Roosting and thermoregulatory behaviour of male Gould's long-eared bats, Nyctophilus gouldi: Energetic benefits of thermally unstable tree roosts

Information about the thermal biology of bats in relation to their roosting behaviour is scant. I used temperature telemetry to locate roosts and record the thermoregulatory behaviour of male long-eared bats, Nyctophilus gouldi (9 g), during late spring in the Northern Tablelands of New South Wales. Bats roosted under bark and in tree cavities, where they typically experienced wide daily fluctuations in ambient temperature (T_a). On 13 out of 16 days, bats employed two torpor bouts per day, during the early morning and late afternoon, coinciding with times of low T_a. Heating of roosts during the day resulted in up to 20°C of passive re-warming before active arousal and provided high T_a around midday when bats were normothermic. By switching between torpor and normothermic thermoregulation according to the daily T_a cycle, male N. gouldi appear to gain an energetic advantage from choosing poorly insulated and often sun-exposed roosts.