Dena J. Clink

1 OVERVIEW Passive acoustic monitoring (PAM) has greatly advanced scientific research by allowing scientists to study sound-producing species over unprecedented spatial and temporal scales, even in remote and difficult-to-access ecosystems. PAM for biological purposes started in the 1960s, when marine researchers began using hydrophones to study cetaceans, especially large whales (Payne & McVay, 1971).

Apes on the Edge: Chimpanzee Life on the West African Savanna. Pruetz, J. 2025. University of Chicago Press, Chicago, IL. 160 pp. US$25.00 (paperback). ISBN 978-0-226-83751-2. State of the Apes: Disease, Health and Ape Conservation. White, A., S. Unwin, A. Lanjouw, K. Scholfield, and H. Rainer, editors. 2024. State of the apes. Volume 5. Cambridge University Press, Cambridge, UK. xxiv+429 pp. £29.99 (paperback). Free download from https://www.stateoftheapes.com/volume-5-disease-health-and-ape-conservation/.

1 Introduction Terrestrial applications of passive acoustic monitoring (PAM)—which utilize autonomous acoustic recording units (ARUs)—have increased dramatically in recent years (reviewed in Sugai et al. 2019). The use of ARUs allows for monitoring at spatial and temporal scales that are generally not achievable using human observers (Gibb et al. 2018). PAM has been used to investigate vocal behavior (Clink et al.