AbrasionWear of the feathers. In cases where the tips are coloured differently from the lower parts of the feathers, abrasion can change the appearance of the plumage quite considerably, and in this way winter plumage can become breeding plumage without the necessity for moult. This 'abrasive moult' is found in many passerine birds, for example the Starling Sturnus vulgaris and the Chaffinch Fringilla coelebs.
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From Peter Weaver's Birdwatcher's Dictionary
Copyright © 1981 by Peter Weaver