How high is high? Using percentile thresholds to identify peak bat activity

Passive acoustic monitoring is a common tool used for monitoring bat activity levels. Identifying periods and locations of peak levels provides insight into bat ecology, and has important management implications. One limitation of passive acoustic monitoring is the relative nature of the data, often relying on subjective interpretation of descriptive terminology, such as “higher” or “lower.” We propose the use of percentile thresholds (PTs) for objectively identifying peak activity. By compiling a reference dataset, it is possible to define percentiles of the observed activity levels and these percentiles can provide objective thresholds for comparing activity levels. We used acoustic recordings from sites in Canada and calculated PTs based on the distribution of the number of calls per hour across all nights and sites for three species. Given species ecologies (e.g., hibernating, migrating) we were able to use PTs to objectively identify peak activity levels on a species-specific bas