The king penguin breeds without a nest in colonies of several thousand birds. To beg for food, the chick must recognise the parents in a noisy environment, without using visual and olfactory, only vocal, cues. The parental call has to be distinguished from among the calls of other parents and chicks and the display calls of mating pairs. This recognition process is made more difficult not only by these interfering noises but also by propagation problems due to the parent-chick distance and to the mass screen of birds which together impose a particularly difficult problem of acoustic communication. To study this recognition process, we have quantified some of the problems which the chick must solve. Firstly we described the main characteristics of parental calls. Secondly we measured the ambient noise of the colony in the feeding area. Thirdly, in this area, we studied the propagation of adult calls to analyse the degradation of the signal at different distances, quantifying the effect of the mass body screen by comparison with propagation in an open area. Then, we conducted experiments with chicks, establishing mean and maximum distances of detection of the parental call and testing their ability to detect parental calls in a "jamming'' situation, i.e. among extraneous adult calls. At last, we tested chicks to determine which are the main acoustic parameters involved in the recognition process of the parental call. Our results demonstrate that the noise in the colony is almost continuous, that it has a high sound pressure level and that the spectrum is occupied by numerous birds at a time. There is total masking effect in terms of frequency and amplitude, increasing the difficulty the chick has in detecting its parents. Nevertheless, the chick can compensate for this effect, since it is able to detect an information-carrying signal whose intensity is below that of a background noise with similar temporal and spectral characteristics. This process of perception against a background noise (i.e. the "cocktail-party'' effect) is linked to a coding-decoding of the parental call closely adapted to these particular environmental constraints.
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