Assessing Summer and Winter Trends in Occupancy, Detection, and Activity of Threatened and Endangered Bat Species Across the United States

Abstract

Cave-hibernating bat populations in the eastern United States have been devastated by the spread of White-Nose Syndrome since the disease was first recorded in the country in 2006. Among impacted species, northern long-eared bats (Myotis septentrionalis) and tricolored bats (Perimyotis subflavus) have experienced some of the most dramatic declines in occupancy and abundance. To inform the management of threatened and endangered bat species, the United States Fish and Wildlife Service (USFWS) sets acoustic monitoring guidelines for presence/probable absence (i.e. detection/non-detection) surveys. Yet, as population levels of bats affected by White-Nose Syndrome continue to change over time, federal guidelines designed to protect threatened and endangered species must be periodically re-evaluated, along with the methodological frameworks used to create said guidelines. The goal of this dissertation is to aid in the development of future federal monitoring protocols for northern long-eared bats, Indiana bats (M. sodalis), little brown bats (M. lucifugus), and tricolored bats. To accomplish this goal, my first chapter compared methods for minimizing false negative results in acoustic surveys using four bat species as a case study: the northern long-eared bat, Indiana bat, little brown bat, and tricolored bat. My second chapter provides insights for winter acoustic monitoring guidelines for northern long-eared bats and tricolored bats in the Southeastern Coastal Plain. In my third chapter, I identify differences in winter activity patterns across USFWS Zones 1 and 2, where northern long-eared bats and tricolored bats may undergo hibernation or remain active year-round, in comparison with two species known to remain active throughout the winter season in the Southeastern Coastal Plain: southeastern myotis (Myotis austroriparius) and eastern red bats (Lasiurus borealis). I also assess the influence of temperature and precipitation on hourly activity levels in an effort to identify fine-scale temperature and precipitation thresholds of activity. I found that the standard frequentist framework for estimating level of effort (LOE) outperformed Bayesian and latency to detection (LTD) based approaches. My findings suggest that reductions in LOE requirements for future USFWS acoustic monitoring guidelines may be warranted for Indiana and northern long-eared bat presence/probable absence surveys. Furthermore, I found that monitoring efforts that follow protocols for northern long-eared or Indiana bats would also satisfy minimum requirements for little brown and tricolored bats, in the event that either species becomes listed in the future. Additionally, I found that northern long-eared bats, tricolored bats, southeastern myotis, and eastern red bats remained active throughout the winter across USFWS Zones 1 and 2. All four species demonstrated similar temporal activity patterns, with activity peaking from February to early March, followed by a pronounced decline by mid-March. This increase in activity may be indicative of spring staging behavior, which may occur one to two weeks earlier in the Southeastern Coastal Plain than more temperate regions. I was unable to identify precise hourly temperature thresholds to differentiate torpor from active behavior; however, I did record activity at exceedingly low temperatures. Findings from this dissertation will aid in the development of future monitoring protocols, as well as inform the management and conservation of threatened and endangered bat species in the eastern United States.