A Comparison of the Efficiency of Mobile and Stationary Acoustic Bat Surveys

Abstract

Acoustic surveys with echolocation detectors have become a common method for monitoring bats worldwide. In the eastern United States, the spread of white-nose syndrome and the threat it poses for many bat species, particularly endangered species such as the Indiana bat (Myotis sodalis), has increased the need to monitor bat populations. Two popular methods, stationary and mobile surveys, are currently used by agencies in the United States to inform management and conservation efforts and by researchers to monitor and study bat populations. Despite the widespread use of these methods, no study has compared the efficiency in echolocation ‘capture’ success relative to human-hour of effort of these two methods. To compare these techniques we collected acoustic data with Anabat detectors in state forests of southern Indiana using stationary and mobile surveys in the way they are typically implemented. We compared the efficiency of each method at recording identifiable call files and Myotis bat call files per survey hour and hour of human effort, the proportion of call files recorded that were identified as Myotis bats, and the total number of bat species detected. Stationary surveys detected higher species richness, a higher proportion of Myotis bats, and were more efficient at recording Myotis bat call files per hour of effort than mobile surveys. Because of limitations in resources faced by many agencies, it is important to understand the efficiency of these methods relative to the effort expended implementing them. Whenever possible, we recommend the preferential use of stationary survey over mobile surveys.