Differential selection of roosts by Eastern Small-footed Myotis relative to rock structure and microclimate

Roost selection by insectivorous bats in temperate regions is presumably influenced by roost microclimates in relation to thermoregulatory strategies, but few studies have included temperature measurements in habitat selection models. Rocky landscape features are an important source of roosts that provide both shelter from predators and beneficial microclimates for bats. Most information about rock-roosting bats is derived from western North America. We studied microhabitat selection by Eastern Small-footed Bats (Myotis leibii) on natural talus slopes and human-made stone structures in the Appalachian Mountains of Virginia and New Hampshire, relative to thermal and structural characteristics of rock crevices. Roosts were located with a combination of radio-telemetry and randomized visual surveys. Roost switching behavior and structural characteristics of roosts did not appear to be influenced by the methods we used to locate roosts. Compared to random crevices, both sexes selected crevices with narrow openings, likely to provide protection from predators. Reproductive females also selected larger rocks and more stable microclimates; whereas males selected crevices that were structurally similar to but warmed more during the day than random crevices. Rock size and other structural characteristics influenced temperatures of roosts and random crevices alike by inhibiting excessive daytime heating and nighttime cooling. Because large rocks were associated with roost selection by reproductive females, and talus slopes with large rocks could be limited, we recommend including rock size as a variable in landscape scale habitat assessments for Eastern Small-footed Bats. Protecting or managing for habitat features with large rocks that receive high solar exposure could benefit Eastern Small-footed Bats and perhaps other rock-roosting species.