Measuring subcutaneous temperature and differential rates of rewarming from hibernation and daily torpor in two species of bats

Prolonged and remote measurement of body temperature (T-b) in undisturbed small hibernators was not possible in the past because of technological limitations. Although passive integrated transponders (PITs) have been used previously to measure subcutaneous temperature (T-sub) during daily torpor in a small marsupial, no study has attempted to use these devices at T-b(s) below 10 degrees C. Therefore, we investigated whether subcutaneous interscapular PITs can be used as a viable tool for measuring T-b in a small hibernating bat (Nyctophilus gouldi Ng) and compared it with measurements of T-b during daily torpor in a heterothermic bat (Syconycteris australis; Sa). The precision of transponders was investigated as a function of ambient temperature (T-a) and remote T-sub readings enabled us to quantify T-sub-T-b differentials during steady-state torpor and arousal. Transponders functioned well outside the manufacturer's recommended range, down to similar to 5 degrees C. At rest, T-sub and rectal T-b (T-rec) were strongly correlated for both bat species (Ng r(2) = 0.88; Sa r(2) = 0.95) and this was also true for N. gouldi in steady-state torpor (r(2) = 0.93). During induced rewarming T-sub increased faster than T-rec in both species. Our results demonstrate that transponders can be used to provide accurate remote measurement of T-b in two species of bats during different physiological states, both during steady-state conditions and throughout dynamic phases such as rewarming from torpor. We show that, at least during rewarming, regional heterothermy common to larger hibernators and other hibernating bats is also present in bats capable of daily torpor. (C) 2015 Elsevier Inc. All rights reserved.