To study their thermal responses to climatic stress, we implanted seven greater kudu (Tragelaphus strepsiceros) with intra-abdominal, brain, carotid and subcutaneous temperature data loggers as well as an activity logger. Each animal also was equipped with a collar holding a miniature black globe thermometer, which we used to assess thermoregulatory behavior. The kudu ranged freely within succulent thicket vegetation of the Eastern Cape Province, South Africa. The kudu spontaneously developed a bacterial pneumonia, and consequent fever that lasted between six and ten days. The fever was characterized by a significant increase in mean 24-hour abdominal temperature from 38.9±0.2°C to 40.2±0.4°C (mean±SD, t₆=11.01, P<0.0001), although the amplitude of body temperature rhythm remained unchanged (t₆=1.18, P=0.28). Six of the kudu chose warmer microclimates during the fever than when afebrile (P<0.0001). Despite the selection of a warmer environment, on the first day of fever, the abdominal-subcutaneous temperature difference was significantly higher than on afebrile days (t₅=3.06, P=0.028), indicating vasoconstriction. Some kudu displayed increased frequency of selective brain cooling during the fever, which would have inhibited evaporative heat loss and increased febrile body temperatures, without increasing the metabolic maintenance costs of high body temperatures. Average daily activity during the fever decreased to 60% of afebrile activity (t₆=3.46, P=0.014). We therefore have recorded quantitative evidence for autonomic and behavioral fever, as well as sickness behavior, in the form of decreased activity, in a free-living ungulate species.