Gn. Bronner et al., Survival tactics within thermally-challenging roosts: heat tolerance and cold sensitivity in the Angolan free-tailed bat, Mops condylurus, S AFR J ZOO, 34(1), 1999, pp. 1-10
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.