Hatching asynchrony in Linnets: the effects of nest predation and food demand of nestlings

Abstract

In this paper, we investigate hatching patterns and nestling growth in the Linnet Carduelis cannabina. We evaluate five possible hypotheses to explain the evolution of facultative hatching asynchrony in this species. Both synchronous and asynchronous hatching was observed in the Linnet, with small broods hatching synchronously and large broods hatching mainly asynchronously. Nest predation seemed to cause higher mortality in the late nestling stage compared to the mortality before incubation, which mayexplain the observed synchronous hatching of small broods. Asynchronous hatching resulted in increased weight hierarchies within broods, but was not associated with brood reduction, as implied by the traditional brood reduction hypothesis . Asynchronously hatched young had higher growth rates than synchronous young, indicating the importance of reducing competition between siblings or reducing peak load in food demands by asynchronous hatching when brood sizes were large. This study thus suggests a mixture of two strategies : synchronous hatching to reduce the risk of nest predation when the brood size is small (nest failure hypothesis), and asynchronous hatching to enhance growth conditions of young when the brood size is large (peak load and/or sibling rivalry hypothesis).