Thermoregulatory ecology of a solitary bat, Myotis evotis, roosting in rock crevices

1. Most studies of the thermoregulatory ecology of bats have been limited to laboratory experiments or studies of individuals roosting in artificial structures. 2. We investigated the interaction between thermoregulatory behaviour and roost choice in reproductive female Western Long-Eared Bats, Myotis evotis (H. Allen), roosting solitarily in natural rock crevices. The study was conducted in the badlands of the South Saskatchewan River Valley, Alberta, Canada, during 1997 and 1998. 3. Individuals used torpor every day and the amount of time spoilt in torpor was primarily influenced by the amount of time available to do so. Minimum body temperature was influenced by ambient temperature, although the form of this relationship differed between pregnant and lactating females. Pregnant females used deep torpor more frequently than lactating females. 4. All individuals roosted in rock crevices but pregnant and lactating females chose roosts that were different in structure and thermal characteristics. Pregnant females chose horizontal roosts that cooled at night but warmed quickly during the day, thus allowing passive rewarming from torpor. Lactating females chose vertical roosts that stayed warm at night when non-volant pups were present, thereby minimizing thermoregulatory costs to the young. 5. The behaviours observed are adaptive, but differ from those of other temperate-zone insectivorous bats that have been studied in the past. This highlights the importance of studying free-ranging animals living in natural habitat if we are to have an accurate view of thermoregulatory strategies and the importance of roost characteristics for roost-site selection.