Efficient sampling of avian acoustic recordings: Intermittent subsamples improve estimates of single species prevalence and total species richness

Abstract

Automated sound recording devices have become an important monitoring tool used to estimate species richness and abundance of birds in a variety of ecological and conservation studies. The prevalence of calls detected in a specific time period can be used as an index of relative abundance, to compare between populations. However, the statistical power to infer true differences in abundance between populations is low when detections are highly aggregated in time leading to high variance between samples from the same population. Here, we used two different sampling methods, and used the data from each to calculate species richness and acoustic prevalence of nine bird taxa from a total of 50 sound recordings. The first method simulated typical monitoring techniques used by observers in the field by using a continuous five-minute section of the recording. The second method used the first 10 seconds of each minute to create a composite recording, also of five minutes total duration. There was no difference in the mean prevalence index between methods. The intermittent samples, however, produced prevalence indices with a lower standard deviation (mean difference = 19 %), detected 26% more species per five-minute sample and required 60% less total listening time to detect as many species as the continuous method. The only cost of subsampling from a long recording is the extra digital memory and battery life required to obtain the recordings in the first place. Given that these costs are minor, the intermittent method holds much promise because it detects species more efficiently and provides greater power to detect differences in a species’ relative abundance, which in turn should allow for better-informed management regarding population status and trends.