Natal dispersal in Columbian ground squirrels: is body mass the proximate stimulus?

Abstract

Data on body mass and dispersal history of Columbian ground squirrels (Spermophilus columbianus) were collected at five colonies in southwestern Alberta. Two colonies were studied from 1983 to 1990 and three from 1984 to 1986. Body mass of yearling male dispersers did not differ significantly from that of nondispersers. Among dispersers, heavier animals did not disperse before lighter ones. Extremely small animals, however, may delay dispersal until they are 2 years old. Timing of dispersal was not apparently related to body mass; dispersing squirrels showed a wide range in body mass, with dispersal occurring synchronously at all colonies in all years despite significant differences in body mass of yearlings between colonies. The apparent lack of evidence for a critical body mass threshold for dispersal led us to conclude that the timing of dispersal in yearling male Columbian ground squirrels is not controlled at the proximate level by achieving a set point in body mass.