Factors Influencing the Relative Abundance, Migration Phenology, and Roosting Ecology of Bats in the Midwest, with a Focus on the Indiana Bat

Pettit, Joseph

Some influences of bat presence in a particular area include the geographic range of the species, competition, life history, time of year, suitability of habitat, and disturbance. These influences are not mutually exclusive and many can be acting on assemblages of bats at once. In this study, our goal was to describe a number of these influences and their impact on Midwestern bats, focusing specifically on the Indiana bat (Myotis sodalis). First, we examined the impact of white-nose syndrome, an emerging fungal disease, on the capture rates of common bat species in central Indiana. We use capture data from eight years prior to white-nose syndrome arrival and four years of white-nose syndrome presence to compare the relative abundance change among species. We also examined the change in relative captures of each reproductive class within each species to assess the impacts of white-nose on reproduction. We found significant decreases in the relative captures of Indiana bats and little brown bats (Myotis lucifugus) and a significant increase in the relative capture rate of the Eastern red bat (Lasiurus borealis) during the white-nose period which gives an indication of their relative susceptibility to the disease. We also observed significant increases in the number of non-reproductive female little brown bats, northern long-eared bats (Myotis septentrionalis), Eastern red bats, and big brown bats (Eptesicus fuscus) indicating that white-nose syndrome may be causing pregnant females to lose pups during pregnancy. Second, we examined the influence of weather and time of year on the arrival and departure of Indiana bats at a summer maternity colony site in central Indiana. We used emergence count data to track the timing of bat presence and colony presence during the spring and fall migration seasons. We used an information theoretic approach to compare 23 models of weather, climate, and illumination predicting bat presence on the summer landscape. This study provides evidence that bats are embarking on spring and fall migrations to the maternity colony area at approximately the same time each year, and variation can be accounted for by changes in temperature, wind speed, and precipitation. Finally, we use dendrochronology to describe roosts of the Indiana bat at three sites across the range. We sample 33 roosts in central Indiana, 34 roosts in the southern Appalachian Mountains, and 30 roosts at Great Swamp National Wildlife Refuge in New Jersey. Indiana bats used different species at each site but appear to be choosing roosts based on tree size rather than roost age. Indiana bats use both early and late successional species at each site and managers should take advantage of both successional types to quickly establish and maintain a steady supply of roosts.