Accordingly, mechanisms to encode the acoustic cues of individuality, range from amplitude 13, 14 and frequency modulations 15, 16 to the sequence of vocal units in songbirds 17, 18. In birds, evidence for individual acoustic variation in vocal signals exists in a wide range of species 11 and acoustic features of vocalisations are shaped by genetic, developmental and environmental factors 12. Accordingly, species living in larger groups have more signature information in their calls compared to species that live in smaller (even if more complex), social units 10. Discriminating among individuals is important for almost all social behaviours 9 and the evolution of vocal individuality has been shown to be related to the size of social groups 10. Vocalisations are also a prominent channel for signalling individual identity to conspecifics 3, 4, 5, 6, 7, 8. This approach could be further extended to study and understand vocal communication in other bird species.Īnimal vocalisations have the potential to provide a variety of information about age, body size, sex, social status and behavioural state of the emitter 1, 2. Our results suggest that studying the anatomical constraints that influence nesting penguin vocalisations from a source-filter perspective, can lead to a much better understanding of the acoustic cues of individuality contained in their calls.
The DFA also resulted in the further selection of 10 acoustic features for contact calls and 9 for display songs that were important for vocal individuality. The DFA correctly classified 66.1% of the contact calls and 62.5% of display songs to the correct individual. The acoustic parameters showing PIC ≥ 1.1 were used to perform a stepwise cross-validated discriminant function analysis (DFA). For each parameter, we calculated the Potential of Individual Coding (PIC). For each vocalisation, we measured 31 spectral and temporal acoustic parameters related to both source and filter components of calls. We recorded contact calls and ecstatic display songs of 12 adult birds from a captive colony. However, it is not clear which acoustic features of calls can encode individual identity information. In penguins of the genus Spheniscus vocalisations are important for social recognition. The African penguin is a nesting seabird endemic to southern Africa.
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