Figure 1.

Annual patterns of core T_b of a representative male and female arctic ground squirrel together with double-plotted actograms of when T_b remained at euthermic levels (each row represents two consecutive days). For actograms, the x-axis is the time of day (hour) and black bars indicate intervals when T_b was above the mean. Blocks indicated by a and e during heterothermy of hibernation are torpor intervals that are expanded in the insert indicated by the arrow; b indicates the prolonged interval of euthermic T_b that occurs in males after heterothermy ends but before they emerge from their burrows; f indicates the post-emergence interval in females; g and c are mid active season intervals; d indicates when this male remained in the burrow prior to first torpor; h is the pre-immergence interval in this female. Box graphs b–d and f–h show the F—periodograms for rhythms of T_b that correspond to 10 day intervals indicated on the actograms and T_b traces. Black lines indicate the strength of rhythms (Q); curved grey lines indicate 95% confidence limit.