The interplay between flight feather moult and fuelling in Eastern European great snipes Gallinago media

The great snipe Gallinago media, as a long-distant migrant wintering in Africa, faces the challenge of accumulating sufficient energy reserves before departing from European breeding grounds. Despite possible trade-offs in resource allocation, this species additionally initiates moult of flight feathers before southward migration. Here, we discuss the strategy of flight feather moult and fuelling for female and male great snipes from the Eastern European lowland population, exploring their scheduling constrained by the timing of breeding and departure. We found significant intersexual differences in both moult initiation date and the speed of moult. Males start flight feather replacement more than 2 weeks earlier and moult at a faster rate compared to females. However, neither sex completed this process on breeding grounds before the migration, as late in the season all males and half of the females had suspended their primary moult, with the remaining females not moulted at all. Moult of secondaries rarely occurred in the studied population. We observed non-linear energetic stores gain in the studied period, where both sexes maintained stable and low energy stores until the end of July, coinciding with the primary moulting period. Subsequently, there was an increase in energy stores of approximately 1% of the lean body mass per day, indicating a shift towards fuelling for migratory flight. The overlap between stages of stable and low energy stores and moulting suggests a resource allocation towards feather growth before initiating fuelling. Besides limiting a trade-off in resource allocation, this strategy may also contribute to minimizing predation risk, as both increased body mass and missing flight feathers may impair flight. Our study describes moult strategy in great snipe conducted on their breeding grounds, highlighting intersexual differences likely resulting from different parental duties of males and females of this lekking species.