Extreme regional heterothermy during flight in diverse wild bats.

Endotherms actively regulate their body temperatures to maintain relatively constant internal temperatures in heterogeneous environments, but experience regional variation in body temperature (heterothermy). This is especially pronounced in bats, which face locomotor and energetic challenges as the only flying mammals: cooling of the wing and its constituent muscles during flight could substantially impact performance and energetics. Here, we characterize thermoregulatory patterns in locomoting bats from 27 tropical and temperate species over a range of air temperatures by measuring core body temperature and wing muscle temperatures along a proximodistal axis. We find that bat core and wing temperatures are highly labile and are impacted substantially by air temperature. Measured wing muscle temperatures demonstrate the largest temperature gradient from core to locomotor muscle for active endotherms reported to date. These results expand our understanding of locomotor performance in bats, and suggest that thermoregulation and environmental conditions together shape locomotor performance in endotherms.