Winter habitats of bats in Texas

Abstract

Few studies have described winter microclimate selection by bats in the southern United States. This is of particular importance as the cold-adapted fungus, Pseudogymnoascus destructans , which causes the fatal bat disease white-nose syndrome (WNS), continues to spread into southern United States. To better understand the suitability of winter bat habitats for the growth of P . destructans in this region, we collected roost temperature and vapor pressure deficit from 97 hibernacula in six ecoregions in Texas during winter 2016–17 and 2017–18. We also measured skin temperature of Rafinesque’s big-eared bats ( Corynorhinus townsendii ), Townsend’s big-eared bats ( C . townsendii ), big-brown bats ( Eptesicus fuscus ), southeastern myotis ( Myotis austroriparius ), cave myotis ( M . velifer ), tri-colored bats ( Perimyotis subflavus ), and Mexican free-tailed bats ( Tadarida brasiliensis ) during hibernation to study their use of torpor in these habitats. We found that temperatures within hibernacula were strongly correlated with external air temperatures and were often within the optimal range of temperatures for P . destructans growth. Hibernacula and skin temperatures differed among species, with Rafinesque’s big-eared bats, southeastern myotis, and Mexican free-tailed bats occupying warmer microclimates and having higher torpid skin temperatures. For species that were broadly distributed throughout Texas, hibernacula and skin temperatures differed within species by ecoregion; Tri-colored bats and cave myotis in colder, northern regions occupied colder microclimates within hibernacula and exhibited colder skin temperatures, than individuals of the same species in warmer, southern regions. These data illustrate the variability in microclimates used as hibernacula by bats in Texas and suggest similar variation in susceptibility to WNS in the state. Thus, monitoring microclimates at winter roosts may help predict where WNS may develop, and where management efforts would be most effective.

External temperature and distance from nearest entrance influence microclimates of cave and culvert‐roosting tri‐colored bats (Perimyotis subflavus)

“…These results suggest that while microclimate temperatures are influenced by external temperatures in both caves and culverts, internal culvert temperatures are more strongly affected by external temperature. This supports datalogger data presented in Meierhofer et al () that indicates a correlation between external and internal temperatures in both caves and culverts, but with culverts having a stronger correlation with external temperature than caves. Thus, results presented in Meierhofer et al () suggest greater variability in culvert microclimates than in caves.…”

“…This supports datalogger data presented in Meierhofer et al () that indicates a correlation between external and internal temperatures in both caves and culverts, but with culverts having a stronger correlation with external temperature than caves. Thus, results presented in Meierhofer et al () suggest greater variability in culvert microclimates than in caves. Culverts may have greater variability in internal temperatures and be more greatly affected by external temperature as a result of their design (generally being straight, with two entrances to allow for air flow) and maintenance (clearing of brush around entrances), whereas not all caves have multiple entrances or may have additional barriers (vegetation) to reduce airflow.…”

“…Nevertheless, microclimate temperatures recorded by culvert‐roosting bats in this study fell within temperature ranges in which tri‐colored bats have previously been recorded (Webb, Speakman, & Racey, ). Tri‐colored bats are considered generalists in terms of their suitable range of temperatures for hibernation, potentially allowing them to utilize culverts as winter roosts where culverts are unsuitable for other species that have stricter temperature requirements (Meierhofer et al, ; Webb et al, ). Although air temperature may be more variable within culverts than caves, this variability does not preclude tri‐colored bats from using culverts as winter roosts.…”

“…Indeed, should climate change over time (Lindsey & Dalhman, ), tri‐colored bats may be in the position to compensate for rising temperatures by altering their location within a roost that remains within a suitable temperature profile. This may be of particular importance to culvert‐roosting tri‐colored bats, as external temperature appears to influence internal temperatures more so than in caves (Meierhofer et al, ). On a broader scale, our research speaks to the potential ways in which artificial roosts can replicate conditions of natural roosts and thus provide suitable habitats for hibernating bats.…”

“…The species is currently under review for listing under the Endangered Species Act by the United States Fish and Wildlife Service (USFWS, ). Tri‐colored bats are distributed throughout Texas and are unique in that they can be found roosting, not just in caves, but also in culverts (Demere et al, ; Meierhofer & Demere, ; Meierhofer et al, ; Sandel et al, ; Walker, Sandel, Honeycutt, & Adams, ). Culverts assist with drainage by allowing water to flow under roads.…”