Acoustic recognition in macaroni penguins: an original signature system

Abstract

Penguins use vocal signatures as cues to identify their kin in dense colonies. Experimental studies of four species in two genera have pointed out that vocal signatures depend on the breeding ecology of the birds. Penguins that have a meeting site for pair members and chicks (genus Pygoscelis), as in many seabirds, have a less complex vocal signature than penguins that have no nests (genus Aptenodytes). To investigate whether this pattern would extend to other nest-building penguins, we studied the vocal signature in a species of the genus Eudyptes, the macaroni penguin, E. chrysolophus. Temporal and spectral features of signatures were analysed to determine which were likely to encode individual identity. Using a methodology derived from the theory of information, we measured and compared the amount of information given by each of these parameters by means of a stereotypy index. We then tested their effective efficiency in playback experiments of modified calls. Like Aptenodytes species, the macaroni penguins used a double coding system that integrated information in both the temporal and spectral domains. The encoding was made through the tempo given by the successive syllables of the call and the harmonic content of the call. However, information was not complementary but was mostly repeated in both domains, and variables were unidimensional as in Pygoscelis signatures. These results point out an original and simple signature system in macaroni penguins. Although they support the hypothesis of simpler systems in nest-building species they also reveal more subtle differences within this category.