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This comprehensive book, the first text on this species, has an extensive literature review and list of references, and beautiful full-color photography illustrating the squirrels and their magnificent ponderosa habitat. Sylvester Allred reveals the history of the Kaibab squirrel, including brief biographies of the early naturalists who first described them, and descriptions of fossils and other remains that reveal the evolutionary history of these unique creatures. Throughout the book more than forty research topics for future exploration are identified.

We developed an exercise for a university-level ecology class that teaches hypothesis testing by examining acorn preferences and caching behavior of tree squirrels (Sciurus spp.). This exercise is easily modified to teach concepts of behavioral ecology for earlier grades, particularly high school, and provides students with a theoretical basis for examining commonly observed squirrel behavior. Students gain experience in testing hypotheses and revising predictions. They evaluate how well predictions of competing hypotheses are supported by statistically analyzing and interpreting class data using t-tests and chi-square tests.

Understanding how biodiversity responds to urbanization is challenging, due in part to the single-city focus of most urban ecological research. Here, we delineate continent-scale patterns in urban species assemblages by leveraging data from a multi-city camera trap survey and quantify how differences in greenspace availability and average housing density among 10 North American cities relate to the distribution of eight widespread North American mammals. To do so, we deployed camera traps at 569 sites across these ten cities between 18 June and 14 August. Most data came from 2017, though some cities contributed 2016 or 2018 data if it was available. We found that the magnitude and direction of most species’ responses to urbanization within a city were associated with landscape-scale differences among cities. For example, eastern gray squirrel (Sciurus carolinensis), fox squirrel (Sciurus niger), and red fox (Vulpes vulpes) responses to urbanization changed from negative to positive once the proportion of green space within a city was >∼20%. Likewise, raccoon (Procyon lotor) and Virginia opossum (Didelphis virginiana) responses to urbanization changed from positive to negative once the average housing density of a city exceeded about 700 housing units/km². We also found that local species richness within cities consistently declined with urbanization in only the more densely developed cities (>∼700 housing units/km²). Given our results, it may therefore be possible to design cities to better support biodiversity and reduce the negative influence of urbanization on wildlife by, for example, increasing the amount of green space within a city. Additionally, it may be most important for densely populated cities to find innovative solutions to bolster wildlife resilience because they were the most likely to observe diversity losses of common urban species.

Invasive species are a major threat to biodiversity worldwide and tree squirrels (Sciuridae) are among the most successful mammalian invaders. Two tree squirrels native to the eastern United States, the eastern grey squirrel (Sciurus carolinensis) and eastern fox squirrel (Sciurus niger), have been repeatedly introduced into the western United States over the past century. In that time, the non-native species have expanded their ranges extensively and have negatively impacted the only native species of large tree squirrel in the western United States, the western grey squirrel (Sciurus griseus). While numerous studies have documented the impacts of these invasions on S. griseus, few have assessed the potential for future expansion and none have evaluated all three squirrel species simultaneously. In this study, we address: whether the predicted distributions derived from observations in the western states differ from those derived from the native eastern distribution; to what extent do the predicted distributions overlap with the native S. griseus; what role does urbanization play in invasion potential of the introduced squirrels. We use citizen science data from the iNaturalist database to model the species distributions in the western United States for all three Sciurus species. We generated models based on occurrences in the squirrels’ native ranges, compared to models generated from their introduced ranges, and evaluated current and predicted conflict zones. We determined that the greatest potential conflict with the native squirrel is currently in areas adjacent to regions of high human footprint. As human development expands, the invasive squirrels are likely to expand into previously inaccessible areas, increasing conflict with and potentially displacing the native western grey squirrel.

Squirrels on North American college and university campuses have been the subject of much animated conversation in informal venues, but a systematic assessment of their distribution across this habitat type has not been undertaken until now. We collected reports of squirrel species' presence and absence from faculty experts at 536 campuses in Canada and the continental United States, and found that squirrels are nearly ubiquitous on campuses (95% had at least one species, and 40% had three or more), but that only a select few species are common campus residents. Foremost among these is the eastern gray squirrel (Sciurus carolinensis—on 62% of surveyed campuses), followed by the eastern fox squirrel (Sciurus niger), eastern chipmunk (Tamias striatus), North American red squirrel (Tamiasciurus hudsonicus), and woodchuck (Marmota monax). Eastern gray and fox squirrels partition campuses with one another, both in their shared native/core range and on the West Coast. While these invasive eastern species are present on campuses on the West Coast, notably, contingency analysis did not provide evidence that they are the primary factor discouraging western gray squirrels (Sciurus griseus) from using these habitats. The inventory and analyses presented here can provide a basis for longitudinal studies both within and across campuses and may be productively combined with initiatives that involve students in research.

Since its introduction from the United States in 1876, the invasive North American Eastern grey squirrel (Sciurus carolinensis) has contributed to the decline of the native Eurasian red squirrel (Sciurus vulgaris) in Britain. The aim of this study was to assess the overall impact of repeated control efforts carried out between 2011 and 2020 on the genetic diversity of the grey squirrel population in north Wales. This information can be used to inform future adaptive management plans, increasing the success of invasive species control efforts and enhancing red squirrel conservation efforts. Using a combination of mitochondrial DNA (mtDNA) and microsatellite DNA analysis, we found high genetic diversity in both marker types, with six diverse mtDNA haplotypes found and relatively high levels of nuclear genetic diversity, even after repeated culling efforts. We also found that repeated introductions from multiple locations in North America have generated a genetically diverse population in Britain today, compounding the management of this invasive species. Our results suggest that ongoing grey squirrel control efforts may not adequately reduce genetic diversity to a level where it contributes to a long-term population decline, and highlights the need to gather all available information, including historical and contemporary, to effectively create a plan for control efforts of invasive species.

Background While our understanding of the genetic basis of convergent evolution has improved there are still many uncertainties. Here we investigate the repeated evolution of dark colouration (melanism) in eastern fox squirrels ( Sciurus niger; hereafter “fox squirrels”) and eastern gray squirrels ( S. carolinensis; hereafter “gray squirrels”). Results We show that convergent evolution of melanism has arisen by independent genetic mechanisms in two populations of the fox squirrel. In a western population, melanism is associated with a 24 bp deletion in the melanocortin-1-receptor gene ( MC1RΔ24 allele), whereas in a south-eastern population, melanism is associated with a point substitution in the agouti signalling protein gene causing a Gly121Cys mutation . The MC1R∆24 allele is also associated with melanism in gray squirrels, and, remarkably, all the MC1R∆24 haplotypes are identical in the two species. Evolutionary analyses show that the MC1R∆24 haplotype is more closely related to other MC1R haplotypes in the fox squirrel than in the gray squirrel. Modelling supports the possibility of gene flow between the two species. Conclusions The presence of the MC1R∆24 allele and melanism in gray squirrels is likely due to introgression from fox squirrels, although we cannot completely rule out alternative hypotheses including introgression from gray squirrels to fox squirrels, or an ancestral polymorphism. Convergent melanism in these two species of tree squirrels has evolved by at least two and probably three different evolutionary routes.

Introduced hosts populations may benefit of an \"enemy release\" through impoverishment of parasite communities made of both few imported species and few acquired local ones. Moreover, closely related competing native hosts can be affected by acquiring introduced taxa (spillover) and by increased transmission risk of native parasites (spillback). We determined the macroparasite fauna of invasive grey squirrels (Sciurus carolinensis) in Italy to detect any diversity loss, introduction of novel parasites or acquisition of local ones, and analysed variation in parasite burdens to identify factors that may increase transmission risk for native red squirrels (S. vulgaris). Based on 277 grey squirrels sampled from 7 populations characterised by different time scales in introduction events, we identified 7 gastro-intestinal helminths and 4 parasite arthropods. Parasite richness is lower than in grey squirrel's native range and independent from introduction time lags. The most common parasites are Nearctic nematodes Strongyloides robustus (prevalence: 56.6%) and Trichostrongylus calcaratus (6.5%), red squirrel flea Ceratophyllus sciurorum (26.0%) and Holarctic sucking louse Neohaematopinus sciuri (17.7%). All other parasites are European or cosmopolitan species with prevalence below 5%. S. robustus abundance is positively affected by host density and body mass, C. sciurorum abundance increases with host density and varies with seasons. Overall, we show that grey squirrels in Italy may benefit of an enemy release, and both spillback and spillover processes towards native red squirrels may occur.

1. Invasive alien species can cause extinction of native species through processes including predation, interspecific competition for resources or disease-mediated competition. Increases in stress hormones in vertebrates may be associated with these processes and contribute to the decline in survival or reproduction of the native species. 2. Eurasian red squirrels (Sdurus vulgaris) have gone extinct across much of the British Isles and parts of Northern Italy following the introduction of North American invasive grey squirrels (Sdurus carolinensis). We extracted glucocorticoid metabolites from faecal samples to measure whether the presence of the invasive species causes an increase in physiological stress in individuals of the native species. 3. We show that native red squirrels in seven sites where they co-occurred with invasive grey squirrels had glucocorticoid concentrations that were three times higher than those in five sites without the invasive species. Moreover, in a longitudinal study, stress hormones in native red squirrels increased after colonisation by grey squirrels. When we experimentally reduced the abundance of the invasive grey squirrels, the concentration of faecal glucocorticoid metabolites in co-occurring red squirrels decreased significantly between pre- and postremoval periods. 4. Hence, we found that the invasive species acts as a stressor which significantly increases the concentrations of glucocorticoids in the native species. 5. Given that sustained elevations in glucocorticoids could reduce body growth and reproductive rate, our results are consistent with previous studies where the cooccurrence of the invasive grey squirrel was associated with smaller size and lower reproductive output in red squirrels.

Fluorescence of visible wavelengths under ultraviolet (UV) light has been previously detected in a wide range of birds, reptiles, and amphibians and a few marsupial mammals. Here, we report the discovery of vivid UV fluorescence of the pelage in Glaucomys, the New World flying squirrels. Fluorescence in varying intensities of pink was observed in females and males of all extant species (G. oregonensis, G. sabrinus, and G. volans) across all sampled geographic areas in North and Central America and a temporal range of 130 years. We observed fluorescence in museum specimens (n = 109) and wild individuals (n = 5) on both dorsal and ventral surfaces. Museum specimens of three co-occurring, diurnal sciurid species (Sciurus carolinensis, S. niger, and Tamiasciurus hudsonicus) were also examined but did not fluoresce. The ecological significance of this trait in the nocturnal–crepuscular flying squirrels warrants further investigation.