Population size assessment of Adélie penguin (Pygoscelis adeliae) chicks based on vocal activity rate index

Passive acoustic monitoring (PAM) is an effective method for bioacoustic researches. With the emergence of autonomous recording units (ARUs) and development of acoustic signal recognizer, PAM has been widely used in researches on conservation and ecology. However, challenges (e.g. extreme weather conditions) still remain in estimating species or population abundance based on acoustic monitoring. Adélie penguin (Pygoscelis adeliae) has been regarded as an ecological indicator in the Southern Ocean, and its population dynamics has ecological significance. We assessed the ability of an acoustic index, vocal activity rate (VAR), to estimate population size of Adélie penguin chicks on Inexpressible Island, Ross Sea, using acoustic data collected via ARUs. Linear mixed model analysis showed that VAR had a significant correlation with the abundance of penguin chicks and wind speed (conditional R2 = 0.743). This demonstrated that VAR could be effectively applied in assessing the population size of Adélie penguin chicks with wind speed being considered, affirming the effectiveness of PAM in monitoring the population dynamics of vocal species in extreme-climate regions.