Activity and Thermoregulation of the Antelope Ground Squirrel Ammospermophilus leucurus in Winter and Summer

Antelope ground squirrels rely on their extremely labile body temperatures (Tb) to help maintain activity and energy balance at all seasons of the year. In summer, antelope ground squirrels employ hyperthermia to lengthen the duration of periods of surface activity by increasing the capacity for heat storage. The extent of hyperthermia increases with increasing environmental temperature. Periodically, the animals dissipate the stored heat passively by conduction in an underground burrow. This cycling of Tb allows them to remain active in environmental conditions intolerable on a steady-state basis. The limits of Tb apparently are adjusted to allow adequate durations of surface activity as well as rapid heat loss when the animals enter burrows, thus maximizing the ratio between time spent active and time spent dissipating heat. In winter, ground squirrels realize energy savings by lowering Tb at night to 32–33 C.