DOI: 10.5061/dryad.37pvmcvpd
title: Differential selection of roosts by Eastern Small-footed Myotis relative to rock structure and microclimate

description: 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.
description: Free-ranging Eastern Small-footed Bats were located in their
 roost sites either using radio-telemetry or with visual searches. Roosts
 were categorized according to what could be inferred about the occupants
 when viewed from outside the crevice during visual searches, or based on
 physical examination in the case of captured individuals. For each roost,
 we measured the length, depth and height of the upper and lower rocks that
 formed the crevice, and the length, depth, width and orientation
 (categorized as horizontal, diagonal, or vertical) of the crevice. To
 reduce the number of variables we needed to model, we used a Principal
 Components Analysis to describe variation in the six rock variables, and
 we saved the resultant component scores as latent variables (PC 1 and
 PC2); these corresponded to overall size of the upper and lower rocks,
 respectively. Strong positive component scores indicate the largest rocks.
 We also recorded temperatures for a subset of crevices and for nearby
 ambient air on an hourly basis over 3 consecutive days to assess
 microclimates. Temperature variables in the dataset include 3-day averaged
 absolute measurements (average, maximum and minumum) and 3-day averaged
 relative measurements (calculated as temperature of the crevice minus
 ambient temperature) for overall, and at the hottest and coldest part of
 the day (relative average, relative minimum, and relative maximum).
 Temperature measurements were obtained after bats had vacated the roost
 and thus they portrayed the general thermal characteristics of the
 crevice, not the temperature when occupied. We collected the same
 structural and thermal measurements from a near equal number of randomly
 selected rock crevices within the same rock formations. 
description: The data files are .csv format, which are compatible with most
 spreadsheet software packages.