Effect of climatic conditions on the annual activity and hibernation cycle of Richardson's ground squirrels and Columbian ground squirrels

Abstract

In 1975 and 1976 the times of spring emergence, breeding, and entry into hibernation were compared for Spermophilus richardsonii and S. columbianus in an area of sympatry in the foothills of the southern Alberta Rocky Mountains. Both species emerged earlier in 1976, which had a warmer than normal spring, than in 1975, which had a cooler than normal spring. In both years S. richardsonii emerged earlier than S. columbianus and remained active longer. Juvenile S. richardsonii entered hibernation when 17–20 weeks old whereas juvenile S. columbianus were 10–11 weeks old. Yearling S. richardsonii bred, whereas yearling S. columbianus did not. Breeding success affected the time of entry into hibernation but not the time of emergence from hibernation in the next spring. A possible relationship between the periodic arousals during hibernation and the emergence pattern of squirrels in spring is discussed. The significance of flexibility of spring emergence, length of the active season, and age at breeding to survival and species ecology is considered.