Gray Bat (Myotis grisescens) Ecology and Movement in Southwest Virginia and Northeast Tennessee

Abstract

Gray bats (Myotis grisescens) are year-round cave-dwelling bats that were listed as federally Endangered in 1976 after massive population losses. The species greatly benefited from federal protection of caves and foraging habitat within its range following listing. Combined with an apparent resistance to White-nose Syndrome, a fungal disease that has decimated the populations of several other cave hibernating species, gray bat populations have been growing, and the species is now proposed for delisting. Nonetheless, gray bats also have been documented roosting in transportation structures which can complicate maintenance requirements. As gray bat populations grow, alongside a potential competition release as sympatric species dwindle, it is important to evaluate whether the species is expanding its expected regulatory range, what landscape variable combinations are preferred by them for foraging and for roosting, and whether they have seasonal patterns of landscape use. I explored these questions in Southwest Virginia and Northeast Tennessee, a region centered around a large maternity colony in Bristol, Virginia, through three main methods: acoustics, DNA barcoding, and radiotelemetry. Acoustic detectors were deployed across a large area over a longer period than the minimum United States Fish and Wildlife Service's recommended survey period, extending the survey season into November to capture patterns beyond the maternity season, and in a smaller area over three years to compare seasonal activity level patterns year-to-year. Acoustic surveys revealed recurring seasonal patterns each year with varying levels of activity and showed that gray bats foraged in areas outside their expected regulatory range, especially after pups became volant. I used DNA barcoding to determine bridge use by multiple bat species from guano deposited at the sites and explored which bridge features may be beneficial to bats. I determined structure use by three bat species and bridge width was the only structural feature that came up in a competing model, but it did not have a significant effect on bat use Finally, I used radiotelemetry to track whether gray bats were foraging near dammed impoundments as well as free-flowing riparian corridors by placing Motus radio towers at dams as well as rivers to passively detect whether tagged bats were present. I observed that gray bats did use impoundments as well as free-flowing rivers in the region for foraging. A network analysis revealed that gray bats across the season use the same foraging areas cohesively and some locations were corridors between areas of higher activity. These results indicate gray bats are expanding their range and highlight the importance of protecting connected riparian and reservoir habitats as the species continues to recover.