BODY TEMPERATURE AND ACTIVITY PATTERNS IN FREE-LIVING ARCTIC GROUND SQUIRRELS

Abstract

We investigated influences of the thermal environment on patterns of body temperature (T b ), activity, and use of burrows during the active season in a population of free-living arctic ground squirrels (Spermophilus parryii). Arctic ground squirrels normally exhibited a daily 58C range in T b , and had higher T b when above ground than when in burrows (P , 0.0001). This difference decreased as standard operative temperature (T es ; an index of environmental heat load) increased. Ground squirrels entered burrows more frequently on warmer compared to average or cooler days and when T b exceeded 398C. On cool days with heavy precipitation, ground squirrels remained almost exclusively below ground, and peaks in T b were associated with brief aboveground forays. Time on the surface was maximal (about 80% between 0500 and 2200 h) at T es 17-338C and decreased proportionately with decreasing T es from 178C to 28C. Forty-six percent of variation in timing of presence above ground could be explained by a series of thermal and nonthermal variables related to environmental heat transfer. This suggests that diurnal activity patterns in this arctic environment with 24-h daylight result from a strategy that minimizes thermoregulatory costs.