Dispersal patterns of juvenile Townsend's ground squirrels in southwestern Idaho

Abstract

Understanding the effects of habitat reduction or fragmentation on animals requires some knowledge of their dispersal patterns. We used radiotelemetry to examine dispersal characteristics of 59 (37 male and 22 female) juvenile Townsend's ground squirrels (Spermophilus townsendii) on the Snake River Birds of Prey National Conservation Area in southwestern Idaho from April to June in 1993 and 1994. We tested for differences between years, sexes, and habitats in the rates and distances of dispersal. We compared the fates of dispersers and nondispersers and tested whether the direction of dispersal differed from random and whether the distribution of dispersal distances could be fitted to a two-parameter exponential function. Of the 38 animals for which dispersal status could be determined, 16 dispersed. The proportion of dispersers was greater for males than for females, but these rates did not differ by year or habitat type. We found no differences between habitats in dispersal distance. Survival rates through immergence into estivation did not differ between dispersers and nondispersers, suggesting that dispersal is not risky over the short term. Direction of dispersal did not differ from random, and the distribution of dispersal distances was adequately fitted to a truncated exponential distribution with a truncation distance of 118 m. Dispersers tended to end up in the habitat type that they started in, suggesting the possibility of habitat imprinting.