Roosting ecology of Rafinesque's big-eared bat and southeastern myotis in the Coastal Plain of Georgia
Clement, Matthew John
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Rafinesque’s big-eared bat (Corynorhinus rafinesquii) and southeastern myotis (Myotis austroriparius) roost in hollow trees in swamps in the southeastern United States, where they are designated species of concern by states throughout their range. I investigated the roosting ecology of these species, with an emphasis on structural and microclimate characteristics of roost trees and habitat characteristics affecting species abundance. I used transect searches and radio telemetry at 8 study sites across the Coastal Plain of Georgia during summer 2007 and 2008 to identify and characterize diurnal summer roost trees for both species. I found 170 Rafinesque’s big-eared bat tree roosts and 25 southeastern myotis tree roosts. I analyzed the relationship between structural characteristics of hollow trees and bat presence using a single season occupancy model. Rafinesque’s big-eared bats selected summer tree roosts with large cavity volumes and smooth interior walls, which is most consistent with the hypothesis that selection is related to predator evasion. Southeastern myotis tended to select water tupelo (Nyssa aquatica) trees with a large solid wood volume, which is most consistent with the favorable microclimate hypothesis. However, no tree structure variables were significant predictors of southeastern myotis presence, suggesting unidentified factors also affect roost selection. I placed temperature and humidity data loggers in 45 hollow trees during 2008. I used hierarchical linear and logistic models to model the relationship between tree structure and microclimate and between cavity microclimate and Rafinesque’s big-eared bat presence. Tree structure variables explained <25% of variation in microclimate. Microclimate varied among available trees, but played no identifiable role in Rafinesque’s big-eared bats roost selection. I modeled the relationship between number of bat colonies and landscape scale habitat variables using zero-inflated negative binomial regression. Colony density depended on duration of wetland flooding, wetland width, and study site. I generated predictive density maps to identify areas of high colony density and to estimate overall abundance. The 16,016 ha of forested wetland on the 8 study sites contained an estimated 2,190 colonies and 6,032 bats in trees with basal hollows, with density ranging from 0.04 colonies/ha in saturated wetlands to 0.27 colonies/ha in semi-permanently flooded wetlands.