Nestling Call Modification During Early Development in a Colonial Passerine

Nestling calls play a major role in parent-offspring interactions, especially as recognition signals or as signals of need. However, nestling birds undergo developmental changes that are likely to influence their vocalizations. In this study, we investigated changes in Spanish sparrows Passer hispaniolensis nestling calls during the period between hatching and fledgling, and attempted to identify the specific call features associated with the changes. We recorded the calls of nine individual nestlings at 2 (n = 8), 4 (n = 9), 6 (n = 9), 8 (n = 8) and 10 (n = 5) days old. Nestling calls changed substantially during early development, with individual calls becoming less variable. Discriminant function analysis revealed that it was possible to discriminate among and correctly classify calls given by particular individuals at different ages. The most important variables were call duration, harmonious time and maximum frequency. Intra-individual similarities were always greater than inter-individual similarities. However, the calls of different individuals could only be correctly classified in the older age class. These results demonstrate that nestling calls undergo considerable changes during development and suggest that a multi-parametric signal would be a more reliable means of signalling identity or need than a single call parameter.