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.