Sexual differences in the control of postnuptial moult in the pied flycatcher

Abstract

In this experimental study, the postnuptial moult in the pied flycatcher,Ficedula hypoleuca, was studied in relation to the timing of the breeding cycle. By exchanging clutches with different laying dates, I either delayed or advanced the breeding cycle. At fledging time, the majority of delayed females started moulting while still feeding the nestlings, while advanced females only rarely did so. The moult of delayed females had also progressed further than that of females in control and advanced groups, respectively. The moult of males had usually progressed further than that of females, but when it started in relation to the breeding cycle did not differ between the study groups. These results suggest that female pied flycatchers have a more fixed timetable for reproduction and moult than males do. The start of moult in females seemed to depend on their original breeding cycle, while the males initiated their moult when the foster brood reached a certain age. A change in the incubation period for females did not affect the hatching success of eggs, but delayed breeding, and extensive moult–breeding overlap imposed fitness costs in terms of fewer fledged young, both absolutely and in relation to clutch size. These findings suggest sexual differences in the mechanisms controlling allocation of resources to reproductive and somatic investments, respectively.