Ecological Factors Affecting Annual Variation in Commencement of Hibernation in Wild Chipmunks (Tamias sibiricus)

Abstract

Annual variation in commencement of hibernation was observed for each sex-age class of the Siberian chipmunk ( Tamias sibiricus ) in an oak forest in northern Japan for 7 years (1973–1979). Neither air temperature, the duration of preparatory periods for hibernation, nor body mass were directly related to the annual variation. Hibernation began remarkably early in 1974 and 1975. These years were characterized by a population of chipmunks at high density and a failed crop of acorns. Competition for nest sites and low availability of food may be factors encouraging early hibernation. Adult females entered hibernation first, followed by adult males, juvenile females, then juvenile males. Adult males entered hibernation after 99.1% of females in their ranges had selected hibernation burrows. Males may need to confirm the location of the females’ burrows, and this could lead to greater mating success in spring, as chipmunks change hibernation sites yearly. Juveniles entered hibernation later than adults, perhaps because it was difficult for them to select burrows while adults were still active.