Moult migration is a form of migration seen in some ducks and geese.
It occurs towards the end of the breeding season and sees individuals travel a substantial distance to gather at traditional sites. These sites are selected because they offer food and safety from predators, allowing the birds to replace their flight feathers – a process that leaves them flightless and potentially vulnerable.
In geese, only the non-breeders or those individuals whose breeding attempts have failed make moult migrations.
The selected moulting sites usually lie to the north of the breeding range, which is why we see introduced Canada geese from southern Britain gathering at sites in Scotland.
The moult migrations undertaken by ducks tend to be more variable in terms of the direction flown.
British shelducks, for example, fly east to join thousands of other individuals from elsewhere in western Europe at moulting sites located on the tidal mudflats of Germany’s Wadden Sea.
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Main image: Canada goose. © Dave Porter/ Getty