Intra- and inter-cave temperatures and locations used by hibernating Indiana bats: contextualizing disturbance, white-nose syndrome, climate, and optimal temperatures

We completed winter intracave surveys of Indiana bats ( Myotis sodalis Miller and Allen, 1928) over 40 years at seven important hibernacula in Indiana, USA. We documented locations and temperatures used by bats and found no patterns in cave morphology, intracave roost location, or temperature used by bats before or after advent of white-nose syndrome (WNS). Bats hibernated across a continuum of mid-winter temperatures, ranging from 0 to 11 °C. The mean temperature shifted from 5.95 ± 2.35 °C before WNS to 6.72 ± 2.05 °C after. Historically important hibernacula went from heavily populated (e.g., n = 98 250) to zero bats while others went from small populations to large (e.g., n = 2152 to 86 991). There was no clear set of optimal conditions for hibernation, and our data indicate historical determination of microhabitat preference was based on data obtained from distressed populations, many in refugia. Instead, favorable hibernacula provide a continuum of microclimates that meet needs varying by individual and over the season of hibernation. Such hibernacula support healthy individuals and individuals stressed by WNS. Conservation must move beyond a simplified energetics model of hibernation and embrace variable needs of individuals throughout hibernation. This study helps define preferred outcomes when managing thermal regimes of hibernacula.