Hormonal influences on natal dispersal in free-living Belding's ground squirrels (Spermophilus beldingi)

Preliminary identification of the physiological causes of natal dispersal in two populations of free-living Belding's ground squirrels (Spermophilus beldingi) was attempted in the Sierra Nevada of California. Two competing hypotheses, each suggesting a different endocrinological cause for natal dispersal in this species were tested. Data collected by observation, trapping, and telemetry during three field seasons (1979-1981) contradict predictions of the hypothesis that concurrent, high levels of circulating gonadal steroids cause natal dispersal. Rather the data suggest that perinatal exposure to androgen subsequently results in dispersal of treated individuals. The hormone may promote dispersal behavior through its mediating effects on juveniles' exploratory and social behaviors, and on their responsiveness to frightening stimuli. Possible interactions of endocrine mechanisms with other proximal and ultimate causes of dispersal are discussed.