Moult migrationA regular movement to and from an area where the birds moult. This type of migration takes place at the end of the breeding season and is found in the Shelduck Tadorna tadorna, of which most breeders in the British Isles fly to the Heligoland Bight, with a smaller number travelling to Bridgwater Bay in Somerset. Presumably the purpose of such migrations is the provision of a safe moulting ground, especially as wildfowl become flightless during the moult.
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From Peter Weaver's Birdwatcher's Dictionary
Copyright © 1981 by Peter Weaver