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This is the most thorough treatment ever undertaken on the Sciuridae and promises to be the definitive book on squirrels for decades to come. Squirrels of the World, written by scientists with more than 100 years of collective experience studying these popular mammals, is the first comprehensive examination of all 285 species of squirrels worldwide. The authors reveal virtually every detail of the family Sciuridae, which includes ground squirrels, tree squirrels, flying squirrels, prairie dogs, and chipmunks. Each species—from the familiar gray squirrel of American backyards to the exotic and endangered woolly flying squirrel of Pakistan—is described in a detailed account that includes distinguishing characteristics, ecology, natural history, conservation status, and current threats to its existence. Squirrels of the World includes • stunning color photographs that document rare and unusual squirrels as well as common varieties • evolution, morphology, ecology, and conservation status • colorful range maps marking species distribution • images of the skull of each genus of squirrel • extensive references

Otospermophilus douglasii (Richardson, 1829), the Douglas ground squirrel, was first described as a species and then relegated to a subspecies of the California ground squirrel, O. beecheyi (Richardson, 1829). However, genetic data recently were interpreted as indicative of returning O. douglasii back to valid species status. This semi-fossorial, social species is brown with small white spots, a dark dorsal patch, and silvery shoulders. Occupying diverse habitats and elevations, this native species is an important prey species and is most abundant in grasslands and open woodlands. It forages primarily on seeds and vegetation but is also in conflict with humans as a crop pest and disease vector that damages infrastructure through creating elaborate burrow systems. Currently, the International Union for Conservation of Nature has not provided a conservation assessment for O. douglasii.

We investigated age-specific variation in survival of dominant individuals in a long-lived and monogamous mammal, the alpine marmot (Marmota marmota), from a large dataset collected during a 24-year intensive monitoring of a free-ranging population. We found evidence of actuarial senescence in dominant individuals for both sexes. Survivorship was constant with age until dominant marmots were between 6 and 8 years of age and declined markedly thereafter. No between sex differences occurred in the intensity of actuarial senescence, which might be related to the weak intensity of sexual selection in this socially monogamous mammal. More investigations are needed to know whether cooperative breeding, hibernation, and monogamy, which are key features of the alpine marmot life history, could have shaped the patterns of actuarial senescence we report.

Over their lifetime, individuals may use different behavioural strategies to maximize their fitness. Some behavioural traits may be consistent among individuals over time (i.e., ‘personality’ traits) resulting in an individual behavioural phenotype with different associated costs and benefits. Understanding how behavioural traits are linked to lifetime fitness requires tracking individuals over their lifetime. Here, we leverage a long-term study on a multi-year living species (maximum lifespan ~ 10 years) to examine how docility (an individual’s reaction to trapping and handling) may contribute to how males are able to maximize their lifetime fitness. Cape ground squirrels are burrowing mammals that live in social groups, and although males lack physical aggression and territoriality, they vary in docility. Males face high predation risk and high reproductive competition and employ either of two reproductive tactics (‘natal’ or ‘band’) which are not associated with different docility personalities. We found that although more docile individuals sired more offspring on an annual basis, docility did not affect an individual’s long-term (lifetime) reproductive output. Survival was not associated with docility or body condition, but annual survival was influenced by rainfall. Our findings suggest that although docility may represent a behavioural strategy to maximize fitness by possibly playing a role in female-male associations or female mate-choice, variations in docility within our study population is likely maintained by other environmental drivers. However, individual variations in behaviours may still contribute as part of the ‘tool kit’ individuals use to maximize their lifetime fitness.SignificanceMale grouping is rare in animal societies, and represents a form of cooperation and social tolerance among males who are typically intolerant of one another and compete aggressively for reproductive access to females. However, Cape ground squirrel males lack physical aggression and live all year-round in either mixed-sex or all-male groups. We examined the association between docility and reproductive success and survival to investigate whether docility is beneficial to males. We found that more docile males sired more offspring on an annual basis, but docility was unrelated to lifetime reproductive success and survival. These findings indicate that docility may represent a behavioural strategy used to maximize reproductive success in a group-living ground squirrel. However, the benefit of docility variation is nuanced in this species.

Animals living in harsh or unpredictable environments adopt adaptive strategies to improve their fitness, with behavioral variation playing a key role in shaping individual outcomes. We examined whether between-individual variation in behavioral traits (personality) was associated with reproductive success and survival in female Cape ground squirrels (Xerus inauris). Using a 10-year dataset (2011–2021), we quantified behavioral expressions of the animal's response to trapping and handling (trap response, as a proxy for docility), trapping rate (trappability, for boldness) and the number of different trapping locations an animal was trapped at (trap diversity, for exploration) and examined their associations with (1) annual reproductive success, (2) lifetime reproductive success, (3) annual survival, and (4) on-site persistence (a proxy for lifespan). Response measures taken during transfer from the cage, handling by a human observer, and whether individuals ran or walked after release were moderately repeatable. Trappability was also repeatable, while trap diversity was not. Trap response and trappability were positively correlated with survival, but not reproductive success. Females that easily transferred from the trap to the handling bag (more docile) had higher annual survival, while those that ran after release had longer lifespans. Individuals trapped at a higher rate (bolder) had higher annual survival. The absence of a relationship between behavioral traits and reproductive success in females suggests that other factors, such as group dynamics, social interactions, and maternal effects, may be more influential in explaining the high reproductive skew in female reproductive success. Overall, our findings highlight the role of individual behavioral variation in shaping survival outcomes while emphasizing the need for further research into the mechanisms driving reproductive success in this species.

Seasonally breeding mammals must make constant adjustments in behavior and physiology to manage energetic trade-offs between survival and reproduction. Despite encountering high levels of climate and resource variability across the year, specialist Abert’s squirrels (Sciurus aberti), lack the capacity to express hibernation or pronounced morphological adaptations to seasonality. Using accelerometer and GPS devices, we assessed how abiotic environmental factors, reproduction, and resource abundance influenced levels of activity and daily range size in a rural and food-supplemented suburban population of squirrels. We also quantified fecal cortisol metabolites (FCM) in squirrels to assess patterns of glucocorticoid secretion. While changes in weather predicted activity levels in both populations, seasonal variation in activity levels were reduced in food-supplemented compared to rural squirrels. In contrast to activity, daily range size was not affected by weather but was a better predictor of sex-specific reproductive investment. Comparisons between populations suggest that food-supplemented squirrels forage more efficiently within smaller areas. Across both sexes and populations, squirrels showed no sexual dimorphism in body size, no major patterns of seasonal weight change, and no associations between body mass and FCM concentrations; however, FCMs were lower in the food-supplemented compared to rural population during late-spring. Taken together, activity levels and FCM concentrations appear primarily influenced by weather and seasonal fluctuations in food availability, whereas daily range size reflects sexual asymmetries in seasonal reproductive investment. Overall, squirrels appear to rely largely on behavioral adjustments to cope with novel environmental heterogeneity, rather than changes in morphology or GC secretion.

As the dominant predator on North America's grasslands, coyotes Canis latrans have a large influence on biodiversity, both on working ranches and in protected parks. Ground squirrel (sciurid) species and livestock carrion are often abundant on grasslands worldwide and have the potential to influence a predator's consumption of alternative prey. We collected 1321 scats in four seasons over two years in and adjacent to Grasslands National Park, Saskatchewan, to test the hypothesis that seasonal and spatial variation in consumption of sciurid prey and cattle Bos taurus carrion influenced coyote consumption of alternative prey. Sciurid (black‐tailed prairie dog Cynomys ludovicianus and Richardson's ground squirrel Urocitellus richardsonii) remains were common from spring to fall and had a strong inverse relationship with deer (mule deer Odocoileus hemionus and white‐tailed deer O. virginianus), which were most common in winter scats. Cattle remains were most common during spring, fall and winter, and occurred in 10.6% of scats annually. Biomass estimates suggest that cattle was the highest ranked food on cattle grazing land year‐round, and the 2nd ranked food, after deer, during winter on the portion of the park from which cattle were excluded. Closer proximity of scats to a prairie dog colony increased the likelihood of prairie dog remains throughout the year and reduced the likelihood of cattle remains in scats from spring to fall, but not during winter. Individual differences in foraging and ranging behavior may explain the spatial distribution of prairie dog versus cattle in scats. Further work is needed to determine whether sciurid prey, deer, or livestock carrion support large predator populations on grassland habitats to a level that may negatively affect coexisting prey species, including species at risk.

Lifetime reproductive success (LRS) in the form of number of descendants is a commonly used measure of individual fitness, but the life stage at which descendants are counted varies among studies. Conceptual and logistical trade-offs exist along the gradient of proximal-to-distal LRS metrics. Although proximal metrics, such as number of offspring weaned, are logistically easier to collect than distal metrics, such as number of reproductively mature offspring or grandoffspring, they may be of little evolutionary significance if stochastic events heavily influence the realized number of descendants. We use a 25-year demographic data set based on 954 adult female Richardson’s ground squirrels (Urocitellus richardsonii) from 22 annual cohorts to characterize and compare 6 metrics for LRS: lifetime production of litters, numbers of weanlings, weanling daughters, adult daughters, weanling matrilineal granddaughters, and adult matrilineal granddaughters. Most adult females weaned only 0 (21%), 1 (47%), or 2 (22%) lifetime litters. All LRS distributions were right skewed, with 53% and 77% of adult female Richardson’s ground squirrels having no adult female matrilineal descendants after 1 and 2 generations, respectively. Survival of daughters and mothers covaried with calendar year, and LRS was strongly influenced by the calendar year in which females recruited into the breeding population as yearlings. Catastrophic flooding in 2005 killed nearly all descendants from the 2004 and 2005 cohorts. Daughter survival to adulthood explained more variance in lifetime production of adult daughters and granddaughters than number, size, or sex ratio of litters. Overall, to have a ≥ 50% chance of 1 adult granddaughter, a female needed to produce 2 litters, 7 weanling daughters, or 2 adult daughters. All distal (response) versus proximal (predictor) LRS metrics had significantly positive relationships, but variability increased with each distal step in the response variable. Our long-term study highlights sampling issues with LRS studies, variability within and among cohorts, and the role of stochastic events in uncoupling a mammal’s reproductive effort from realized number of descendants.

Venous blood samples were collected from 64 apparently healthy juvenile Eastern gray squirrels (Sciurus carolinensis) after sedation with midazolam at the Wildlife Center of Texas located in Houston, Texas, during 2012. Blood gas (pH, PCO2, PO2, base excess, bicarbonate, oxygen saturation), electrolyte (sodium, potassium), biochemical (total CO2, ionized calcium, glucose), and hematologic parameters (hematocrit, hemoglobin, complete blood count) were determined using the i-STAT point-of-care analyzer. Sex did not affect any analyte. All squirrels recovered uneventfully and were successfully rehabilitated and released. Most values were as expected based on comparison to other young rodent species. These analyte data for healthy juvenile Eastern gray squirrels may be useful in assessment of Eastern gray squirrel population health and management and treatment of individual squirrels presented in need of medical care.

Abstract—Specific features of the sciurid auditory capsule have been analyzed based on 63 species from 20 genera. Its morphological specificity is characterized by a peculiar combination of primitive and advanced features stable within the group. They are (1) a rounded and inflated bulla with internal septa and a primitive attachment of the tympanic ring to the inner tympanic wall; (2) a transverse position of the bulla relative to the axis of the promontorium, resulting in the presence of deep petrosal fossae in front of and above the promontorium which are not covered by the tympanic bone; (3) a fully formed osseus facial canal and a developed bone tube of the stapedial artery; (4) the presence of a meato-cochlear bridge connecting the promontorium to the posterior wall of the acoustic duct which, in a fully developed form, does not occur in any other recent rodents; (5) pneumatization of the mastoid due to the expanding of the epitympanic chamber both anteriorly and posteriorly, with the formation of a premeatal pocket and a large epitympano-mastoid chamber divided into parts. The sciurid auditory capsule can generally be considered as morphologically advanced. Its diversity within the family concerns functionally significant features and is manifested in the structure of the external acoustic meatus, the size of the tympanic membrane, the length of the processes of auditory ossicles, and, most importantly, the degree of pneumatization of the auditory capsule. This is associated with quantitative variations of the characters and does not affect its structural plan, as a rule.