A year in the thermal life of a free-ranging herd of springbokAntidorcas marsupialis

Abstract

We used miniature data loggers implanted in the abdominal cavity to measure core body temperatures at 30 min intervals in eight (three males, five females) adult free-ranging springbok Antidorcas marsupialis in their natural habitat, over a period of 11-13 months. The animals were subjected to a nychthemeral range of air temperature that often exceeded 20 degrees C, with an absolute minimum temperature of -6 degrees C and a maximum of 34 degrees C. Abdominal temperature exhibited a low amplitude (approximately 1.2 degrees C) nychthemeral rhythm, with a temperature peak near sunset and a trough shortly after sunrise. The amplitude of the nychthemeral rhythm of body temperature was not correlated with the 24 h range of air temperature. Although mean 24 h body temperatures were positively correlated with corresponding air temperatures, mean daily body temperature increased, on average, by only 0.02 degrees C per 1 degrees C increase in air temperature, so that it was only approximately 0.3 degrees C higher in summer than in winter. Mean monthly body temperatures were strongly positively correlated with photoperiod and, in parallel with changes in the time of sunrise, the times at which the minimum and maximum body temperatures occurred were shifted approximately 1.2 h earlier in summer than in winter. Annual and daily variations in body temperature of springbok, like those of other free-living African ungulates, therefore appear to reflect an endogenous rhythm, entrained by the light:dark cycle, but largely independent of fluctuations in the environmental thermal load. Springbok exhibit remarkable homeothermy and do not employ adaptive heterothermy to survive in their natural environment.