Survival tactics within thermally-challenging roosts: heat tolerance and cold sensitivity in the Angolan free-tailed bat, Mops condylurus

We studied roost microclimates, thermal preferences and temperature-related variation in body temperatures and flight abilities of M. condylurus from three roosts in man-made structures in South Africa. Roosts were characteri zed by marked spatio-temporal variability in ambient temperature and relati ve humidity on a daily and seasonal basis. Microclimates were thermally cha llenging, being very hot (>40 degrees C) for several hours daily in summer and autumn, and cold (<10 degrees C) for much of the night in winter. Therm al preference tests revealed that the bats actively selected temperature zo nes (35 degrees-42 degrees C) in which basal metabolic rate could be mainta ined, and above the minimum necessary for sustained flight. This presumably allowed them to minimize energy costs of thermoregulation without compromi sing reproductive activity or their ability to avoid predators. Bats displa yed pronounced heat tolerance and hyperthermia in response to prolonged exp erimental exposure to high temperatures (40 degrees C). They also exhibited cold-sensitivity, characterized by hypothermia and entry into torpor, when exposed to ambient temperatures below the thermal neutral zone. This respo nse to low ambient temperatures would conserve energy in cold periods when the high energetic costs of foraging may not be met owing to reduced insect availability. We hypothesize that this broad roosting tolerance has energe tic, ecological and evolutionary benefits that outweigh attendant disadvant ages, which are largely compensated for by an unusual physiology.