Relationship between moult and migration

Whatever the annual sequence, moult is scheduled in most small and medium-sized bird species in such a way that no migrant has to fly with large gaps in its wings (Stresemann & Stresemann 1966, Payne 1972). The extent to which moult is completed before autumn departure may depend directly on the time available between the end of breeding and the start of migration (Berthold & Querner 1982a). While most passerines migrate only with fully grown flight feathers, birds that are under pressure to leave before conditions deteriorate sometimes start autumn migration before completing their moult (for Greater Whitethroat Sylvia communis see Hall & Fransson 2001, for Rose-breasted Grosbeak Pheucticus ludo-vicianus see Cannell et al. 1983). This applies particularly to late-moulting individuals (Chapter 12). Among many bird species, the juveniles replace only their body plumage, and not their flight and tail feathers, before autumn migration. Again, juveniles often start migration before their body moult has finished, especially those moulting late in the season (for examples see Ginn & Melville 1983).

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