California ground squirrel body temperature regulation patterns measured in the laboratory and in the natural environment.

Body temperature (Tb) was measured by telemetry in both laboratory maintained and natural environment California ground squirrels, Spermophilus beecheyi. Laboratory animals had a mean diurnal Tb of 37.5 degrees C under conditions of LD 14:10, 20 degrees C and 36.5 degrees C under conditions of LD 10:14, 20 degrees C (P < 0.01). Nocturnal mean Tbs were 37.1 and 35.2 degrees C, respectively (P < 0.05). Mean diurnal Tbs for each animal in the natural environment ranged from 39.3 to 40.1 degrees C (mean = 39.6 degrees C) during both study seasons which included the hot season months of March through August and the cool season months of December through February. Natural environment hot season mean Tb was not significantly different from cool season mean Tb but both mean Tbs were significantly different from the diurnal mean Tbs measured in the laboratory (P < 0.05). California ground squirrels exhibit an open-field stress induced hyperthermia in the laboratory which can be extended for periods up to 6 h. The hyperthermic response is blocked by L-propranolol at a dosage of 15 mg kg-1. Laboratory animals do not habituate to repeated open-field exposures over a five consecutive day period. It is suggested that stress hyperthermia might be a normal component of thermoregulation in some free-living ground squirrels because of the openness of the habitat in which they exist.