Functional characterization of begging calls in Thin-billed Prions Pachyptila belcheri chicks

Chicks beg to solicit food and care from their parents. Previous studies of nocturnally feeding Thin-billed Prions (Pachyptila belcheri) showed that chicks convey information about their condition to their parents by means of begging calls. However, those studies used tape-recorders with a limited recording duration, which precluded the recording of complete nights, so only the first begging sessions per night were analysed. Here we present data on begging call intensities and the acoustic parameters of begging elements obtained using digital voice recorders, which enabled complete nights to be recorded. Chicks used from one to five begging sessions per night. We found that the parameters of the first calling sessions did not reflect body condition, whereas the duration of begging sessions and the number of begging calls over the whole night was correlated with the chicks' body condition and the sizes of the meals delivered by the parents. The acoustic parameters of begging call elements were not correlated with body condition. Chicks did not change call frequencies according to their state of nutrition. All call parameters, including the acoustic parameters of chick begging calls, were highly chick-specific. We further tested for age effects and found strong correlations between call features and the age of chicks. The results of the present study show that some begging parameters, e.g. the duration of begging sessions and the number of begging calls over the whole night, are connected with condition, while others, such as acoustic parameters, are linked with individual chick recognition.