Listening and watching: Do camera traps or acoustic sensors more efficiently detect wild chimpanzees in an open habitat?

Abstract

With one million animal species at risk of extinction, there is an urgent need to regularly monitor threatened species. However, in practice this is challenging, especially with wide‐ranging, elusive and cryptic species or those that occur at low density. Here we compare two non‐invasive methods, passive acoustic monitoring (n = 12) and camera trapping (n = 53), to detect chimpanzees Pan troglodytes in a savanna‐woodland mosaic habitat at the Issa Valley, Tanzania. With occupancy modelling we evaluate the efficacy of each method, using the estimated number of sampling days needed to establish chimpanzee absence with 95% probability, as our measure of efficacy. Passive acoustic monitoring was more efficient than camera trapping in detecting wild chimpanzees. Detectability varied over seasons, likely due to social and ecological factors that influence party size and vocalization rate. The acoustic method can infer chimpanzee absence with less than 10 days of recordings in the field during the late dry season, the period of highest detectability, which was five times faster than the visual method. Synthesis and applications. Despite some technical limitations, we demonstrate that passive acoustic monitoring is a powerful tool for species monitoring. Its applicability in evaluating presence/absence, especially but not exclusively for loud call species, such as cetaceans, elephants, gibbons or chimpanzees provides a more efficient way of monitoring populations and inform conservation plans to mediate species‐loss.

Automated detection of Hainan gibbon calls for passive acoustic monitoring

“…We address issues that are important to the overall usefulness of a classifier, including deciding how much data to manually label, data augmentation, operationally meaningful definitions of classifier success and the development of user‐friendly software. Our study provides an effective new monitoring method for the world's rarest primate, and also has wider applicability for applying deep learning to develop passive acoustic monitoring frameworks for other conservation‐priority loud‐call species such as cetaceans, elephants or other primates (Crunchant et al., 2020).…”

Introduction to the Special Issue on Savanna Chimpanzees

“…Savanna chimpanzee research also pushes the frontiers in the development of new research methods to study these apes. Faced with the challenges of a slow habituation process, researchers from Issa have been at the forefront of exploring the advantages of indirect methodologies (e.g., Bonnin et al 2018;Crunchant et al 2020) for studying savanna chimpanzee behavior. Vink et al (2020) continue this effort by measuring party sizes using three different methods for unhabituated individuals, including counts from direct observations, nest sites, and camera trap videos.…”

Identifying unknown Indian wolves by their distinctive howls: its potential as a non-invasive survey method

“…Therefore, it is of the foremost importance to have a statistically robust population estimation technique. However, widely used population estimation methods such as camera trapping and sighting-based distance sampling fall short in analysing population trends of certain elusive species or species living in extensive home ranges 3 , 4 . Many of these species are vocally active, which inspired scientists to study the effectiveness of an acoustics-based population abundance model for these species 5 – 8 .…”