SOCIAL-ORGANIZATION AND SPACE USE IN CALIFORNIA VOLES - SEASONAL, SEXUAL, AND AGE-SPECIFIC STRATEGIES

We intensively monitored space use and movement in Microtus californic us over a 2-year period that included 1 year of high density (maximum 618/ha) and one of low (minimum 5/ha); historically this population ha s exhibited cycles of 2 or 4 years. Adults of both sexes dispersed at the start of the breeding season, culminating in the establishment of intrasexually exclusive territories. In females, these territories per sisted throughout life, except that many young females recruiting duri ng the breeding season established contiguous, overlapping, or adjacen t home ranges with their mothers. This female philopatry explains the conclusion of previous workers that females of this species are non-te rritorial. In the dry (non-breeding) season, females had smaller range s that often overlapped and were clustered. Adult males moved breeding territories at a modal interval of 6 weeks; this is consistent with t heir avoidance of inbreeding with philopatric daughters. Ranges overla pped 1-4 adult females at any one time, and a cohort of 7 long-lived m ales overlapped an average of 16.4 females during their tenure on the grid. The period of maximum overlap with adult females varied among in dividual males. and did not correlate with the time of maximum body we ight. Ranges of males in the dry season overlapped extensively, with p ersistent associations among some individuals. In the low-density year , ranges of some adults failed to overlap intersexually. Juvenile male s dispersed gradually between 3 and 13 weeks of age (half before 9 wee ks), with some leaving after reaching sexual maturity; a few remained philopatric. Of juvenile females, 47% remained philopatric with the re st disappearing before 9 weeks of age. New understanding of vole socia l behavior, dispersal, and space use is achieved by focusing on the se asonal dynamics of spatial relationships among individuals with respec t to age, sex, and relatedness.