ACTIVITY, BLOOD TEMPERATURE AND BRAIN TEMPERATURE OF FREE-RANGING SPRINGBOK

We used miniature data loggers to record temperature and activity in f ree-ranging springbok (Antidorcas marsupialis) naturally exposed to se vere nocturnal cold and moderate diurnal heat. The animals were active throughout the day and night, with short rests; the intensity of acti vity increased during daylight. Arterial blood temperature, averaged o ver many days, exhibited a circadian rhythm with amplitude <1 degrees C, but with a wide range which resulted from sporadic rapid deviations of body temperature. Peak blood temperature occurred after sunset. En vironmental thermal loads had no detectable effect on blood temperatur e, even though globe temperature varied by >10 degrees C from day to d ay and > 20 degrees C within a day. Brain temperature increased approx imately linearly with blood temperature but with a slope <1, so that s elective brain cooling tended to be activated at high body temperature , but without a precise threshold for the onset of brain cooling. Low activity attenuated selective brain cooling and high activity abolishe d it, even at high brain temperature. Our results support the concept that selective brain cooling serves to modulate thermoregulation rathe r than to protect the brain against heat injury.