CALIFORNIA GROUND-SQUIRREL BODY-TEMPERATURE REGULATION PATTERNS MEASURED IN THE LABORATORY AND IN THE NATURAL-ENVIRONMENT

Body temperature (T-b) was measured by telemetry in both laboratory ma intained and natural environment California ground squirrels, Spermoph ilus beecheyi. Laboratory animals had a mean diurnal T-b of 37.5 degre es C under conditions of LD 14:10, 20 degrees C and 36.5 degrees C und er conditions of LD 10:14, 20 degrees C (P < 0.01). Nocturnal mean T(b )s were 37.1 and 35.2 degrees C, respectively (P < 0.05). Mean diurnal T(b)s 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 s eason months of December through February. Natural environment hot sea son mean T-b was not significantly different from cool season mean T-b but both mean T(b)s were significantly different from the diurnal mea n T(b)s measured in the laboratory (P < 0.05). California ground squir rels exhibit an open-field stress induced hyperthermia in the laborato ry which can be extended for periods up to 6 h. The hyperthermic respo nse is blocked by L-propranolol at a dosage of 15 mg kg(-1). Laborator y animals do not habituate to repeated open-field exposures over a fiv e consecutive day period. It is suggested that stress hyperthermia mig ht be a normal component of thermoregulation in some free-living groun d squirrels because of the openness of the habitat in which they exist . (C) 1998 Elsevier Science Inc. All rights reserved.