Examining Bat Ecology in an Understudied Region: the Texas Gulf Coast
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I assessed activity and habitat associations of bats in and surrounding San Bernard National Wildlife Refuge on the Gulf Coast of Texas from May to August 2018 and 2019. My objective was to examine two major components of bat ecology in a region with no prior data: 1) nighttime activity and habitat use of all species and 2) day-roost use of evening bats (Nycticeius humeralis). I used autonomous acoustic detectors to assess nighttime activity of bats in various habitats across the refuge and recorded vegetation surrounding the deployment sites. I then conducted generalized linear mixed-effect models to assess drivers of bat activity. I also conducted Kruskal-Wallis non-parametric analysis of variance tests to determine differences in activity among habitats. For both analyses, I used the number of bat calls of each species in each year as response variables and habitat types and vegetation estimates as independent variables. Seven species of bats were detected and used all available habitats. Activity increased throughout the summer, likely because bat pups reached volancy. Alongside acoustics, I utilized radio telemetry to assess day-roost use of evening bats, an abundant species in the region. I radiotracked 11 evening bats to 9 unique roost locations. All bats roosted within a <1.0 km2 area of an urban neighborhood, 3–5 km from a protected area. No bats switched roosts, contrary to most literature, which documents regular roost switching in evening bats. Roost trees were over twice as tall and generally greater in DBH, with less surrounding canopy cover and nearly 20-fold less understory vegetation than trees in the protected area. This study has determined baseline ecological data surrounding bats in an area with no previous data. Acoustic detectors can continue to be deployed by biologists and allow long-term, year-round monitoring of bats. Repeated sampling of the refuge may allow researchers to examine changes in activity after the arrival of the disease white-nose syndrome. Preservation of large trees in the urban area has created bat roosts and allowed a population of tree-roosting bats to be present in a city. However, bats regularly use the protected tract of land potentially as foraging habitat. The combination of large trees with no understory clutter in the city and the preserved old-growth forest on the refuge may together provide the needed food and habitat resources for these bats. The telemetry study is the southernmost research on roosting ecology of evening bats, and as such, this population may be one of the first impacted by critical maximum temperatures.