Development of Parent-Young Interaction in Asynchronously Hatched Broods of Altricial Birds

Abstract

In bird species which have developed a brood reduction strategy, initial inequality among siblings is established through asynchronous hatching. After hatching, the maintenance of a weight hierarchy within the brood and its spread is governed by the allocation of feeds to the chicks and by the rate of parental feeding. In the present study, the initiation of parental feeding and subsequent changes in the feeding procedure were studied in asynchronously hatched broods of the great tit Parus major and the blackbird Turdus merula. During the period of hatching the brood was roused by a parental feeding call on most visits to the nest which made feeding niore effective. Late-hatched young initially increased their chances to receive feeding offers by showing a high rate of spontaneous begging. In addition, they were more dependent than the older young on a high rate of mobility in order to be fed and they showed increasing mobility with age. Crucial changes in the feeding procedure took place at the end of the hatching period when the parents ceased to emit feeding calls and in the last few days before the abandonment of the nest when the biggest young started to jump towards the parents at feeding. These periods were identified as critical for late-hatched young. We argue that parental feeding rate is a feature of parent-young interaction that develops in order to adapt parental investment in individual nestlings to changes in food conditions when the brood is being raised. (Less)