Annual variation in the timing of breeding and moulting in male and femalePied Flycatchers Ficedula hypoleuca

During five breeding seasons, the timing of breeding and moulting was studi ed in the Pied Flycatcher Ficedula hypoleuca. In central Sweden, on average 67% of the males and 41% of the females started moulting before the young fledged. The proportion of individuals with an overlap between breeding and moulting varied considerably between years, with the highest proportion of moulting males being recorded in the year when the females started egg-lay ing on the latest date. Despite a large annual variation in the proportion of individuals showing a moult/breeding overlap, the duration of this overl ap varied insignificantly between years. The onset of moult in males seemed to be related to; both calendar date and timing of the current breeding at tempt. Most females postponed their moult until just before or just after t he fledging of their young, independent of calendar date. There was no sign ificant relationship between male and female moult scores and nestling weig ht at fledging or fledging success of their brood. Thus, in long-distance m igrants such as Pied Flycatchers, it may be adaptive to have some overlap b etween reproduction and moult, but there seems to be a limit to how early i n the breeding cycle they are able to start moulting.