Acoustic systems are adapted to breeding ecologies: individual recognition in nesting penguins

In all species of penguins studied to date, the display call, or parental call, has been demonstrated experimentally to facilitate identification between mates and between chicks and parents. We investigated parent-chick recognition in two nesting species, the Adelie penguin, Pygoscelis adeliae, and the gentoo penguin, P. papua. Through playback experiments, we tested the capacity of chicks to recognize the parental call at varying levels of background noise. By using modified calls, we found that chicks of neither species used temporal characteristics of the parental call (variations in frequency or amplitude with time) for individual recognition, but that both species used a simpler parameter, the pitch of the call. This finding contrasts with the more sophisticated use of acoustic cues by chicks of two non-nesting species, identified in earlier work. These differences in auditory processing of parental calls may have evolved because of different ecological constraints, particularly whether recognition of a nest site supports mutual identification of parent and offspring. (C) 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.