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Dull or colorless plumage that certain birds, such as male ducks, acquire at the end of the breeding season.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
(Zoology) seasonal plumage that occurs in certain birds after the breeding plumage and before the winter plumage: characterized by dull coloration
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014