Finding a parent in a king penguin colony: the acoustic system of individual recognition

To be fed, a king penguin, Aptenodytes patagonicus, chick must identify the call of its parents, in the continuous background noise of the colony. To study this recognition process, we played back to the chicks parental calls with acoustic parameters modified in the temporal and frequency domains. T he parental call is composed of syllables (complex sounds with harmonic ser ies) separated by pronounced amplitude declines. Our experiments with modif ied signals indicate that the chick's;frequency analysis of the call is not tuned towards precise peak energy values, the signal being recognized even when the carrier frequency was shifted 100 Hz down or 75 Hz up. To recogni ze the adult, chicks used frequency rather than amplitude modulation, in pa rticular the frequency modulation shape of the syllable. This structure is repeated through the different syllables of the call giving a distinct voca l signature. Our experiments also show that the receiver needs to perceive only a small part of the signal: the first half of the syllable (0.23 s) an d the first three harmonics were sufficient to elicit recognition. The smal l amount of information necessary to understand the message, the high redun dancy in the time and frequency domains and the almost infinite possibiliti es of coding provided by the frequency modulation signature permit the chic k to recognize the adult, without the help of a nest site. For these reason s, the code used in the call of the king penguin can be regarded as a funct ional code, increasing the possibility of individual recognition in an acou stically constraining environment. (C) 1999 The Association for the Study o f Animal Behaviour.