Structural and environmental predictors of presence and abundance of tri-colored bats in Texas culverts

Authors: Melissa B Meierhofer, Samantha J Leivers, Rachel R Fern, Lilianna K Wolf, John H Young, Jr., Brian L Pierce, Jonah W Evans, Michael L Morrison

The tri-colored bat (Perimyotis subflavus) is being reviewed for listing under the Endangered Species Act by the United States Fish and Wildlife Service. It is also listed as a species of greatest conservation need by the Texas Parks and Wildlife Department due to its susceptibility to white-nose syndrome (WNS) in other states. Several colonies of hibernating tri-colored bats have been documented roosting in culverts. Culverts are widespread in Texas as part of roadway infrastructure; thus, our objective was to understand and quantify which structural and environmental factors best explain culvert use and abundance of hibernating tri-colored bats in Texas. We selected and surveyed 207 culverts for presence of tri-colored bats using the Generalized Random Tessellation Stratified (GRTS) design and opportunistic sampling across 10 of 12 Texas level III ecoregions during the winters of 2016–2017 and 2017–2018. We recorded environmental and structural features of culverts at each site. We used a zero-inflated Poisson regression to identify which culvert features best explained presence and abundance of hibernating tri-colored bats. We found that number of culvert sections predicted presence of tri-colored bats. We also found that abundance of tri-colored bats was influenced by length of culvert, elevation, number of sections, portal height, portal obstruction, aspect, external VPD, external temperature, and NDVI. With the current threats to tri-colored bat populations, there is a need to consider management of culvert roosts. In addition, it is imperative to further investigate the potential susceptibility to WNS of culvert-roosting bats at more southern latitudes for local and regional planning efforts.