Thermoregulation in free-ranging Nycteris thebaica (Nycteridae) during winter: No evidence of torpor

Abstract

Bats are among the most heterothermic mammals, with nearly all species investigated under free-ranging conditions to date exhibiting some degree of daily torpor and/or hibernation. We investigated thermoregulation during late winter by seven Nycteris thebaica in a warm, semi-arid habitat in northern South Africa, using temperature-sensitive transmitters to measure skin temperature (Tskin). Unexpectedly, we found no evidence for any expression of daily torpor or hibernation based on a total of 86 days of data from 7 bats (one male and six females), despite air temperatures as low as ∼10°C. Instead, daytime Tskin was distributed unimodally with most values in the 33–35°C range, and a minimum Tskin of 28.4°C at a roost temperature of 24.6°C. There are several possible reasons why N. thebaica may avoid torpor, including predation in roosts, and the long nightly foraging periods of this species compared to many others.