| Description |
The autecology and behavior of the rock squirrel, Spermophilus variegatus (Erxleben), was studied in northern Utah. The species was ecologically unknow despite its commonness and wide distribution. Behavioral patterns brought out in this study appear to substantiate subgeneric divisions. Similar distributions of Gambel oak (Quercus gambelii) and rock squirrels indicate that their distributions are inter-related. Optimal habitat requirements in northern Utah are rocky, south-facing slopes with oak thickets. Cut banks along roads are heavily utilized, resulting in alinear distribution is many areas. Rock squirrels spend the majority of their lives underground. burrows are usually constructed under boulders, discouraging digging predators. Burrows protect squirrels from harsh environmental conditions as well as predator. Rock squirrels, or their ectoparasites, have been implicated in several diseases common to man. Because of their potential for disease dissemination near residential areas, they should not be neglected in the event of zoonoses. Various types of mortality factors include predation, diseases, adverse weather, death during hibernation, agonistic behavior, accidents, and poisoning. Length of hibernation varies from one to six months, depending upon elevation and accessibility to food. Minimal rectal temperature of squirrels hibernating in the laboratory registered 43 F. Torpidity was sporadic, averaging 6-7 days per "sleep" period. Rock squirrels are indiscriminate in food choices during early spring, and become more selective as the variety of plants increases in late spring. Foliage and flowers are preferred in spring and early summer; fruits and seeds are selected in late summer autumn. Food consists almost exclusively of acorns in autumn. Insects and carrion comprise a small part of the diet. Breeding seasons depend upon age and altitude; adults and squirrels at lower elevations breed earlier. Mating occurs from one week to a month after emergence from hibernation and may be correlated with new pl;ant growth. Numbers of embryos averaged 6.1. (range 3-9), but young surviving to appear above ground averaged 4-5. Young are approximately 56 days old when they appear above ground. Mean weight of adults in the spring is about 550 g ; autumnal weight of adults is about 750 g. The mean home range size of adults is 0.67 acre, with males having slightly larger home ranges than females. Most young squirrels, especially males, disperse from parental home ranges at puberty. Ecological density of rock squirrels is 2.3 per acre during spring and 6.1 per acre prior to dispersal of young. Daily activity patterns vary with the season and weather conditions. Hourly activity on hot summer days is bimodal, with peaks in morning and late afternoon. Wind and precipitation also affect activity. Maintenance behavior includes postures, locomotion, grooming, feeding, and reaction to traps. Agonistic and mating behavior are described. Specific territories around home burrows are not defended, instead, squirrels appear to be intolerant only of those conspecifices that violate a certain distance surrounding each individual. A straight-line dominance hierarchy does not exist in local demes of rock squirrels. Communication between rock squirrels is not well-developed. Rock squirrels cause damage to some fruits, particularly apricots, when the trees are cultivated adjacent to squirrel habitats. Because of several behavioral characteristics, it is postulated that the species evolved as a more-or-less solitary animal, rather than from colonial stock. Contemporary occurrences of rather high populations are the result of man's environmental manipulations, rather than natural phenomena. |
