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Microbiota inhabiting the gastrointestinal (GI) tract of animals has important impacts on many host physiological processes. Although host diet is a major factor influencing the composition of the gut micro‐organismal community, few comparative studies have considered how differences in diet influence community composition across the length of the GI tract. We used 16S sequencing to compare the microbiota along the length of the GI tract in Abert's (Sciurus aberti) and fox squirrels (S. niger) living in the same habitat. While fox squirrels are generalist omnivores, the diet of Abert's squirrels is unusually high in plant fiber, particularly in winter when they extensively consume fiber‐rich inner bark of ponderosa pine (Pinus ponderosa). Consistent with previous studies, microbiota of the upper GI tract of both species consisted primarily of facultative anaerobes and was less diverse than that of the lower GI tract, which included mainly obligate anaerobes. While we found relatively little differentiation between the species in the microbiota of the upper GI tract, the community composition of the lower GI tract was clearly delineated. Notably, the Abert's squirrel lower GI community was more stable in composition and enriched for microbes that play a role in the degradation of plant fiber. In contrast, overall microbial diversity was higher in fox squirrels. We hypothesize that these disparities reflect differences in diet quality and diet breadth between the species.

Individual variation in behaviour can contribute to the heterogeneous distribution of parasites among hosts for example by affecting the probability of encountering infective stages (larvae). Here, we investigated the relationship between host boldness/exploration tendency and gastro-intestinal helminth infection in invasive Eastern grey squirrels (Sciurus carolinensis). We used direct helminth counts, data rarely available in host-parasite studies that often used less reliable indirect estimates of infection. We predicted that bolder animals with a strong exploration tendency will have higher parasite load than shy, less explorative hosts. We examined two parameters of parasite infection: infection status and intensity of infection. Individual personality of 207 grey squirrels was assessed by capture-mark-recapture (CMR), calculating the trappability and trap diversity indices as estimates of boldness and exploration, respectively. Since both indices were strongly correlated, we used PCA to derive a single score (first component) which had a high value for bold, exploring animals. At the end of the study, 77 individuals were euthanized and gastro-intestinal helminths were identified and counted. Overall 73% of grey squirrels were infected by Strongyloides robustus with the intensity of infection varying from 1 to 86 worms (mean ± SE = 10.7 ± 2.1 helminths per host). We found that bolder, more explorative animals were more likely to be infected by S. robustus. However, host personality was not related to parasite intensity, which was instead positively associated with host body mass. Our results confirm that differences in personality-related host behaviour can influence the distribution of infections within host populations and stimulate further questions on whether such personality-parasite relationships may affect the invasion process.

Knowledge of which population parameters and mortality risks contribute most to population decline and endangerment is necessary to develop informed and actionable conservation plans for threatened and endangered species (Rushton et al., 2006). The federally endangered Mount Graham red squirrel (Tamiasciurus fremonti grahamensis) is restricted to the Pinaleno Mountains, in southeastern Arizona, USA. The population is critically threatened with extensive habitat loss from fire as well as by an introduced non-native squirrel species, the Abert's squirrel (Sciurus aberti). Recovery is challenged by low survival and poor reproduction, such that the subspecies is functionally semelparous. We calculate survival rates and cause-specific mortality hazards from known-fate individuals to understand the impact of predation on survival and demography in this peripheral population. We document the lowest survival and highest rates of mortality in any population of North American red squirrels in both adult and juvenile age classes (mean annual survival: adults = 0.32, juveniles = 0.26). We attributed the majority of confirmed deaths to avian predation (adults 65%, juveniles 75%), and the daily hazard rate for avian predation was 15 times higher than for mammalian predation and 2 times higher than death from unknown causes. It is likely that the presence of an ecologically similar, non-native tree squirrel subsidizes a diverse avian predator guild, which includes two raptor species of conservation concern. In addition to efforts to remove the non-native Abert's squirrel, we recommend immediate forest restoration efforts in the long term, and habitat augmentation to increase structural complexity, cover, shelter, and food resources in the short term.

The present study was undertaken to describe Cryptosporidium spp. infection in tree squirrels from 17 locations in Northern Italy. A total of 357 squirrels were examined, including species native to Europe (Sciurus vulgaris; n = 123), and species introduced from North America (Sciurus carolinensis; n = 162) and Southeast Asia (Callosciurus erythraeus; n = 72). Faecal samples of all squirrels were examined for the presence of Cryptosporidium infection by microscopy (flotation method) and PCR/sequence analysis of the Cryptosporidium 18S rRNA, actin, and gp60 genes. Despite the overlapping ranges of native and introduced tree squirrel species in the study area, they host different Cryptosporidium spp. Sciurus vulgaris were exclusively infected with Cryptosporidium ferret genotype (n = 13) belonging to three novel gp60 subtypes, VIIIb–VIIId. Sciurus carolinensis hosted C. ubiquitum subtype XIIb (n = 2), Cryptosporidium skunk genotype subtype XVIa (n = 3), and chipmunk genotype I subtype XIVa (n = 1). Cryptosporidium chipmunk genotype I subtype XIVa was also found in two C. erythraeus. Comparing data from this and previous studies, we propose that Cryptosporidium skunk genotype and possibly C. ubiquitum subtype XIIb were introduced to Europe with eastern grey squirrels. Cryptosporidium chipmunk genotype I and ferret genotype were associated with high intensity infections, but there was no association with diarrhoea.

The American red squirrel (Tamiasciurus hudsonicus Exrleben) and northern flying squirrel (Glaucomys sabrinus Shaw) are important mammal species in coniferous forests that are widely distributed across temperate and boreal ecological zones. Although T. hudsonicus and G. sabrinus apparently prefer late-successional forests, their population dynamics show no clear pattern in young second-growth and old-growth conifer forests. We used a compilation of study results that had standardized methodology and sampling effort to compare tree squirrel responses across a range of forest conditions. We tested the hypotheses (H) that abundance, reproduction, recruitment, and survival would be higher in (H1) old-growth than second-growth stands, (H2) unthinned than thinned second-growth stands, and (H3) lightly than heavily thinned stands. Tree squirrel populations in old-growth stands were considered the “standard” treatment to which other treatments in second-growth stands (unthinned and variously thinned) were compared. Thinned stands were grouped into low, medium, and high densities of trees. Datasets from seven published studies included 2804 Tamiasciurus and 837 G. sabrinus individuals, 25 study years, and 158 trapping periods. Mean abundance of Tamiasciurus was similar among treatment stands, ranging from 0.62 to 1.29·ha−1. Mean numbers of G. sabrinus were highest in old-growth stands at 0.65·ha−1, followed by the low- and medium-density stands at 0.50·ha−1, the high-density stands at 0.25·ha−1, and finally the unthinned second-growth stands at a low of 0.12·ha−1. In terms of effect size, mean proportional change in abundance, relative to that within old-growth stands, of both squirrel species in the three thinned stands were within the range of natural fluctuations in old-growth stands. Populations of Tamiasciurus in the unthinned stands were not within the range of fluctuations in the old-growth stands. Mean number of successful pregnancies and total recruits were similar among stands for Tamiasciurus, with variability in female breeding and winter survival. Mean number of recruits of G. sabrinus was highest in old-growth stands with no other differences in demographic attributes among stands. The biological significance of these differences in demographic variables was small in terms of effect sizes. Tamiasciurus and G. sabrinus seem to persist in a relatively broad range of young managed forest habitats, as well as in old-growth stands.

Eastern fox squirrels (Sciurus niger), reddish-brown tree squirrels native to the eastern and southeastern United States, were introduced to and now thrive in suburban/urban California. As a result, many residents in the greater Los Angeles region are grappling with living amongst tree squirrels, particularly because the state’s native western gray squirrel (Sciurus griseus) is less tolerant of human beings and, as a result, has historically been absent from most sections of the greater Los Angeles area. ‘Easties,’ as they are colloquially referred to in the popular press, are willing to feed on trash and have an ‘appetite for everything.’ Given that the shift in tree squirrel demographics is a relatively recent phenomenon, this case presents a unique opportunity to question and re-theorize the ontological given of ‘otherness’ that manifests, in part, through a politics whereby animal food choices ‘[come] to stand in for both compliance and resistance to the dominant forces in [human] culture’. I,...

Microsciurus flaviventer ([Gray, 1867][1]) is a Neotropical tree squirrel commonly known as the Amazon dwarf squirrel. Small bodied with dark brown dorsal pelage contrasted with a gray or yellowish gray venter, and a faintly banded tail. M. flaviventer is 1 of 4 species in the genus Microsciurus . The geographic range of M. flaviventer extends from the Amazon basin of South America throughout western and southeastern Colombia, Ecuador, southern Peru, Brazil west of Rio Negro, and Madeira. It is most commonly associated with evergreen lowland tropical rainforest. Status of M. flaviventer is “Data Deficient” under the International Union for Conservation of Nature and Natural Resources Red List of Threatened Species ; however, loss of habitat is a major concern. [1]: #ref-18

The eastern grey squirrel (EGS), Sciurus carolinensis, is a tree squirrel native to the eastern United States. This species commonly presents to wildlife medical clinics for a variety of human-related injuries including confrontations with road traffic and pet predation. The purpose of this study was to assess initial examination findings as prognostic indicators for survival in EGS. The medical record database of the University of Illinois Wildlife Medical Clinic was searched from January 2012 through December 2018 for records of EGS weighing

Wildlife-associated Cryptosporidium are an emerging cause of cryptosporidiosis in humans. The present study was undertaken to determine the extent to which North American tree squirrels and ground squirrels host zoonotic Cryptosporidium species and genotypes. Fragments of the Cryptosporidium 18S rRNA and actin genes were amplified and sequenced from fecal samples obtained from three tree squirrel and three ground squirrel species. In tree squirrels, Cryptosporidium was identified in 40.5% (17/42) of American red squirrels (Tamiasciurus hudsonicus), 40.4% (55/136) of eastern gray squirrels (Sciurus carolinensis), and 28.6% (2/7) of fox squirrels (Sciurus niger). Human-pathogenic Cryptosporidium ubiquitum and Cryptosporidium skunk genotype were the most prevalent species/genotypes in tree squirrels. Because tree squirrels live in close proximity to humans and are frequently infected with potentially zoonotic Cryptosporidium species/genotypes, they may be a significant reservoir of infection in humans. In ground squirrels, Cryptosporidium was detected in 70.2% (33/47) of 13-lined ground squirrels (Ictidomys tridecemlineatus), 35.1% (27/77) of black-tailed prairie dogs (Cynomys ludovicianus), and the only golden-mantled ground squirrel (Callospermophilus lateralis) that was sampled. Cryptosporidium rubeyi and ground squirrel genotypes I, II, and III were identified in isolates from these ground squirrel species. In contrast to the Cryptosporidium infecting tree squirrels, these species/genotypes appear to be specific for ground squirrels and are not associated with human disease.

Southern California is home to one native and one introduced species of tree squirrel. The native Western Gray Squirrel (Sciurus griseus; here on gray squirrel), is a highly arboreal tree squirrel that can be found inhabiting mixed oak and pine forest habitats and tree dominated parks and gardens in suburban areas within California (King 2004; Muchlinski et al. 2009). Gray squirrels feed primarily on fungi, pine nuts, acorns, and bay fruit. They have also been documented to feed on Eucalyptus seeds, samaras, and berries (Morus and Phoradendron spp.) along with bird eggs and nestlings (Carraway and Verts 1994). Fungi are one of the gray squirrel’s most highly utilized food items. By consuming fungi, gray squirrels assist in providing a healthy soil environment for the development and growth of oak-woodland communities (Maser et al. 1981). The introduced Eastern Fox squirrel (Sciurus niger; here on fox squirrel) is an invasive generalist species (Tatina 2007) typically found in upland areas, open forests, or areas neighboring open spaces such as agricultural lands and pastures (Sexton 1990). The presence of the fox squirrel in California has been a concern of the general public, land managers, and researchers. The Los Angeles County Agricultural Commission considers the fox squirrel a pest species and potentially aggressive. In their native range, the fox squirrel has been important ecologically in the succession of grasslands to forests by caching their food within open grasslands (Stapanian and Smith 1986). Seeds cached and fed on by the fox squirrel come from persimmon, blue gum Eucalyptus, cottonwood, pines, and many others (Koprowski 1994). Fox squirrels incorporate animal foods in their diet such as insects, butterflies, ants, birds, and bird eggs (Koprowski 1994). It is reported that the fox squirrel takes advantage of fruits found within backyards such as avocados, oranges, and strawberries, an activity often disliked by human occupants (Becker and Kimball 1947; Salmon et al. 2005). Very little is known regarding food preferences of the two species within Southern California and detailed information is limited. This study sought to gain information on what foods each species selects, and which food items overlap and differ between gray and fox squirrels. Knowledge of food preferences among species promotes making management decisions that sustain their populations. For example, improving habitat by adding particular plants or trees preferred by the gray squirrel can aid in the recovery of its population (Linders and Stinson 2006). Information on food selection may also reveal a high degree of overlap such that competition is possible in years of food shortage. Competition could lead to extirpation of the gray squirrel where food selection is limited. Muchlinski et al. (2009) established that fox squirrels replace gray squirrels at locations

Restoration of the functionally extirpated American chestnut (Castanea dentata) to landscapes of the eastern United States is planned with the successful propagation of a blight-resistant hybrid tree. Predicting the response of rodent seed consumers to this novel source of mast will be critical to restoration success, as rodents are important seed predators and dispersers in forests that once included chestnut. In particular, frequency-dependent foraging responses by rodents could affect the rate of spread of rare chestnuts following reintroductions. We conducted field trials to test for seed preferences and frequency-dependent selection by fox squirrels (Sciurus niger) when combinations of American chestnut and two common associates [northern red oak (Quercus rubra) and white oak (Q. alba)] were available in varying frequencies. Fox squirrels tended toward positive frequency-dependent seed predation when combinations of white oak and chestnuts were available, consuming more common mast items at a higher rate than expected based on availability. No preferences were observed between American chestnut and either red or white oak independent of frequency, but red oak was preferred over white oak. Frequency-dependent consumption of more common white oak acorns could benefit rarer chestnut during restoration, as squirrels would feed disproportionately on established white oak; however, this management strategy should only be considered following larger-scale and longer-term studies that consider impacts on white oak regeneration. Lack of preference or frequency dependence for chestnut when paired with red oak suggests that negative impacts of fox squirrel consumption on restoration will vary with the relative availability of the two seed types.

In Omsk oblast, the red squirrel Sciurus vulgaris is represented by three chorological groups with different geographic and demographic characteristics. The first group lives in the southern taiga subzone and northern mixed and deciduous forests and represents an indigenous group of S. v. martensi. The second group is formed in the southern subzone of mixed forests as a result of the introduction in 1957–1960 of S. v. exalbidus into the territory of habitation of S. v. martensi and represents a hybrid group different from the aboriginal one in the ratio of native color morphs and population dynamics and density. The third group is formed in the central forest-steppe in artificial pine plantations as a result of the introduction in 1976–1984 of S. v. exalbidus into the free area; it is small with sparse density and a characteristic ratio of color morphs.

Nests play a crucial role in the life history of tree squirrels, and can be a critical component of their biology that enables them to be a successful invasive species. Red-bellied squirrels (Sciurus aureogaster) were introduced to Elliott Key, Florida, in the late 1930s, and spread to nearby islands. Red-bellied squirrels were believed extirpated by Hurricane Andrew in 1992, but were rediscovered on Elliott Key in 2005. In 2006 and 2007, we surveyed for squirrel nests and measured vegetation to evaluate forest characteristics associated with nest-site selection by squirrels, and compared these data to measurements collected at random locations. Squirrels placed nests in large trees with more canopy linkages in mixed-hardwood forest, and the nest trees were in areas with large trees, high tree density and canopy cover, and lower recent hurricane damage. Red-bellied squirrels selected characteristics of nest trees and forest structure in similar ways to individuals in their native range, and to other species of tree squirrels in general. Results from our research allowed land managers to assess possible management actions and provided important information for them to develop an effective management strategy. Park officials are currently working toward complete eradication of the introduced population of red-bellied squirrels from the Florida Keys. We suggest that behaviors of individuals in native ranges may elucidate patterns for individuals introduced to novel environments; however, we also caution that care must be taken in further extrapolation. Our findings emphasize the importance of understanding ecology of introduced species for effective management.

Sciurillus pusillus (E. Geoffroy Saint-Hilaire, 1803) is a sciurid commonly called the Neotropical pygmy squirrel. S. pusillus is an exceptionally small species of tree squirrel that appears pale gray due to a grizzled pattern of light hair tips on the dorsal pelage. Ranging from Amazonian Peru and Brazil northeast to the Guianas with a patchy distribution, S. pusillus is a denizen of the upper canopy of lowland rain forest. This species is listed as “Data Deficient” by the International Union for Conservation of Nature and Natural Resources.

The Eurasian red squirrel (Sciurus vulgaris) is the only naturally occurring tree squirrel throughout its range. We aim at improving current knowledge on its macroparasite fauna, expecting that it will have a poor parasite diversity because in species that have no sympatric congeners parasite richness should be lower than in hosts sharing their range with several closely related species, where host-switching events and lateral transmission are promoted. We examined gastro-intestinal helminth and ectoparasite communities (excluding mites) of, respectively, 147 and 311 red squirrel roadkills collected in four biogeographic regions in Italy and France. As expected, the macroparasite fauna was poor: we found five species of nematodes and some unidentified cestodes, three fleas, two sucking lice and two hard ticks. The helminth community was dominated by a single species, the oxyurid Trypanoxyuris (Rodentoxyuris) sciuri (prevalence, 87 %; mean abundance, 373 ± 65 worms/host). Its abundance varied among seasons and biogeographic regions and increased with body mass in male hosts while decreased in females. The most prevalent ectoparasites were the flea Ceratophyllus (Monopsyllus) sciurorum (28 %), whose presence was affected by season, and the generalist tick Ixodes (Ixodes) ricinus that was found only in France (34 %). All the other helminths and arthropod species were rare, with prevalence below 10 %. However, the first record of Strongyloides robustus, a common nematode of North American Eastern grey squirrels (S. carolinensis), in two red squirrels living in areas where this alien species co-inhabits, deserves further attention, since low parasite richness could result in native red squirrels being particularly vulnerable to parasite spillover.

The only known introduction of a squirrel species into South America is the case of the Asiatic red-bellied tree squirrel Callosciurus erythraeus that was introduced in the Pampas Region of Argentina in 1970. To inform management programmes, we analysed the current distribution, expansion rate, and abundance of the red-bellied squirrel in Argentina, and identified invasion pathways. Apart from the first and main focus of invasion, three other invasion foci have originated as a consequence of intentional releases between 1995 and 2000. The main invasion focus already extends over >1300km2, where estimated density averaged 15indha-1 and numbers of squirrels may reach 100,000 individuals. The area invaded in the other three invasion foci varied between

We predicted that features of the urban environment (uneven habitat from buildings, density of conspecifics and scarcity of dead or dying trees) would lead to different patterns of range overlap for urban and rural fox squirrels Sciurus niger. During 2003–2005 we captured, tracked and calculated seasonal ranges for 60 individuals at an urban site and 45 individuals on a rural site. Differences in range overlaps were best explained by sex, site and season. We observed a greater amount of seasonal range overlap by squirrels on our rural site. Buildings appeared to form the boundary of squirrels' seasonal ranges. By providing clear demarcations of squirrels' ranges, building might have reduced the costs of delineating territories. During the winter, urban squirrels used fewer [urban , 95% confidence interval (CI)=1.0–1.7; rural , 95% CI=2.8–4.2] cavities and anthropogenic shelters, suggesting that cavities might be limited on the urban site and worth the cost of defense. Similar population densities on the sites (urban=1.58 squirrel ha−1, rural=1.45 squirrel ha−1) did not allow us to examine the influence of densities of conspecifics on seasonal range overlaps. The alternative hypothesis, that reduced seasonal range overlaps were a function of range size had little support (female F=1.001, d.f.=82, P=0.130); r males F=2.33, d.f.=118, P=0.320). In summary, squirrels were able to alter their use of space and reduce their range overlap depending on the surrounding environment.

The authors investigated the general activity and nest occupation patterns of fox squirrels in a natural setting using temperature-sensitive data loggers that measure activity as changes in the microenvironment of the animal. Data were obtained from 25 distinct preparations, upon 14 unique squirrels, totaling 1385 recording days. The animals were clearly diurnal, with a predominantly unimodal activity pattern, although individual squirrels occasionally exhibited bimodal patterns, particularly in the spring and summer. Even during the short days of winter (9 hours of light), the squirrels typically left the nest after dawn and returned before dusk, spending only about 7 hours out of the nest each day. Although the duration of the daily active phase did not change with the seasons, the squirrels exited the nest earlier in the day when the days became longer in the summer and exited the nest later in the day when the days became shorter in the winter, thus tracking dawn along the seasons. During the few hours spent outside the nest each day, fox squirrels seemed to spend most of the time sitting or lying. These findings suggest that fox squirrels may have adopted a slow life history strategy that involves long periods of rest on trees and short periods of ground activity each day.

Reintroduction efforts require knowledge of how many animals are needed for successful establishment. Population viability analysis can be used to predict trajectories of introduced populations and tree squirrels provide an ideal model system to investigate this challenge. Conservation action is needed because more than 80% of species of tree squirrels are of precarious conservation status in some portion of their range. We combined data from closely related species of tree squirrels and used VORTEX to determine how many squirrels are needed to successfully establish populations of 6 species (Sciurus aberti, S. carolinensis, S. niger, S. granatensis, S. vulgaris, and Tamiasciurus hudsonicus). We ran multiple simulations to account for betweenpatch differences in breeding success (resource availability) and variation between years in different habitats. In the best-case scenarios, populations could be successfully established with fewer than 35 individuals for all species and as few as 15 for a subset of species. Empirical evidence from introductions of tree squirrels supports our simulation results, with 93% of populations of greater than 10 squirrels surviving more than 50 years. With relatively few individuals needed for establishing new squirrel populations, reintroductions are feasible and useful as a buffer for imperiled species.

Few investigators have considered whether predictors of species occurrence from 1 locality are useful predictors in others, or how regional factors may constrain occurrence. We used landowner questionnaires over 6 regions in Indiana to test the performance of predictors from prior studies of more limited spatial extent. Logistic regression and classification tree models were constructed using data on 577 forest patches supplied by 362 landowners. Consistent with predictions, probability of occurrence of eastern gray squirrels (Sciurus carolinensis) was related positively to forest patch size and percent of forest in the surrounding landscape. Also, probability of occurrence of North American red squirrels (Tamiasciurus hudsonicus) was related positively to the presence of black walnut trees (Juglans nigra) and conifers in forest patches, and negatively to the presence of gray squirrels. Occurrence rates of S. carolinensis increased from north to south, whereas occurrence rates of T. hudsonicus increased from south to north and from west to east. Based on landowner perceptions, abundance of T. hudsonicus was more likely to increase in north and central regions, and to decline in patches with walnuts and at sites with longer periods of observation by landowners. Although less detailed than studies restricted to a particular locality, questionnaire data permit ecologists to test the generality of local findings and to further formulate and refine hypotheses about processes underlying large-scale patterns.

The diverse ecological roles played by different rodent species mean that the loss of some species and superabundance of others could potentially influence a wide range of ecological processes. Hong Kong (22° N, 114° E), with seven million people in a land area of 1100 km2, could be considered a `worst case scenario' for the survival of mammalian diversity. Existing information on rodents in Hong Kong was compiled from previous published and unpublished studies, and additional trapping was conducted at 17 non-urban sites. The rodent fauna of modern Hong Kong consists of eight species of rats and mice (Bandicota indica, Mus caroli, M. musculus, Niviventer fulvescens, Rattus norvegicus, R. rattus, R. tanezumi, R. sikkimensis: Muridae), one porcupine (Hystrix brachyura: Hystricidae), and one recently introduced tree squirrel (Callosciurus erythraeus: Sciuridae). Six of the murids are urban or agricultural commensals, so only the porcupine and two murids, N. fulvescens and R. sikkimensis, are likely survivors of Hong Kong's pre-deforestation native rodent fauna. The two murids co-dominate in forest and shrubland, but can also move through grassland, which has probably enabled their survival through repeated cycles of fragmentation and regrowth. Additional forest rodents that may have inhabited Hong Kong in the past are tentatively identified from information on their recent distributions in the region. One possible ecological consequence of Hong Kong's depleted rodent fauna is a shift in the balance between seed predation and seed dispersal, in favor of the former.

Extant species in human-dominated landscapes differ in their sensitivity to habitat loss and fragmentation, although extinctions induced by environmental alteration reduce variation and result in a surviving subset of species with some degree of ‘resistance’. Here, we test the degree to which variable responses to habitat alteration are (1) essentially an inherent property of a taxon subject to constraints imposed by its geographical range, as suggested by Swihart et al. (2003), (2) a function of the landscape in which a species occurs, or (3) a function of spatial trends occurring on large scales. We used data collected on 33 vertebrate species during 2001–04 across the upper Wabash River basin, Indiana, in 35 square ‘landscapes’, each 23 km2 in size. Six species of forest rodent, six species of grassland rodents, seven species of bats, eight species of aquatic turtles, and six species of amphibians were sampled at 504, 212, 590, 228, and 625 patches, respectively. The fraction of patches of primary habitat (e.g. forests for tree squirrels, wetlands for aquatic turtles) occupied by a target species was used as a response variable. On a basin-wide scale, 47% of variation in proportional occupancy among species could be explained by taxon-specific variables; occupancy rates were related positively to niche breadth and negatively to the proximity of a geographical range boundary. After controlling for species effects, landscape-level occupancy rates varied significantly for 16 of 33 species, with variation partitioned among landscape variables alone (mean = 11% of variation), spatial trend variables alone (26%), and both variable sets jointly (8%). Among landscape variables, percentage forest cover positively affected occupancy rates of three bat species and a tree squirrel. Variation in occupancy rates among landscapes was consistent with large-scale spatial trends for 13 species. Our findings demonstrate the general importance of niche breadth as a predictor of species responses to habitat alteration and highlight the importance of viewing the effects of habitat loss and fragmentation at multiple spatial scales.

Two species of tree squirrel inhabit the Chicago region, the fox (Sciurus niger) and gray (S. carolinien- sis) squirrel. Chicago residents submitted squirrel observations and associated landscape variables via a Website, allowing us to map squirrel distributions. Data were analyzed for patterns of correlation. At a smaller scale, we did a foot survey of fox and gray squirrels in the suburb of Oak Park, replicating an earlier study and comparing results. Gray squirrels were associated with densely populated areas, parks and campuses, fox squirrels with suburban areas. Compared to gray squirrels, fox squirrels were more likely to be observed in areas of high cat density. In the suburb of Oak Park, the current trend seems to be an extension of gray squirrel distribution and a decrease in fox squirrel distribution. Our study provides support for the idea that fox and gray squirrel coexistence is facilitated by a trade-off between managing the cost of predation and foraging efficiency, gray squirrels out-competing fox squirrels in areas of high food and low predator (or pet) density.

A new species of squirrel, Sciurus olsoni, from the late Miocene (Clarendonian) of Nevada, is distinguished from other species of Sciurus by its smaller size and minor differences in the cheek teeth. It is the first Miocene record of the extant genus Sciurus, and the first record of a tree squirrel (tribe Sciurini) in North America between the early Miocene (Arikareean) and the Pleistocene. This late Miocene occurrence in North America suggests that the history of tree squirrels in North America was probably continuous through the Neogene, and the intermittent fossil record is due both to preservation bias and to their never having been abundant as living elements of fossil faunas; they are rare even where they do occur in deposits that are otherwise very richly fossiliferous. The later Tertiary and Pleistocene radiation of tree squirrels may have originated in North America.

The North American red squirrel (Tamiasciurus hudsonicus) has expanded its range into the central hardwoods of the United States in conjunction with increasing forest fragmentation and declining gray squirrel (Sciurus carolinensis) populations. We used translocation experiments and patch occupancy data to test for interspecific differences in mobility and sensitivity to habitat loss and modification by agriculture. We released squirrels in fencerows to test the hypothesis that gray squirrels display inferior mobility relative to red and fox (S. niger) squirrels. Elapsed time to movement from fencerows for 76 individuals increased with distance to forest patches and harvesting of crops. Gray and red squirrels took longer to move from fencerows than fox squirrels, and gray squirrels were less successful at moving from fencerows than fed and fox squirrels. Ecologically scaled landscape indices revealed the degree to which interspecific differences in mobility and individual area requirenients accounted for the occurrence of these species across landscapes. Gray squirrel distribution was constrained both by individual area requirements and dispersal ability. Occurrence of red arid fox squirrels was related to patch size but was unaffected by landscape connectivity.

The retina of the gray squirrel (Sciurus carolinensis) contains rods and cones in a ratio of about 2:3. The spectral mechanisms in this retina were examined in behavioral and electrophysiological experiments. Tests of color vision revealed that this animal has a spectral neutral point at about 500 nm and, thus, dichromatic color vision. Recordings made from single optic nerve fibers and results obtained from an analysis of the flicker photometric electroretinogram (ERG) indicated that vision in the gray squirrel is based on three spectral mechanisms. One of these, presumably rod-based, has peak sensitivity at about 502 nm. The other two mechanisms reflect the presence of two classes of cone having average peak sensitivity of about 444 nm and 543 nm.

Home range patterns of squirrels in the genera Sciurus and Tamiasciurus are reviewed. Emphasis is placed on the need to use analytical techniques which are appropriate to the questions of interest, and certain weaknesses in published studies are outlined. Variation in home range size between different species, populations of the same species and individuals of the same population is discussed in relation to ecological theory and the biology of tree squirrels. Larger species do not necessarily have larger home ranges. There is an inverse relationship between home range size and population density, but its interpretation is not clear in the absence of experimental studies. Differential utilization of space within the home range is considered to be a common pattern, although it is rarely explicitly described in tree squirrel studies. In general, species of the genus Tamiasciurus defend exclusive territories, whilst those of the genus Sciurus do not. Explanations for these patterns are discussed in terms of ‘economic defendability’ and resource heterogeneity. Problems for future study are suggested.