Tree Squirrels Research Articles

Impact of forest management on the communication distance of an endangered tree squirrel

Impact of forest management on the communication distance of an endangered tree squirrel

Lost in synonymy: Integrative species delimitation reveals two unrecognized species of Southern Asian tree squirrels (Rodentia: Sciuridae: Callosciurinae)

Abstract We present a comprehensive integrative taxonomic review of Callosciurus caniceps and Tamiops mcclellandii as they are currently defined. This review combines published molecular evidence, craniodental morphometrics, pelage and bacular variation, evaluations of potential hybrid zones using museum specimens and citizen science photographs, and, for C. caniceps, bioacoustic evidence. Our findings lead to the recognition of two species that had been lost in synonymy and highlight future perspectives on species delimitation in Sciuridae. By comparing phenotypic differentiation across climatic and vegetation transitions and contextualizing our results with the evolutionary history of our study systems, we provide insights into distribution, ecogeographical patterns, and speciation drivers in Southeast Asian vertebrates.

Comparative selective pressure analysis on mitochondrial protein-coding genes in flying squirrels (Pteromyini) and tree squirrels (Sciurini)

Different animal groups with varying locomotion modes may have unique energy requirements. Mitochondria produce adenosine triphosphate (ATP) and reactive oxygen species via oxidative phosphorylation to support organisms energy requirements. The tribes Pteromyini (flying squirrels) and Sciurini (tree squirrels), two closely related taxa within the family Sciuridae, exhibit distinct locomotion modes, energy requirements, and likely face different selective pressures on mitochondrial protein-coding genes (PCGs). We analysed 13 mitochondrial genome sequences from species belonging to the tribe Pteromyini and 117 from species belonging to the tribe Sciurini. Phylogenetic analysis revealed Pteromyini and Sciurini formed a sister relationship within the family Sciuridae. Among the 13 PCGs, ATP8 exhibited the highest dN/dS values, while COX1 showed the lowest. The background selection ratio (ω2) values for six genes (ND1, ND2, ND4, ATP6, ND5, and COX3) in Pteromyini were lower than the foreground selection ratio (ω0) values observed in Sciurini. A RELAX analysis revealed that CYTB, ND4, ATP6, and COX3 genes experienced intensified in selection strength. BUSTED analysis identified stronger signatures of diversifying selection in CYTB and ATP6, highlighting amino acid changes. MEME identified episodic diversifying selection at specific sites among eight PCGs. These findings revealed distinct selective pressures on PCGs in flying and tree squirrels.

Occurrence of Fox Squirrels Influenced by Fine-Scale Landscape Characteristics on a College Campus.

Urbanization and urban sprawl generally degrade and diminish wildlife habitat, threatening to extirpate local populations. However, certain synanthropic species (e.g., coyotes, white-tailed deer, and squirrels) are able to persist in urban environments and may even occur at greater densities than they do in their natural habitats. Eastern fox squirrels (Sciurus niger) are large tree squirrels that are known to be present in greater densities within urban areas. To determine how landscape characteristics may affect fox squirrel presence, we conducted line-transect surveys along sidewalks on the Texas A&M University-College Station campus to record presence of fox squirrels and nearest tree species. We calculated Jacobs' index of selectivity (D) for use of trees by fox squirrels along the transects. Squirrel density was calculated for all transects and modeled using linear regression with environmental (e.g., tree density) and survey (e.g., transect distance) variables. Fox squirrels preferred only a small number of the available tree species, primarily Quercus and Ulmus species. Observed fox squirrel density significantly increased with time of day, temperature, density of oaks (Quercus spp.), and density of all trees, and decreased with distance and area of the transect. These results suggest that even when urban areas contain suitable habitat, use of urban environments by wildlife is still highly selective and dependent on specific habitat requirements.

ENut: A Sensing System to Measure the Acquisition of Foraging Proficiency in Wild Tree Squirrels

<i>eNut</i>: A Sensing System to Measure the Acquisition of Foraging Proficiency in Wild Tree Squirrels

Patterns in tree squirrel co-occurrence vary with responses to local land cover in US cities

Patterns in tree squirrel co-occurrence vary with responses to local land cover in US cities

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.

Histomorphological Investigation of the Eye of the Tree Squirrel: A Preliminary Study

Abstract Squirrels are diurnal rodents with high visual acuity including unique properties well-suited for their natural environment. This study was conducted to explore some ocular microscopic features of tree-harbouring squirrels in the University of Ibadan, Ibadan, Nigeria. Two male squirrels were cage-trapped within the University premises. Light microscopic analysis was carried on paraffin-embedded eye samples harvested from the animals. The densely compacted stromal fibres, 351 ± 52.5 µm thick, formed the thickest part of the cornea, and the basement membrane of the corneal epithelium, 63.8 ± 13.0 µm thick, was notably positive with Periodic Acid Schiff (PAS) stain. Strong pigmentation was present at the choroid as well as the iridal and ciliary epithelia. The multiple layering of the retinal structure exhibited densely packed ganglion cells at the ganglion cell layer which together with the nerve fibre layer was observed to be thinnest at the more peripheral portion but becomes thicker towards the optic disc. Strongly positive glia fibrillary acidic protein (GFAP+) cells with their abundant fibrous processes were demonstrated immunohistochemically at the retinal nerve fibre layer and the optic nerve. Histological features of the retinal cellular components of the tree squirrels investigated has thus highlighted the structural adaptation of these animal species to their environmental arboreal habitat and diurnal lifestyle. Findings from this study, while further noted to be similar to that in human, showed that African tree squirrels represent promising rodent model for human retinal/ocular research.

The Genetic Basis of Melanism in Abert's Squirrel (Sciurus aberti).

Melanism is widespread in different taxa and has been hypothesized to provide adaptive benefits in certain environments. Melanism is typically caused by mutations in one of two regulatory genes: the Melanocortin 1 Receptor (MC1R) or the Agouti Signaling Protein (ASIP). Melanism has repeatedly evolved among tree squirrels and their relatives (tribe Sciurini) in at least 12 different species based on our review of the literature. The causal mutations for melanism have been characterized in two species so far. This study examines Abert's Squirrel (Sciurus aberti), which has a melanistic morph whose genetic basis has not yet been established. We sequenced the MC1R and ASIP genes for five wild-type and seven melanistic S. aberti individuals to search for melanism-associated mutations. A novel single base pair mutation in the ASIP gene, unique to S. aberti, was found to be associated with melanism in the species, indicating that melanism in S. aberti evolved independently from other tree squirrels and thus represents an example of convergent evolution. The independent evolution of melanism in this species suggests that there is an adaptive advantage to the melanistic phenotype. The geographic range and habitat of S. aberti suggest possible benefits associated with thermoregulation, post-forest-fire camouflage, or other untested hypotheses.

Indigenous Genealogies of Relational Knowledge: Cedar Tree and Gray Squirrel as Important Relatives and Teachers

Indigenous peoples have education systems thousands of years old that have sustained our peoples in respectful relation with place. The backbone of our education systems is our stories and storytelling traditions. Beyond mere intellectual or analytical “texts” or “literature”, our stories place us in webs of relationships with sacred responsibilities. In this article, we discuss the importance of Indigenous genealogies of knowledge from both personal expertise and Indigenous Studies scholarship. We then describe a project on Yakama homelands in which Sahaptin storytelling is honored as a knowledge system that guides leaders and educators in their work. This project demonstrates the important role Indigenous stories can play in fostering more respectful and responsive systems. We argue that if educational programs or institutions wish to develop and remain in respectful relationships with Indigenous peoples and place, leaders and educators must learn to value, learn from, and lead with Indigenous knowledges.

Squirrels (Rodentia, Sciuridae) of the Early Miocene Tagay fauna in Eastern Siberia

The Tagay vertebrate fauna (Olkhon Island, Lake Baikal, Russia) dated to the late Early Miocene yielded a diverse association of sciurine rodents, including flying squirrel Hylopetes sp., tree squirrels Sciurus cf. lii, Sciurus sp., and Blackia cf. miocaenica, and a numerically dominant small marmotine Miospermophilus debruijni. The presence of flying and tree squirrels indicates the presence of wooded biotopes. The record of Blackia is remarkably distant (more than 4000 km) from the nearest synchronous records in western Asia (Anatolia) and Eastern Europe thus implying a continuous distribution range of this genus stretching through the middle latitudes of the Holarctic and likely marking the continental belt of temperate forests in late Early Miocene. Marmotines of North American origin document direct faunal communication between temperate faunas of the Old and New Worlds at that time.

A comprehensive database of squirrel distribution and occurrence in South Asia.

The Squirrels of South Asia (SOSA) database compiles comprehensive distribution and occurrence information on all squirrel species that occur in this region (34 species). These 34 squirrel species, including tree, flying and ground squirrels, represent 14% of global sciurid diversity. The database collates curated data from various sources such as museums, literature, primary fieldwork, citizen science and social media platforms and covers the entire distributional ranges of the target species, including countries in Central Asia and Southeast Asia when required. The SOSA database enhances our understanding of squirrel distribution, population dynamics and their conservation needs in South Asia by consolidating information. It aims to be a valuable resource for researchers, conservationists and wildlife enthusiasts. As of March 2023, the database comprises over 40,000 records of 34 species in over 30 countries globally. Spending an average of 334 hours on each species, more than 20 data collectors put in over 10,000 hours to gather, curate and build this database. The database has resulted in novel records of species occurrence in regions and countries that are poorly represented in currently available global data repositories. The current version which has been made public via GBIF comprises of 1187 records of all 34 species across multiple sources. This is a subset of the SOSA database.

Foraging Behavior Response of Small Mammals to Different Burn Severities

Wildfires cause profound challenges for animals to overcome due to their reliance on vegetation. This study addresses the impact of three levels of forest burn severity (unburned, low, and high burn severity) on the foraging behavior of small mammals in the Pinaleño Mountains (AZ, USA) using the giving up density (GUD) experiment approach. Overall, burn severity affected the foraging behavior of small mammals that spent less time foraging in high burn severity patches. Vegetation characteristics influenced GUD differently based on the level of burn severity. Higher canopy cover was perceived as areas with a higher predation risk (higher GUD) in unburned and low burn severity patches, while cover provided by logs and shrubs decreased the GUD (increased foraging). This suggests a complicated interaction between horizontal (logs, grass, shrub cover) and vertical vegetation cover in relation to burn severity. Fires affected the foraging behavior of the small mammals but did not impact all species in the same way. Generalists, such as Peromyscus sp. and Tamias dorsalis, seemed to forage across all burn severities, while specialist species, such as tree squirrels, tended to avoid the high burn severity patches. Clarifying the complex impacts of fires on small mammals’ foraging behaviors contributes to our understanding of the intricate interactions, at micro-habitat levels, between vegetation structure and the behavioral responses of animals and it can help managers to plan actions to reduce the negative impacts of wildfires.

The advantage of living in the city: effects of urbanization on body size and mass of native and alien squirrels

AbstractIn an ever more urbanized world, animals have to cope with different challenging conditions that may shape the individual’s phenotype in the urban environment. Since body mass and body size are found to be related to fitness in many species, investigating the variation in these two morphological traits along the rural-urban gradient, is a first step to understand how animals adapt to urbanization. Here we studied two tree squirrels, the native Eurasian red squirrel (Sciurus vulgaris) and the invasive Eastern grey squirrel (Sciurus carolinensis), using a pseudo-experimental design with replicated study sites (2 rural, 2 suburban and 2 urban sites for each species). We investigated whether squirrels differed in body size and body mass along the urbanization gradient and whether the invasive alien squirrels had more marked differences along the gradient, showing a higher adaptation capacity. We did not find variation in body size in red squirrels along the gradient, but invasive grey squirrels were slightly larger in urban than in other area-types. In both species, animals of either sex were heavier in the urban than in the rural sites, while the difference between urban and suburban areas depends on species and sex. Hence, morphologically both native and invasive species showed similar changes, with higher body mass in urban habitat, which could result in higher fitness, since body mass in squirrels species is positively related to reproductive success.

European ground squirrels Spermophilus citellus (Linnaeus) do not share identical Cryptosporidium spp. with North American ground squirrels.

Cryptosporidium Tyzzer, 1910 is one of the most common protistan parasites of vertebrates. The results of this study provide the first data on Cryptosporidium diversity in the European ground squirrel Spermophilus citellus (Linnaeus). A total of 128 faecal samples of European ground squirrels from 39 localities in the Czech Republic were analysed for the presence of Cryptosporidium spp. by microscopy and PCR/sequence analysis of small subunit ribosomal RNA (SSU) and the actin gene. While the microscopical examination did not reveal the presence of any Cryptosporidium oocysts, eight samples from six localities were PCR-positive. Phylogenetic analyses revealed the presence of five different Cryptosporidium spp. isolates. Four isolates, designated as Cryptosporidium sp. isolate Sc01-04, detected in wild populations and never recorded before, clustered closely to Cryptosporidium genotypes that have previously been found in North American ground squirrels' species. Cryptosporidium sciurinum Prediger, Ježková, Holubová, Sak, Konečný, Rost, McEvoy, Rajský et Kváč, 2021 was found in an animal sanctuary. Because C. sciurinum had previously been detected in Eurasian red squirrels Sciurus vulgaris Linnaeus at the same facility, it can be concluded that this Cryptosporidium was transmitted from tree squirrels to ground squirrels within the animal sanctuary. The results indicate that populations of European and North American ground squirrels are parasitised by different Cryptosporidium spp. At the same time, this is the first description of the occurrence of C. sciurinum in ground squirrels.

Cryptosporidium mortiferum n. sp. (Apicomplexa: Cryptosporidiidae), the species causing lethal cryptosporidiosis in Eurasian red squirrels (Sciurus vulgaris)

BackgroundCryptosporidium spp. are globally distributed parasites that infect epithelial cells in the microvillus border of the gastrointestinal tract of all classes of vertebrates. Cryptosporidium chipmunk genotype I is a common parasite in North American tree squirrels. It was introduced into Europe with eastern gray squirrels and poses an infection risk to native European squirrel species, for which infection is fatal. In this study, the biology and genetic variability of different isolates of chipmunk genotype I were investigated.MethodsThe genetic diversity of Cryptosporidium chipmunk genotype I was analyzed by PCR/sequencing of the SSU rRNA, actin, HSP70, COWP, TRAP-C1 and gp60 genes. The biology of chipmunk genotype I, including oocyst size, localization of the life cycle stages and pathology, was examined by light and electron microscopy and histology. Infectivity to Eurasian red squirrels and eastern gray squirrels was verified experimentally.ResultsPhylogenic analyses at studied genes revealed that chipmunk genotype I is genetically distinct from other Cryptosporidium spp. No detectable infection occurred in chickens and guinea pigs experimentally inoculated with chipmunk genotype I, while in laboratory mice, ferrets, gerbils, Eurasian red squirrels and eastern gray squirrels, oocyst shedding began between 4 and 11 days post infection. While infection in mice, gerbils, ferrets and eastern gray squirrels was asymptomatic or had mild clinical signs, Eurasian red squirrels developed severe cryptosporidiosis that resulted in host death. The rapid onset of clinical signs characterized by severe diarrhea, apathy, loss of appetite and subsequent death of the individual may explain the sporadic occurrence of this Cryptosporidium in field studies and its concurrent spread in the population of native European squirrels. Oocysts obtained from a naturally infected human, the original inoculum, were 5.64 × 5.37 μm and did not differ in size from oocysts obtained from experimentally infected hosts. Cryptosporidium chipmunk genotype I infection was localized exclusively in the cecum and anterior part of the colon.ConclusionsBased on these differences in genetics, host specificity and pathogenicity, we propose the name Cryptosporidium mortiferum n. sp. for this parasite previously known as Cryptosporidium chipmunk genotype I.Graphical

Jumping performance in tree squirrels: Insights into primate evolution

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

Shifts in fisher (Pekania pennanti) diet in response to climate-induced tree mortality in California assessed with DNA metabarcoding

A recent climate-induced tree mortality event in California, USA has led to dramatic landscape-level changes in the southern Sierra Nevada. Wide-spread conifer mortality was documented in habitat occupied by fisher (Pekania pennanti), a mature-forest associated species of conservation concern in this region. We analyzed fisher scats collected on the Sierra National Forest from the pre-tree-mortality period (PreTM, 2011 – 2013) and post-tree-mortality period (PostTM, 2017 – 2018). We used DNA metabarcoding to successfully identify taxa and summarized diet composition for 109 PreTM and 102 PostTM fisher scats. We observed 48 different diet items (33 assigned to species and 15 to genus). Mammals, birds, and plants of the Ribes genus (gooseberries and currents) comprised the highest proportions of diet items, although scats also contained DNA from reptiles, insects, arachnids, snails, and fungi. The frequency of occurrence of mammalian prey items was lower in PostTM (49.0%) versus PreTM scats (81.7%) with a reduction in the occurrence of two tree squirrels (Douglas squirrel and Humboldt’s flying squirrel). A higher proportion of scats collected PostTM (46.1%) contained DNA from Ribes spp. versus scats collected PreTM (19.3%). Our data reveal potential cascading effects of climate-induced tree mortality on fisher diet in the southern Sierra Nevada. Flexibility in fisher diet, however, may allow resilience to ecological change though future studies should consider the behavioral, energetic, demographic or fitness consequences from a shift away from medium-sized mammalian prey to plants.

Camera trapping efficiency in studying daily activity patterns of Turkestan lynx in the Northern Tien Shan

In order to determine the relationship between elusive carnivorans and other species, understand the mechanisms of their adaptation in the environment, as well as for regulation of strategies for rare carnivores’ conservation, it is relevant and necessary to study their daily activity rhythms. As a nocturnal species in the remote mountains of the Northern Tien Shan, the behavioral ecology and, in particular, the activity rhythms of the Turkestan lynx (Lynx lynx isabellina Blyth, 1847) are poorly studied. This article presents data on the daily activity of the lynx and an analysis of its correlation with the activity rhythms of its prey species in the Northern Tien Shan using camera traps. As a result of research conducted in Ile and Kungei Alatau from 2013 to 2022, we used 11,258 trap-days and obtained 59 frames with individual passages of Turkestan lynx and 528 frames with passages of its prey species – tolai hare (Lepus tolai), Siberian roe deer (Capreolus pygargus), Siberian ibex (Capra sibirica), wild boar (Sus scrofa), red tree squirrel (Sciurus vulgaris exalbidus) and red deer (Cervus elaphus). The rhythms of lynx’s daily activity coincided with the activity of its prey in three different time peaks: in the early morning, in the afternoon, and at night. Tolai hare in Kungei Alatau and Siberian roe deer in Ile Alatau play a significant role in the conservation of the lynx population. The results obtained prove the need to protect these six species to ensure the Turkestan lynx populations stability in the Northern Tien Shan. Keywords: Turkestan lynx, daily activity, specially protected natural areas, camera traps

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.