Monitoring Trends in Bat Populations of the United States and Territories: Status of the Science and Recommendations for the Future

Populations of bats (Order Chiroptera) are difficult to monitor. However, current recognition of the importance of bats to biodiversity, their ecological and economic value as ecosystem components, and their vulnerability to declines makes monitoring trends in their populations a much-needed cornerstone for their future management. We report findings and recommendations of a recent expert workshop on monitoring trends in bat populations in the United States and territories. We summarize selected case reports presented by others at the workshop, including reviews of methods and ongoing efforts to monitor a wide range of species of bats in a diverse array of situations. Most efforts at monitoring bat populations involve use of indices that are uncalibrated in relation to population size, do not incorporate measures of variation or detectability, are discontinuous in time and space, and sometimes lack standard protocols. This is in part because the complex and variable natural history of bats poses many challenges to monitoring. We also review principal findings and recommendations made by workshop participants. Recommendations centered on improving methods for monitoring populations of bats, defining objectives and priorities for monitoring gaining mandates for monitoring, and enhancing information exchange.