Brain, abdominal and arterial blood temperatures of free-ranging eland in their natural habitat

Using implanted miniature data loggers we measured brain, arterial blood an d abdominal temperatures at 5-min intervals in two free-ranging eland (Trag elaphus oryx) in their natural habitat. The animals were subjected to a nyc hthemeral range of globe temperature which exceeded 40 degrees C. Arterial blood exhibited a moderate amplitude (2.3 degrees C) nychthemeral rhythm, w ith a temperature peak at 1600-1800 hours, and a trough in the early mornin g at 0600-0800 hours. Mean abdominal temperature was 0.2-0.3 degrees C lowe r than the corresponding blood temperature, and had a peak-to-trough amplit ude of 2.6 degrees C. Brain temperature closely paralleled changes in blood temperature but usually exceeded blood temperature by about 0.5 degrees C. Sporadic episodes of selective brain cooling occurred in one animal, but t he duration and magnitude of such cooling was small (less than 0.4 degrees C), and took place only well above the mode of blood temperature. Our resul ts do not support the concept that eland routinely employ adaptive heteroth ermy and selective brain cooling to survive in their natural environment.