How to keep cool in a hot desert: Torpor in two species of free-ranging bats in summer

Small insectivorous tree-roosting bats are among the most taxonomically diverse group of mammals in Australia's desert, yet little is known about their thermal physiology, torpor patterns and roosting ecology, especially during summer. We used temperature-telemetry to quantify and compare thermal biology and roost selection by broad-nosed bats Scotorepens greyii (6.3 g; n = 11) and Scotorepens balstoni (9.9 g; n = 5) in Sturt National Park (NSW Australia) over 3 summers (2010–13). Both vespertilionids used torpor often and the total time bats spent torpid was ∼7 h per day. Bats rewarmed using entirely passive rewarming on 44.8% (S. greyii) and 29.4% (S. balstoni) of all torpor arousals. Both bat species roosted in hollow, cracked dead trees relatively close to the ground (∼3 m) in dense tree stands. Our study shows that torpor and passive rewarming are 2 common and likely crucial survival traits of S. greyii and S. balstoni.