest-site features were unrelated to nesting success. Strong circumstantial evidence indicates predation was the major cause of nest failure, but relative abundance of one potential predator, the gray squirrel (Sciurus carolinensis), was not related to nesting success in macrohabitats or slash pine canopy cover within microhabitats. In this study, logistic regression models using habitat features measured at higher levels and larger scales had better predictive power, indicating that habitat may have influenced predation at scales larger than that of a typical nest patch.

The effects of tannin and protein on food preference in eastern grey squirrels

Although some mammalian generalist herbivores avoid foods high in plant secondary compounds, it has not been adequately shown that eastern grey squirrels (Sciurus carolinensis), who regularly encounter tannin in acorns, avoid high tannin diets. Dietary tannin can inhibit nitrogen assimilation; hence herbivores that eat tannin should seek high protein diets to compensate. I presented freeranging grey squirrels with four types of dough balls that differed in tannin and protein content. Squirrels consistently preferred low to high tannin foods but did not distinguish between low and high protein foods. Intensity of preference for low tannin foods was greatest during early to mid autumn, when food is relatively abundant, and declined into the spring and early summer, when food is relatively scarce. Food availability, partitioning foraging effort between eating and scatterhoarding, physiological competence, and nutrient complementarity may explain why squirrels consume tannin in natural diets, in spite of preference for low tannin dough balls demonstrated here.

Resource patch array use by two squirrel species in an agricultural landscape.

Eastern grey squirrels (Sciurus carolinensis) and North American red squirrels (Tamiasciurus hudsonicus) were studied among wooded patches within an agricultural mosaic. Fifteen sites south of Ottawa, Canada, with differing landscape and local features were censused using tracking boards placed in a woods or wooded fencerow. Regression analyses of landscape compositional and physiognomic variables within a 1-km radius isolated the best predictors of grey and red squirrel abundance and activity. Grey squirrels were found in both small woods and fencerows in farm landscapes but were not found in large woods. A polynomial regression of wooded patch size explained 79% of the variance in grey squirrel abundance. Grey squirrel activity was correlated with the percent cover of soybeans in the landscape. Red squirrels were found in fencerows, small and large woods; activity was correlated with the percent cover of both woods and corn crop in the surrounding landscape. These results indicate that distributions of both species are influenced by multiple landscape elements, but that grey squirrels may rely on fragmented agricultural landscapes whereas red squirrels make more use of both native woodland and altered landscapes.

Study of diseases of the grey squirrel (Sciurus carolinensis) in Italy. First isolation of the dermatophyte Microsporum cookei

Study of diseases of the grey squirrel (Sciurus carolinensis) in Italy. First isolation of the dermatophyte Microsporum cookei

Breeding season diet of the Goshawk Accipiter gentilis in Wales

Information on the diet of the Goshawk Accipiter gentilis during the breeding season was collected in Wales during 1991–1993. Diet consisted mainly of birds (87%) and mammals (13%). Forty‐five prey species were collected, ten of which were important in numerical or biomass terms: Feral Pigeon Columba livia, Woodpigeon Columba palumbus, Crow/Rook Corvus coronet Corvus frugilegus, Magpie Pica pica, Jay Garrulus glandarius, Mistle Thrush Turdus viscivorus, Song Thrush Turdus philomelos, Blackbird Turdus merula, Grey Squirrel Sciurus carolinensis and Rabbit Oryctolagus cuniculus. Pigeon biomass was important throughout the breeding season and was more important in the diet of nesting Goshawks on higher ground (>250 m). On lower ground, corvids, mammals and pigeons were the main contributors to the Goshawk diet. Rabbits were more frequently taken at lower nesting territories, and thrushes occurred at all altitudes. Mammals, particularly Grey Squirrel, were found in higher numbers in the diet of Goshawks nesting in small woods (<1000 ha) compared with the diet of Goshawks nesting in two large forests (c. 3500 ha and c. 6100 ha). Goshawks preyed upon juvenile Woodpigeons, corvids and thrushes, and switched from young thrushes to young corvids as the latter became available. Predation peaks on young birds corresponded with the presence of nestling Goshawks in late May to early July. Predation of juvenile prey led to a decrease in mean prey item mass (April‐May, 437 g; July, 376 g). No evidence was found to suggest that sexual size dimorphism in Goshawks resulted in partitioning of prey captured during the breeding season. Differences found were probably due to local abundance and vulnerability of prey species rather than specific selection by the two sexes.