Preparing for hibernation: above ground activity and body temperature of free-living golden-mantled ground squirrels (Callospermophilus lateralis)

The annual cycle of obligate hibernators includes a prehibernation phase that remains poorly understood. To elucidate prehibernation behavior and physiology under natural conditions, we investigated patterns of above ground presence and body temperature (T_b) in free-living golden-mantled ground squirrels (Callospermophilus lateralis (Say, 1823)). We hypothesized that daily patterns of above ground presence and T_b, and transitions in these patterns as animals approach hibernation, reflect energy conservation strategies that are important to survival. We found that daily above ground presence and T_b were predicted by day length, ambient temperature (T_a), and soil temperature (T_soil), and that T_a and humidity explained variation in duration and timing of above ground presence. In the month prior to hibernation, animals reduced time spent above ground and time spent at high T_b, and progressively decreased T_b. Daily and transitional patterns differed between animals that survived until hibernation and those that died prior. Compared to animals that died, survivors spent less time above ground per day and exhibited faster and more pronounced decreases in T_b. Our results do not provide evidence for causes of mortality for those that died, but an extended active season and above ground presence may expose animals to predation risks.