Acoustic recording complements camera traps for monitoring sensitive penguin populations

Abstract

In the face of global biodiversity loss that threatens social–ecological sustainability, we must improve our knowledge of species’ behaviours, life histories and populations. Enhanced understanding is especially critical for taxa like seabirds that live in remote habitats where monitoring is logistically challenging, and technology-based approaches could lead to major advances. Considering conservation threats and breeding behaviours, penguins represent a promising taxon for further exploration of monitoring methods. Only five of 18 penguin species are currently considered species of Least Concern by the IUCN, and the sensitivity of penguins to ecological disturbances makes them important indicators of ecosystem dynamics. Penguins regularly congregate in dense breeding colonies and are visually and aurally conspicuous animals, making them relatively easy to monitor in some respects. In situ observations and visual remote sensing monitoring methods (i.e. camera traps, uncrewed aerial vehicles and satellite imagery) currently provide highly valuable information on penguin behaviour and population dynamics, but these methods have a number of shortcomings. Several rely on human presence in remote areas, some require clean lines of sight with no visual obstructions, and some offer limited spatial and temporal resolution. In this study we explore the use of passive acoustic monitoring (PAM) as a complementary remote sensing method to monitor penguin behaviour and populations at high spatial and temporal resolution without visual constraints or the need for continuous human presence. We conducted observations of vocalization rates and placed automated acoustic recorders in colonies of Magellanic Penguins Spheniscus magellanicus and Southern Rockhopper Penguins Eudyptes chrysocome in conjunction with camera traps. We found positive relationships between acoustic activity and counts of Magellanic Penguins in camera trap photos. We also identified clear diel patterns of acoustic activity that differed between breeding stages, and we found positive correlations between acoustic activity and estimates of colony density for various times of day and radii around recorders. While much work remains to improve this method and refine interpretation, PAM holds great promise as a complementary tool for monitoring the relative abundance and behavioural dynamics of penguins and other colonial animals, particularly those that burrow or nest in dense vegetation that impairs visual monitoring techniques.