Spatial structuring and dispersal in a high density population of the California vole Microtus californicus

Abstract

Space use patterns of California voles are described from intensive live‐trapping data obtained during the late breeding season in a peak density year. Operational sex ratios were strongly female biased. Breeding males had mutually exclusive home ranges that overlapped the home ranges of one to several females. The average male home range was larger than the average female home range and tended to encompass female home ranges in their entirety. Breeding females had home ranges that often overlapped extensively with the home ranges of other breeding females. The degree of overlap, however, tended to be either very high or very low, indicating that groups of females may act territorially among themselves. Family groups that may include members of sequential litters formed at high density. Males on experimental removal grids had larger home ranges than males on the high density grids and some became wanderers while most females had home ranges comparable to those on the high density grids.Dispersers onto low density grids were not a random sample of the high density population; large breeding adults and small juveniles were under‐represented. No sex differences in dispersal were noted. Immigration into the high density populations was probably negligible.