PARENT SESSION

Physiology 1 -- Session Chair: Thomas Tomasi-- University Center, Kate Buchanan Room

BEHAVIORAL THERMOREGULATION AND ACTIVITY PATTERNS IN FREE-LIVING ARCTIC GROUND SQUIRRELS. Ryan A. Long, Timothy J. Martin and Brian M. Barnes. Institute of Arctic Biology and Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, AK.

ABSTRACT- We investigated the hypothesis that arctic ground squirrels (Spermophilus parryii) strategically enter burrows to aid in thermoregulation during thermally stressful periods, both hot and cold, in the Arctic. From May-August of 2001 near the Toolik Field Station in northern Alaska, we continuously recorded activity and body temperature (T_b) patterns of 14 free-living arctic ground squirrels using light-sensitive radio collars and logging receivers (to indicate above vs. below ground position) and abdominally implanted temperature dataloggers. We simultaneously estimated operative environmental temperature (T_e) by recording temperatures of pelt-covered copper models of ground squirrels and collected climate variables with a weather station. Standard operative temperature (T_es), a more complete index of environmental heat load, was calculated from measured values of T_e and wind speed as well as previously published metabolic data. Arctic ground squirrels exhibited a labile T_b (range 5°C from daily minimum to maximum). During their active portion of the day, ground squirrels had higher T_b when they were above ground compared to when they were below ground (P < 0.0001); this difference decreased as T_es increased. Animals also entered burrows more frequently on hot days (T_es > 36°C) and when T_b exceeded 39°C. Body temperature decreased after entry into burrows. On cold days (T_es < 18°C) with heavy precipitation, animals remained almost exclusively below ground, and peaks in T_b were associated with brief above-ground forays. In addition, above-ground thermal conditions (T_es) strongly influenced percent of time animals spent in the burrow, with surface time becoming maximal between T_es 17 to 33°C and decreasing proportionately with decreasing T_es from 17 to -2°C. Use of a multiple regression model to control for the potentially confounding effects of other nonthermal variables did not qualitatively alter this pattern. These results support the hypothesis that arctic ground squirrels thermoregulate behaviorally, perhaps to minimize daily energy expenditure within the constraints imposed by their environment.

KEY WORDS: behavioral thermoregulation, arctic ground squirrel, Spermophilus parryii, standard operative temperature