WHY DO FEMALE BELDINGS GROUND-SQUIRRELS DISPERSE AWAY FROM FOOD RESOURCES

We examined the effects of food provisioning on the natal dispersal be havior of Belding's ground squirrels (Spermophilus beldingi). We provi ded extra food to adult and yearling females in their maternal territo ries during pregnancy and lactation, and to offspring of these females in their natal areas for 6 weeks after weaning. We used unprovisioned young of unprovisioned mothers as controls. Provisioning influenced t he probability of dispersal from the natal area by female but not male S. beldingi. All surviving male S. beldingi dispersed by 55 weeks of age, regardless of whether they and their mothers received extra food. By contrast, we observed a significant trend, beginning 3 weeks after weaning and continuing through the yearling year, for a greater propo rtion of provisioned than control female S. beldingi to emigrate from the natal area. Competition for food did not appear to influence natal dispersal of females. However, overall population density, density of females weaning litters, and rates of aggression and vigilance among these females, were higher in provisioned than control areas, suggesti ng that competition for non-food resources was unusually intense in pr ovisioned areas. We propose that juvenile female, but not juvenile mal e, S. beldingi may emigrate from the natal site to increase access to areas with low densities of conspecifics. Together with findings of ea rlier workers, our results suggest that spatial and temporal distribut ions of environmental resources are important influences on the disper sal behavior of female ground squirrels.