Unusual pattern of skipped or shortened moulting of flight feathers in late-breeding Common Shelducks

Experimental studies have shown that individual wildfowl can shorten or skip moulting if the time between breeding and wintering is short; however, studies in wild birds are scarce. We tracked nine Common Shelducks Tadorna tadorna during the breeding and moulting seasons and determined the flightless time during moulting based on typical movement patterns. We found different movement patterns for two late-breeding females, suggesting that they skipped or shortened the moult of their flight feathers. These results provide a link between previous experimental studies and the situation in wild birds, likely reflecting an individual trade-off between the times allocated to moulting and breeding, respectively.