Counting the chorus: A bioacoustic indicator of population density

Passive acoustic monitoring has grown in utility for tracking wildlife populations, though challenges remain when using acoustic detections to monitor population size and density. Distance sampling is considered the 'gold standard' for estimating animal densities but has several important limitations. Here, we have compiled data and code from a case study that demonstrates a fast bioacoustic analysis method leveraging a simple metric call density. Using three years of synchronously collected bioacoustic and point-transect distance sampling data for eight forest bird species native to Hawai‘i, including four endangered species, we found strong correlations between call density and distance sampling-based animal density estimates. These findings indicate that call density is a reliable indicator of animal density that can be used independently or combined with traditional monitoring methods. This approach could enhance passive acoustic monitoring by providing more sensitive population health indicators than commonly used detection/nondetection methods, facilitating prompt conservation and management decisions.