Abstract:
Bats in hot roosts experience some of the most thermally challenging environments of
any endotherms, but little is known about how heat tolerance and evaporative cooling
capacity varies among species. We investigated thermoregulation in three sympatric
species (Nycteris thebaica, Taphozous mauritianus, and Sauromys petrophilus) in a
hot, semi-arid environment by measuring body temperature (Tb), metabolic rate and
evaporative water loss (EWL) at air temperatures (Ta) of 10 - 42 °C. S. petrophilus
was highly heterothermic with no clear thermoneutral zone, and exhibited rapid
increases in EWL at high Ta to a maximum of 23.7 ± 7.4 mg g-1 hr-1 at Ta ≈ 42 °C,
with a concomitant maximum Tb of 43.7±1.0 °C. T. mauritianus remained largely
normothermic at Tas below thermoneutrality, and increased EWL to 14.7 ± 1.3 mg g-1 hr-1 at Ta ≈ 42 °C, with a maximum Tb of 42.9 ± 1.6 °C. In N. thebaica, EWL began
increasing at lower Ta than in either of the other species, and reached a maximum of
18.6±2.1 mg g-1 hr-1 at Ta = 39.4 °C, with comparatively high maximum Tb values of
45.0±0.9°C. Under the conditions of our study, N. thebaica was considerably less heat
tolerant than the other two species. Among seven species of bats for which data on Tb
as well as roost temperatures in comparison to outside Ta are available, we found
limited evidence for a correlation between overall heat tolerance and the extent to
which roosts are buffered from high Ta.
