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

Abstract

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.Échantillonnage efficace d'enregistrements d'oiseaux : le sous-échantillonnage intermittent améliore les estimations d'occurrence pour une espèce et de la richesse spécifique totale RÉSUMÉ. Les appareils d'enregistrement automatiques sont devenus des outils de suivi importants pour estimer la richessse spécifique et le nombre d'oiseaux dans le cadre de diverses recherches en écologie et conservation. La fréquence des chants détectés dans une période spécifique peut servir d'indice d'abondance relative, afin de comparer des populations. Toutefois, la puissance statistique à révéler les vraies différences d'abondance entre des populations est faible lorsque les détections sont très rapprochées dans le temps, ce qui engendre une grande variance entre les échantillons d'une même population. Dans la présente étude, nous avons utilisé deux méthodes différentes d'échantillonnage et les données provenant de celles-ci pour calculer la richesse spécifique et l'occurrence de neuf taxons d'oiseaux à partir de 50 enregistrements. La première méthode simulait la technique habituellement utilisée par les observateurs sur le terrain, soit l'écoute d'une section de 5 minutes continues de l'enregistrement. La seconde méthode reposait sur les 10 premières secondes de chaque mi...

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