Summer tree roost selection by Rafinesque's big‐eared bat

Abstract

Roost requirements of most North American forest bats are well-documented, but questions remain regarding the ultimate mechanisms underlying roost selection. Hypotheses regarding roost selection include provision of a stable microclimate, space for large colonies, protection from predators, and proximity to foraging habitat, among others. Although several hypotheses have been proposed, specific mechanisms likely vary by species and geographic region. Rafinesque's big-eared bat (Corynorhinus rafinesquii) commonly roosts in trees with large basal hollows in the Coastal Plain of the southeastern United States. Our objective was to weigh evidence for hypotheses regarding selection of diurnal summer roosts by Rafinesque's big-eared bat at 8 study sites across the Coastal Plain of Georgia, USA. We used transect searches and radiotelemetry to locate roosts and measured 22 characteristics of trees, tree cavities, and surrounding vegetation at all occupied roosts and for randomly selected unoccupied trees. We evaluated 10 hypotheses using single-season occupancy models and used Akaike's information criterion to select the most parsimonious models. We located 170 tree roosts containing approximately 870 bats for our analysis. The best supported model predicted bat presence from cavity size, interior wall texture, and number of entrances. Because large cavities allow bats to fly and smooth walls impede attacks by terrestrial predators, our results are consistent with the hypothesis that bats select roosts that allow them to evade predators. However, data on predation rates are needed for a conclusive determination. Because trees suitable as roosts for Rafinesque's big-eared bat are rare in the landscape, protection of suitable forested wetland habitat is essential to provide current and long-term roost tree availability. ß 2012 The Wildlife Society.

Adaptive response to land-use history and roost selection by Rafinesque’s big-eared bats

“…In most instances, 2 people inspected each cavity. Previous studies indicated that the probability of detecting Rafinesque's big-eared bats when they are present was 91-96% via inspection by 2 observers (Clement and Castleberry 2013;Fleming et al 2013b). The species, number, and position within the cavity (low, middle, or top) of all bats were recorded as were the species, DBH, tree height, decomposition state (live or dead), inside cavity dimensions (if possible), cavity texture, and cavity opening location (basal, basal and chimney, chimney only) of each potential roost tree.…”

“…Although we could not examine trees with chimney or upper bole cavities, these trees were included in the survey and in some of the analyses as they represent alternate roosts. All trees with basal cavity openings were inspected but only those with cavities > 2 m high and > 30 cm wide were included in the survey as smaller cavities are unlikely to be used (Clement and Castleberry 2013). Each tree with a sufficiently large cavity was marked with a numbered aluminum tag and its location was recorded with the Trimble GEO-XT GPS unit.…”

“…(Trousdale and Beckett 2005;Fleming et al 2013a). In general, Rafinesque's big-eared bats select roosts that are larger in diameter and have larger cavity volumes than randomly selected trees (Clement and Castleberry 2013;Fleming et al 2013a;Lucas et al 2015). However, there is considerable variation in sizes of trees used by Rafinesque's big-eared bats across study sites, with mean diameters ranging from 79 to 155 cm, almost a 100% difference (Trousdale 2011).…”

“…Developing effective plans that include these actions will rely on greater understanding of the factors that affect use and selection of roost sites and better models to predict presence of big-eared bats in an area. Recent studies suggest that landscape features such as distance to water, distance to roads, and distance to forest edge have little effect on roost selection by Rafinesque's big-eared bats (Clement and Castleberry 2013;Fleming et al 2013a;Lucas et al 2015). This suggests that concentrating on roost and habitat features (e.g., forest structure and composition, hydrological conditions) may be the best approach for developing conservation and restoration plans.…”

“…For example, in western Kentucky, bald cypress (Taxodium distichum) is the most commonly used tree (70.3%) for roosting (Johnson and Lacki 2013), whereas tupelo (Nyssa spp.) are the most commonly used roost trees in western Tennessee, Georgia, Louisiana, and South Carolina (> 86.5%- Gooding and Langford 2004;Carver and Ashley 2008;Clement and Castleberry 2013;Lucas et al 2015). In some sites, no particular species of tree is the dominant roost tree, and bats use a wide variety of tree species including oaks (Quercus), eastern cottonwood (Populus deltoides), American sycamore (Plantanus occidentalis), and Magnolia spp.…”