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4 Squirrel Behavior
- Johns Hopkins University Press
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Are squirrels social? Yes and no. The social systems of the 278 species of squirrels in the world range from completely asocial to highly social, with many permutations of sociality in between. Some live solitary lives except when mating; others live in complex social groups and have extensive social interactions with other members of the group. Ground squirrels. Among the most social of the squirrels are certain species of ground squirrels, marmots, and prairie dogs. Gail Michener, of the University of Lethbridge in Alberta, Canada, has been studying ground squirrels for 37 years, and has identified five grades of social organization among the ground squirrels: asocial, single-family kin clusters, female kin clusters with male territoriality, polygynous harems with male dominance, and egalitarian polygynous harems. Woodchucks and Franklin’s ground squirrels are classified as asocial, which means they are characterized by solitary living, no amicable interaction with other conspecifics (except mating ), and little amicable interaction with offspring. At the other end of the spectrum are the highly social black-tailed prairie dogs and the Olympic marmots. Yellow-bellied marmots, a frequently studied squirrel, are moderately social, living in polygynous harems with male dominance. These harems are composed of females, yearling young, babies, and a dominant male who defends his territory from potential usurpers. The females in a harem are most often related, and the social relationship among all members of the Chapter 4 Squirrel Behavior harem is almost always amicable. The older females in a harem tend to be the only breeding females, with the younger females being reproductively suppressed by the older females’ presence. The younger, nonbreeding females are important, though, in that they assist in the care of babies. The dominant male will act aggressively to yearling males, which encourages them to disperse. South African ground squirrels in southern Africa have been studied extensively by Jane Waterman, of the University of Central Florida, who has documented their social structure. Female South African ground squirrels live in all-female groups, similar to some other ground squirrels, which are made up of only related females and young. These females feed on communal ranges and live communally in several burrows, except during lactation when the female lives alone in a separate burrow. Females interact amicably and there is no identifiable hierarchy among them. The unique aspect of the South African ground squirrel social system are the males. Male South African ground squirrels do not live with females, but instead they live together in groups of up to 20 unrelated individuals of varying ages. Members of a male group share a common home range and forage together throughout this range. Although there is some hierarchy and dominance in these groups, interactions among males are largely amicable, with males grooming each other and sharing burrows. Among all ground squirrels, social behavior is similar. Some examples of social behavior among ground squirrels include play, grooming, vocalizations , and greeting (such as nose-to-nose or nose-to-mouth contact upon encountering another squirrel). Other social behavior involves group care of the young, such as communal nursing and communal hibernation. Because of the variation in the level of ground squirrel social systems, they are good research subjects for comparative studies. Daniel Blumstein, of the University of California, Los Angeles, and Kenneth Armitage, of the University of Kansas, did one such study in 1998, which compared life-history tactics across various species of social and nonsocial ground squirrels. In the study, they examined both the costs and benefits of living in a social group. One of the primary benefits of social living is increased survivorship . In fact, the authors state, “No matter how we examined the relationship , more socially complex species had a higher survival rate to age one.” Increased survivorship results from a decrease in predation due to a larger number of individuals to detect predators. It also results from an increase in cooperation, through allogrooming (which reduces ectoparasites) and cooperative care of young (to include communal nursing, young females as helpers, and communal hibernation). Social living comes with a cost. With many animals in a small area, the competition for resources, such as food, mates, and burrows, increases. This Squirrel Behavior 49 [44.222.149.13] Project MUSE (2024-03-19 14:10 GMT) 50 Squirrels: The Animal Answer Guide competition can lead to increased aggression, increased dominance, reproductive suppression of younger animals, and infanticide. John Hoogland, of the University of Maryland Appalachian Environmental Laboratory, reports that infanticide, mostly...