Reproductive synchrony in the fieldfare (Turdus pilaris) in relation to spring arrival,nest predation and nestling starvation

Summary In SW Sweden, solitary fieldfares (Turdus pilaris) were synchronized to the same degree as those living in colonies. In N Sweden, I investigated the degree of synchronization among colonies of varying size because solitary breeding occurred only occasionally. The degree of synchronization was not related to colony size. Synchronization was strongest in years when breeding started late and weakest in years when breeding commenced early. In N Sweden, the nest predation risk increased slightly as the season progressed. In SW Sweden, nestling mortality due to starvation was highest in early breeders, but their fledgling production exceeded that of late breeders. Increased nest predation penalized late layers.