Effects of latitude on the trade-off between reproduction and moult: a long-term study with pied flycatcher

Long-distance migratory passerine birds are generally time constrained by r eproduction and moult, which need to be completed before migration. Breedin g and post-nuptial moult may overlap especially under time-constrained cond itions (northern latitudes). Here, we analysed the timing of adult moult in relation to latitude, timing of breeding and reproductive effort in pied f lycatchers (Ficedula hypoleuca) breeding in four widely separated populatio ns (40-68 degrees N). In males but not females, the proportion of moulting birds while provisioning nestlings increased with increasing latitude. This may suggest that a moult-breeding overlap is a strategy employed by male p ied flycatchers to adjust to the short breeding season at northern latitude s. However, the moult-breeding overlap was more pronounced among males in t he southernmost study population (Spain). In this population, males may dec ide not to invest more in reproduction, and start moulting at earlier breed ing stage than in northern populations,or, alternatively, birds in the Medi terranean region are time constrained by the hot and dry summer. The trade- off between breeding and postnuptial moult may be more important in some po pulations than in others, depending on the latitude of the breeding site. O ur results show that a moult-breeding overlap imposes a fitness cost on mal es in terms of fecundity and breeding success.