Identifying peaks in bat activity: a new application of SaTScan’s space–time scan statistic

Abstract

Context Identifying key spatio–temporal periods of an organism’s activity is an important focus of many ecological studies. Bat activity, as assessed by passive acoustic monitoring, can be extremely variable and currently there exists no agreed-upon method for identifying periods of high activity. Aims We proposed a new application for the space–time scan statistic (SaTScan) as an objective technique for identifying peak periods of bat activity. We aimed to test the validity of SaTScan as a method for identifying peaks in bat activity and demonstrate its use for assessing species-specific temporal patterns of activity. Methods To evaluate the effectiveness of SaTScan for detecting peaks in activity, we compared SaTScan to peaks identified with percentile thresholds. We evaluated peaks in activity across three scales: within nights; among nights at a site; and among sites. We applied SaTScan to demonstrate analysis of species-specific activity as further use of this technique. Key results SaTScan was effective at identifying peak time periods that included the majority of the high activity minutes. Timing of peaks of activity was most consistent for Myotis lucifugus during swarming and Lasiurus borealis during migration. All other activity for five species at three sites was indicative of foraging activity, with peaks in the first 5h after sunset. Conclusions SaTScan can be a valuable tool for quickly identifying peaks in acoustic activity of bats, with an objective, replicable and statistically sound method that can be applied at many temporal and spatial scales. Implications This tool has the potential for many more applications in ecology. Beyond acoustic analyses of bat activity, this technique could easily identify peaks in a research or management context, such as study activity among habitats, commercial developments or years at a single site.