Tree Squirrel Species Research Articles

Activity responses of a mammal community to a 17-year cicada emergence event

Abstract During a limited period in the summer of 2021, 17-year cicada species (Magicicada cassini, M. septendecula, M. septendecim) represented a large pulse of easily accessible food unique to forest ecosystems in the eastern United States. Using trail cameras and acoustic recorders, we tested whether the activity levels of 8 mammal species in northwestern Indiana shifted in response to spatial and temporal variation in cicada densities from 18 May to 20 June 2021. Cicada densities varied temporally and spatially across all study sites. Most mammal species with sufficient data showed no response to cicada emergence, including 2 tree squirrel species, Peromyscus mice, Eastern Chipmunks (Tamias striatus), and 2 species of bats. Raccoons (Procyon lotor), likely cicada predators, showed a quadratic or more complex activity response to cicada abundance, indicating a potential saturation point at densities near 1 cicada per m2. Surprisingly, White-tailed Deer (Odocoileus virginianus) activity decreased to almost 0 at the same cicada densities when we expected no change in activity. While size or accessibility may exclude cicadas as prey for small and volant mammals, our results suggest predation and satiation by Raccoons. In contrast, deer may be avoiding areas of cicada abundance due to other stimuli, such as high noise output, which may decrease their ability to detect predators.

Predation risk in tree squirrels: implications of the presence of free‐ranging dogs

AbstractSmall mammals show variations in activity patterns due to the use of resources and the risk of predation. However, in the case of tree squirrel species, the factors that affect their activity patterns are poorly studied. We used camera trapping to investigate the activity patterns of three different squirrel species of the genus Sciurus, two species of squirrel (Sciurus aureogaster and S. oculatus) from Mexico and one from the Iberian Peninsula (S. vulgaris). In addition, we compared their activity patterns with the potential predator community and their most important predators (Mexico: gray fox Urocyon cinereoargenteus, ringtail Bassariscus astutus, Opossum Didelphis virginiana; Spain: red fox Vulpes vulpes, pine and stone marten Martes spp.), and with feral and free‐ranging dogs (Canis lupus familiaris). We evaluated the predation risk by the carnivore community on the squirrels when they descend to the ground by studying their temporal overlap and observing if the squirrels have different activity patterns adjusted to the carnivore community in each study area. The results showed that the three species of squirrels consistently descended to the ground during the day, showing a variable maximum peak of activity between 8:00 and 12:00 h. Temporal overlap of activity patterns of the three species with the carnivore community was low (Δ = 0.12–0.36), same as with the main predators (Mexico: gray fox Δ = 0.14–0.21, ringtail Δ = 0.08–0.09, opossum Δ = 0.06–0.07; Spain: red fox Δ = 0.39, martens Δ = 0.22). However, temporal overlap of activity patterns with the domestic dog was moderate‐high in the three squirrel species (Mexico Δ = 0.55–0.88, Spain Δ = 0.79). These results show that the species of the genus Sciurus have adjusted their activity patterns of ground use to reduce predation risk by wild predators but not with feral and free‐ranging dogs, something which can pose a serious conservation problem for these species.

Prevalence and location of survivable skeletal injuries in two North American tree squirrels (Sciurus)

Abstract Skeletal injuries, especially broken bones, diminish physical mobility of animals, and they may affect an individual’s ability to obtain food and to evade predators. We quantified and compared healed fractures in two sympatric species of tree squirrels (Sciurus niger Linnaeus, 1758 and S. carolinensis Gmelin, 1788) that differ in body size (mass) and locomotor mode. We assessed the number and location of healed fractures in two urban populations of S. carolinensis and in individuals of both species from one rural location. We found a higher-than-expected proportion of healed fractures in older animals of both species. However, we detected no deviations from expected in the number of healed fractures between the two species or between sexes within a species. Urban populations of S. carolinensis exhibited significantly higher-than-expected proportions of healed fractures, and they were approximately 4.5 times more likely to have a healed injury as compared to rural S. carolinensis. Our findings suggest that S. carolinensis in urban populations experience a higher rate of injury and/or a higher rate of survival after injury than those in rural populations.

Reference intervals for hematological variables in wild Eastern grey squirrels (Sciurus carolinensis)

The eastern grey squirrel (Sciurus carolinensis) is a North American tree squirrel species which has been introduced to several countries outside its native range. We made use of squirrels culled in Italy within control activities to establish hematological reference intervals for this invasive species, with the aim to broaden the current knowledge about its physiology. Blood from 104 individuals was analysed through a laser analyser. Manual leukocyte differential counts on blood films from a subset of 77 animals were used for validation of the automated counts, resulting in a fairly good agreement between the two methods for all variables excluding monocytes. Reference intervals and the 90% confidence interval of their limits were estimated for 19 hematological variables, partitioning by sex when statistically significant differences were detected. For most variables, our results were comparable with the few data available on the grey squirrel and on related species. An exception was represented by the hematocrit and mean corpuscular volume which were higher than values reported by other authors, and by the mean corpuscular hemoglobin concentration, which was instead lower. This study gathered valuable reference information for studies aimed at disclosing the mechanisms underlying grey squirrels’ invasiveness and for future research on tree squirrels’ physiology.

Timing of Resource Availability Drives Divergent Social Systems and Home Range Dynamics in Ecologically Similar Tree Squirrels

Intraspecific variation in home range size has important implications for the distribution of animals across landscapes and the spatial structuring of population, community and ecosystem processes. Among species of similar trophic guild and body mass, differences in home range size can reflect extrinsic variables that exert divergent selective forces upon spacing behavior and social organization. We tested predictions about how resource availability and timing influence social system, home range size and territoriality in two tree squirrel species of similar size and ecological niches but that differ in foraging strategy and social organization. We estimated home range size and intraspecific home range core overlap in the Mt. Graham red squirrel (Tamiasciurus fremonti grahamensis; Arizona USA; MGRS) and the Eurasian red squirrel (Sciurus vulgaris; Alps, Italy; ERS) as functions of species, sex, season, and individual’s body mass. However, body mass did not explain differences found between the two species. We found MGRS home ranges being 3 times smaller with higher core area exclusivity compared to ERS in all seasons. In fact, territorial MGRS evolved in a system of brief resource pulses and are larder hoarders, whereas ERS experience prolonged resource availability and are non-territorial. Only male MGRSs increased their home range during the breeding season, reflecting interspecific differences in social organization and mating behavior. Male ERS home ranges always overlap with several females to enhance mating success, while male and female MGRS maintain nearly exclusive territories throughout the year. Only during spring and summer males temporarily leave their food-based territory to increase mating opportunities with neighboring estrus females. Home range comparisons between ecologically similar species emphasized the importance of divergent extrinsic factors in shaping variability in body size – home range size scaling relationships. Timing in resource availability influenced the social structure and space use in tree squirrels of similar body size, highlighting how the coevolution of arboreal squirrels with conifer tree species has shaped their natural history.

Comparison of cranial and body morphology of tree squirrels (<i>Helioscurius rufobranchium</i>) in selected locations of rainforest in Nigeria

This study examined the differences in cranial morphology of tree squirrel species (Heliosciuru srufobranchium) from four different locations in rainforest part of Nigeria. Locally fabricated live traps made of wire-mesh and steel were used to capture the squirrels. Trapped tree squirrels were immediately transferred to the laboratory in cages, where they were euthanized by placement in a bell-jar containing chloroform-soaked cotton wool. Individuals from two locations (33 from Ile Ife and 49 from Emure Ekiti) were then preliminarily identified to the generic level, using an identification key. Eighty-two (82) skulls were prepared from them, using Long Island Natural History Museum Guide. The sexes of the specimens were determined by visual inspection of the external genitalia. Twenty-seven (27) cranial and six (6) external body parameters were measured using digital Vernier caliper. One-way analysis of variance at p<0.05 was used to determine the difference in measured body parameters and Principal Component Analysis was used to differentiate the measured skull parameters. The results showed that the body parameters; head body length, tail length, tail body length, ear length, hind foot length and body weight measured were slightly different from one location to another. Also, the cranial measurements showed some similarities and differences between the two locations (Ile Ife and Emure Ekiti). In conclusion, the cranial measurements of the tree squirrels from the two locations (Ile Ife and Emure Ekiti) showed slight differences despite the fact that the tree squirrels are from the same genus (H. rufobranchium).
 Keywords: Heliosciurus rufobranchium; rainforest; tree squirrel; cranial; morphometric

Habitat-based isolating barriers are not strong in the speciation of ecologically divergent squirrels (Tamiasciurus douglasii and T. hudsonicus)

Adaptations to different environments between closely related species can be important drivers of reproductive isolation during speciation due to either habitat isolation between species or reduced fitness in hybrids that possess suboptimal adaptations. Hybrid zones are useful natural arenas to explore how ecologically divergent species compete for habitat in sympatry and how possible differences in their habitat use may contribute to the speciation process. We investigated habitat selection by sister species of tree squirrels, the Douglas squirrel and the red squirrel, that have evolved in different forest types in allopatry and hybridize in a transitional forest. We first used genome-wide SNP data and admixture analyses to classify individuals into parental or hybrid classes. Next, we estimated home ranges with radio telemetry data and then used a novel ground-based lidar system to measure forest canopy structure of squirrel home ranges, midden sites, and marginally used forest habitat. We found hybrids consisting of multiple hybrid classes were intermixed with both parental species in the same forest with varying canopy structure complexity. On average, Douglas squirrels utilized forests with slightly greater structural complexity than either red squirrels or hybrids, while marginally used forests were the least structurally complex. Interestingly, hybrid squirrels were not relegated to marginal habitat and were successful in mating among each other and with both parental species. As such, our study suggests that prezygotic-ecological isolation and postzygotic-hybrid infertility, and postzygotic ecological inviability of hybrids are not strong barriers in the speciation process between Douglas squirrels and red squirrels. Closely related species that become geographically divided often encounter different environments and thus evolve different adaptations. Sometimes, these species meet again and produce hybrids. Hybrids often have lower fitness due to their inferior adaptations. We studied a pair of closely related squirrels that evolved in different environments and meet and produce hybrids in a secondary contact zone. Despite these species evolving in allopatry in very different forest types, they do not select different forest characteristics while in sympatry in the hybrid zone. Furthermore, hybrids do not show major differences in types of habitats that they choose and are capable of defending territories and reproducing among each other and with both parental species. In summary, prezygotic and postzygotic isolating mechanisms associated with habitat selection do not appear to have an important role in promoting species divergence.

Comparison of Cranial and External Morphology of Tree Squirrels (Funiscurus leucogenys) in Selected Locations of Rainforest in Nigeria

This study looked at the differences in cranial morphology of tree squirrel species (F. leucogenys) from four different locations in Rainforest part of Nigeria. The squirrels were captured through the use of locally fabricated live traps made of wire-mesh and steel. Trapped specimens were immediately transferred to the laboratory in captivity cages, where they were euthanized in a bell-jar containing chloroform-soaked cotton wool. Specimens were then preliminarily identified to the generic level, using an identification key. The skull of 131 tree squirrels were prepared using Long Island Natural History Museum guide and the sex of the specimens was determined by visual inspection of the external genitalia. The skull and other body parameters were measured using digital venier caliper. The results showed that the body parameters (HBL, TL, TBL, EL, HFL and BW) measured were slightly different from one location to another. Also, the cranial measure showed some similarities among some locations (Ile-Ife, Emure-Ekiti and Ado-Ekiti), while measurement on squirrels from Sekona was different from other three locations. In conclusion, the cranial measurements of the tree squirrels shows there was no new species of F. leucogeny from the sampled locations.

Comparative analysis of microbiota along the length of the gastrointestinal tract of two tree squirrel species (Sciurus aberti and S. niger) living in sympatry.

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.

Geographical variation in Eurasian red squirrel (Sciurus vulgaris L., 1758) mandibles and the issue of subspecies-level organization: a failure of history?

AbstractSciurus vulgaris is a widespread, highly polytypic tree squirrel species, under which a large number of subspecies have been described. This study tests the robustness of the current subspecific classification by using geometric morphometrics to quantify morphological variation in mandible shape, along with canonical variates analysis to test hypotheses of morphological distinctiveness. Patterns of mandible allometry were examined in eight out of 16 currently recognized subspecies. The significance of the discriminate functions was tested statistically, and the iterative jackknife procedure was applied to evaluate stability of the subspecies-specific discriminant functions. Applying criteria that focus on shape diagnosability, rather than mean group differences, indicates that most regional subspecific groupings show intergradations and continuity in mandible shape and size and that allometric effects on mandible shape are negligible. Evidence of a distinct subspecies confined to the Iberian Peninsula (Sciurus vulgaris infuscatus) and a discrete group originating from an extinct, 19th century population in Dorset, UK were identified based on these mandibular data. All other regional subspecific groupings were not diagnosably different. These results suggest that most red squirrel subspecies might represent non-diagnosable morphological variants whose taxonomic validity seems doubtful. More generally, our results highlight the importance of applying objective, quantitative and reproducible criteria to the issue of subspecies delimitation.

Multiple origins of melanism in two species of North American tree squirrel (Sciurus)

BackgroundWhile 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”).ResultsWe 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.ConclusionsThe 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.

Cranial and External Morphology of Male and Female Orange Headed Tree Squirrels (Funisciurus leucogenys) in Selected Locations of Savannah Forest in Nigeria

This study examined the differences in cranial and external morphology of male and female tree squirrel species (Funisciurus leucogenys) from three different locations in Savannah vegetation zone of Nigeria. The tree squirrels were collected from contracted local hunters which identify the tree squirrel. After collection and identification to the generic level, they were transferred to the laboratory in absolute ethanol. About 183 skulls were prepared (58 male and 125 female), the skull and other body parameters were measured using digital venire calliper. The results showed that the body parameters (HBL, TL, TBL, EL, HFL, and BW) of the female specimen measured were different from male and the body parameters of the specimen from one location were slightly different from another. Also, the cranial measure showed some similarities and slight differences between male and female specimen among the locations (Asejire, Ilorin, and Ogbomosho). In conclusion, the cranial and body morphology parameters of male and female tree squirrels from the three locations (Asejire, Ilorin, and Ogbomosho) showed that despite that the tree squirrels were from different locations, they were of the same genus (F. leucogeny), which indicated that locations might not have an effect on the specimen.

Effect of Wildfire on the Occurrence of Three Squirrel Species in a Dry Dipterocarp Forest in Northeastern Thailand

Abstract. Wildfires occur almost every year at the end of the dry season in some dry dipterocarp forests (or dry deciduous forests) of northeastern Thailand. This study assessed the effects of a wildfire on the occurrence of variable squirrels (Callosciurus finlaysonii), gray-bellied squirrels (C. caniceps), and Indochinese ground squirrels (Menetes berdmorei). Route census surveys before and after the wildfire revealed that the frequency of occurrence of the two tree squirrels (Callosciurus spp.) did not change, whereas that of the Indochinese ground squirrel decreased. The wildfire burned bushes and grasses but did not destroy the trees, leaving the food and resting sites for the tree squirrel species intact. Therefore, wildfires in this area may have no clear effects on tree squirrel species, but negative ones on ground squirrels. The probable reasons for these findings may be the nature and extent of the wildfire, as well as the space utilization of the squirrel species.

Distribution of the Eastern Gray Squirrel (Sciurus carolinensis) within California as of 2015

The goals of this study were to map the distribution of the invasive eastern gray squirrel, Sciurus carolinensis, in California as of 2015 and to assess range expansion since the first documented sightings within the state. Range maps exist, but the last update by the California Department of Fish and Wildlife was in 2007. An assessment of the rate of range expansion over time has not been conducted, but comparisons between the locations of initial sightings and the current distribution are included. Location data were obtained from museum specimens, wildlife rehabilitation centers, a roadkill database, and research-grade citizen observations. Range maps were produced with ArcGIS software. Populations of eastern gray squirrels are currently concentrated around Sacramento and Davis, the western side of San Francisco Bay, within as well as north and east of Santa Cruz, within Monterey, north of the Golden Gate Bridge through Marin County as well as around Santa Rosa, and around the Bellota/Stockton area. Isolated populations on the eastern side of San Francisco Bay occur around Berkeley, Hayward, and Pleasanton. Observations extend into the foothills of the Sierra Nevada Mountain Range from north of the American River to south of the San Antonio River. We suggest that the eastern gray squirrel might become more damaging to the two native diurnal species of tree squirrels in California, Sciurus griseus and Tamiasciurus douglasii, than the introduced eastern fox squirrel (Sciurus niger).

Native and introduced squirrels in Italy host different Cryptosporidium spp.

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.

New endemic mammal species for Europe: Sciurus meridionalis (Rodentia, Sciuridae)

Combining genetic, morphological and geographical data, we re-evaluate Sciurus meridionalis , Lucifero 1907 as a tree squirrel species. The species, previously considered a subspecies of the Eurasian red squirrel, Sciurus vulgaris , is endemic to South Italy with a disjunct distribution with respect to S. vulgaris . The new species has a typical, monomorphic coat colour characterized by a white ventral fur and a very dark-brown to blackish fur on the back, sides and tail. Specimens of S. meridionalis have a larger hind foot length and weigh about 35% more than live-caught S. vulgaris from northern Italy. S. meridionalis is larger than S. vulgaris specimens from three other regions in Italy for mandible length, skull width and skull (condylobasal) length, and principal component scores indicate significant shape differences of specimens from the Calabria population ( S. meridionalis ) compared to all other specimens ( S. vulgaris ). These morphological differences are further supported by genetic evidence at three mitochondrial markers (D-loop, cytochrome b and the DNA barcoding region COI) using the widest molecular dataset ever assembled for Sciurus vulgaris and S. meridionalis . All the investigated markers revealed exclusive haplotypes for S. meridionalis well separated from those of S. vulgaris and previously published results based on nuclear markers further support our taxonomic hypothesis. We suggest Calabrian black squirrel as common name for this new taxon.

Impact of Global Climate Change on Pollinator Diversity and Conservation: Current Issues and Future Challenges

Over 75% of the major world crops and 80% of all flowering plant species rely on animal pollinators. Of the hundred or so animal-pollinated crops which make up most of the world's food supply, 15% are pollinated by domestic bees, while at least 80% are pollinated by wild bee species and other wildlife. Most of the 25, 000 to 30, 000 species of bees are effective pollinators, and together with moths, flies, wasps, beetles and butterflies, make up the majority of pollinating species. Vertebrate pollinators include bats, non-flying mammals (several species of monkey, rodents, lemur and tree squirrels etc.) and birds (humming birds, sun birds, honey creepers and some parrot species). Current understanding of pollination process shows that, while an interesting specialized relationship exist between plants and their pollinators, healthy pollination services are best ensured by an abundant diversity of pollinators. Thus, pollinators are essential for diet diversity, biodiversity, and maintenance of natural resources. Pollinators which evolved over million of years, are eroding at a fast rate from the globe. During the past few years, many pollinators especially honey bees have been dying across the globe in unprecedented number and, no one has so far been able to prove beyond a reasonable doubt what the causes may have been. The economic implications of these deaths are immediate because honey bees are integral to the pollination of tens of millions of dollars of cash crops in the world. Despite much of the world's agriculture relying on pollination by honeybees, especially European honeybees, their number across the globe has also declined. Many other pollinators such as digger bees, sweat bees, alkali bees, squash bees, leafcutter bees, carpenter bees, mason bees, and shaggy fuzzy foot bees could also be on decline, but data providing unambiguous documentation of trends are simply not available. Threats to pollinators and the services they provide are perceived to be increasing around the world and are mainly man-made in origin. Climate change could be a major factor in weakening the bees and has affected the pollination of crops in many agricultural areas. An attempt has been made to know the causes behind the decline of pollinators, especially in relation to climate change, their conservation and management and impact of declining pollinator population on horticulture in the changed global scenario.

How do Neotropical pygmy squirrels (Sciurillus pusillus) use seasonally flooded forests in the Peruvian Amazon?

Tree squirrels are important components of ecosystems but to understand their role, we must learn how squirrels select and use habitat. Tree squirrel species richness is highest in the tropics and, according to the International Union for Conservation of Nature, is also where the greatest number of data deficient species occurs. The Neotropical pygmy squirrel (Sciurillus pusillus) is one of these species. In 2009 and 2010, we conducted distance sampling to estimate population density, we measured vegetation variables to investigate forest characteristics that influence habitat selection at 3 different scales, and conducted observations to obtain knowledge about activity patterns and behavior of Neotropical pygmy squirrels in igapo forest in the Peruvian Amazon. Density of squirrels was 0.10 and 0.14 individuals/ha, respectively, for each year. Squirrel activity peaked at 0800 h, individuals were found mainly in the canopy and never on the ground, and frequency of squirrel behaviors differed by time and st...

Food Selection of Coexisting Western Gray Squirrels and Eastern Fox Squirrels in a Native California Botanic Garden in Claremont, California

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

Landscape-level assessment of Abert's Squirrel and Red Squirrel in Mixed Conifer Forest

Abstract We examined feeding sign of Abert's squirrels (Sciurus aberti) and red squirrels (Tamiasciurus hudsonicus) each spring 2005–2009 in mixed conifer forests in northern Arizona, USA. We used high-resolution aerial photographs to assess vegetation characteristics where feeding sign surveys were conducted and analyzed the association of feeding sign frequency to vegetation characteristics to compare and contrast species habitat use. At the landscape level, we found considerable overlap in characteristics of forests used by the two species of native tree squirrels. Red squirrels used denser forests with fewer and smaller gaps than do Abert's squirrels, and Abert's squirrels used more ponderosa pine (Pinus ponderosa) than do red squirrels.