Cocktail–party effect in king penguin colonies

Abstract

The king penguin, Aptenodytes patagonicus, breeds without a nest in colonies of several thousands of birds. To be fed, the chick must recognize the parents in a particularly noisy environment using only vocal cues. The call an adult makes when seeking the chick is emitted at a high amplitude level. Nevertheless, it is transmitted in a colonial context involving the noise generated by the colony and the screening effect of the bodies, both factors reducing the signal–to–noise ratio. In addition, the adult call is masked by a background noise with similar amplitude and spectral and temporal characteristics, enhancing the difficulty for the chick in finding its parents. We calculate that the maximum distance from the caller at which its signal can be differentiated from the background noise (signal–to–noise ratio equal to 1) should not exceed 8–9 m in a feeding area. But our tests show that, in fact, chicks can discriminate between the parental call and calls from other adults at a greater distance, even when call intensity is well below that of the noise of simultaneous calls produced by other adults. This capacity to perceive and extract the call of the parent from the ambient noise and particularly from the calls of other adults, termed the ‘cocktail–party effect’ in speech intelligibility tests, enhances the chick's ability to find its parents.