Passive acoustic monitoring of the endangered African penguin (Spheniscus demersus) using autonomous recording units and ecoacoustic indices

African penguins (Spheniscus demersus) are endangered and declining seabirds which make extensive use of vocal signals for intraspecific vocal communication. Accordingly, passive acoustic monitoring tools could be developed as robust population monitoring methods that cause minimal disturbance to the birds. In this study, we collected soundscape recordings at the Stony Point penguin colony (Betty’s Bay, South Africa) during the breeding season in 2019 (i) to document the circadian rhythms of vocal activity of this species (ii) to investigate whether the magnitude of variation of three different ecoacoustic indices correlates with the number of ecstatic and mutual display songs counted in recordings, which might inform on the breeding activity of the colony. Indeed, while ecstatic display songs are produced by males during intersexual competition and territorial defence, mutual display songs are given by parents returning to the nest after foraging trips. We found that the vast majority of the display songs (>80%) occurred between 04:00-08:00 and 17:30-21:30. We also found that the Acoustic Entropy index was a good predictor of the number of penguins’ songs within a recording. Overall, our study shows that African penguins vocalisations have the potential to assist the monitoring of this species while minimising disturbance.