Figure 1.

Timing of hibernation seasons (mean dates ± s.e.) in AGSs at two nearby sites in Northern Alaska, approximately 68.5° N: Toolik Lake and Atigun River. Chronologies are shown separately for adult males and females and for young of the year (juveniles) of both sexes. (a) Autumnal entry into the hibernation burrow (hibernaculum), following cessation of above-ground activity, (b) initiation of heterothermy, (c) resumption of euthermy, following last torpor bout of spring, (d) emergence from the hibernaculum and resumption of surface activity, and (e) return to euthermy and emergence onto surface by non-reproductive juvenile females.