The Vocal Repertoire of the African Penguin (Spheniscus demersus): Structure and Function of Calls

Abstract

The African Penguin (Spheniscus demersus) is a highly social and vocal seabird. However, currently available descriptions of the vocal repertoire of African Penguin are mostly limited to basic descriptions of calls. Here we provide, for the first time, a detailed description of the vocal behaviour of this species by collecting audio and video recordings from a large captive colony. We combine visual examinations of spectrograms with spectral and temporal acoustic analyses to determine vocal categories. Moreover, we used a principal component analysis, followed by signal classification with a discriminant function analysis, for statistical validation of the vocalisation types. In addition, we identified the behavioural contexts in which calls were uttered. The results show that four basic vocalisations can be found in the vocal repertoire of adult African Penguin, namely a contact call emitted by isolated birds, an agonistic call used in aggressive interactions, an ecstatic display song uttered by single birds, and a mutual display song vocalised by pairs, at their nests. Moreover, we identified two distinct vocalisations interpreted as begging calls by nesting chicks (begging peep) and unweaned juveniles (begging moan). Finally, we discussed the importance of specific acoustic parameters in classifying calls and the possible use of the source-filter theory of vocal production to study penguin vocalisations.

Do penguins’ vocal sequences conform to linguistic laws?

“…Spectrograms of EDS were visually inspected in Praat v. 6.0.43 [27] by EF and EC. Using a one-layer TextGrid object, we assigned each vocal element to a syllable type based on its spectrotemporal features, as previously described in the literature [19,21]. Overall, we identified 7495 syllables (type-A = 4440; type-B = 1298; type-C = 1757).…”

“…The use of vocal sequences is also common in seabirds [18], despite the absence of evidence for vocal production learning. It is particularly prevalent in penguins [19], a family of non-flying seabirds that diverged from the main bird lineage approximately 71 Ma [20] and have evolved a complex vocal repertoire comprising both calls and display songs [19,[21][22][23]. Display songs are made of sequences of identical and redundant acoustic units, whose spectral envelope encode cues to the individual identity of the emitter [24].…”

The function of three main call types in common cuckoo

“…In non-Passeriformes, vocalizations are often simple and stereotyped, but messages can also be encoded in different call types. For examples, adult African penguin (Spheniscus demersus) employ four vocal categories for the use in different circumstances (Favaro, Ozella, & Pessani, 2014); male corncrakes (Crex crex) are known to express low or high levels of aggressive motivation in broadcast calls and soft calls, respectively (Rek & Osiejuk, 2011); and male ural owls (Strix uralensis) use different call types for territorial advertisement and for duetting with female (Lundberg, 1980). For cuckoos, a well-studied brood parasitic avian species, the temporal and frequency variables of male "cu-coo" calls ( Figure 1a) are well-known (Lei, Zhao, Wang, Yin, & Payne, 2005).…”

Vocal individuality and species divergence in the contact calls of banded penguins

“…Penguins use vocalisations for individual localisation, recognition, and to maintain social relationships and group cohesion (Jouventin, 1982;Favaro et al, 2014a). Based on the acoustic proprieties of their vocalisations and behavioural context of emission, four categories can be distinguished in the vocal repertoire of adult penguins (Jouventin, 1982): contact calls (uttered to maintain cohesion with the group or the partner), agonistic calls (made during fights and in territorial defence), as well as two types of display songs: complex vocalisations made of syllable sequences that can be uttered by single birds (ecstatic display songs), or by pairs (mutual display songs).…”