Vocal repertoire and acoustic cues to individual identity in the Northern Rockhopper penguin (Eudyptes moseleyi)

Abstract

Northern Rockhopper penguins (Eudyptes moseleyi) are highly vocal seabirds. However, detailed descriptions of their vocal repertoire are currently unavailable. Here, we studied the vocal behaviour of this species and assessed the presence of acoustic cues of individuality across different vocal types. We collected audio and video recordings from an ex-situ colony at the Two Oceans Aquarium (Cape Town, South Africa) consisting of wild rescued individuals and their offspring. We combined the visual inspection of spectrograms with spectro-temporal acoustic analyses based on a source-filter theory approach. Our results showed that the vocal repertoire of the Northern Rockhopper penguin is made of three discrete vocal types: agonistic calls, uttered during agonistic interactions, contact calls, produced to maintain acoustic contact among group members when visually isolated, and ecstatic display songs, mediating territorial defence and mate attraction. Moreover, we demonstrated that all vocal types encode acoustic cues to the individual identity of the emitter. Studying the vocal repertoire of penguins is crucial for a deeper understanding of their social behaviour and may ultimately contribute to the conservation of this endangered seabird.