Molting, the replacement of all or some of a bird’s feathers, occurs in response to a mixture of hormonal changes brought about by seasonal changes. This process serves to replace worn feathers (they cannot repair themselves) and can play a part in seasonal camouflage as well as attracting a mate.
All of our small songbirds have a complete molt, replacing all of their feathers in late summer. In addition, many species have a partial molt (replacing body feathers but not wing or tail feathers) in the spring.
According to David Sibley, American Goldfinches begin to molt all of their (alternate/breeding plumage) feathers in September, with the males replacing their brilliant gold feathers with much duller feathers by November. Come spring and the breeding season, male goldfinches replace their dull (basic/non-breeding) body feathers (but not the wing or tail feathers) with new, bright feathers.
Imagine my surprise when I spied a brilliantly colored American Goldfinch at my feeder this week. According to ornithologist George Clark, it’s usually March before one starts to see an American Goldfinch in breeding plumage. One can only wonder what prevented this individual from molting its breeding plumage in the fall. (Photo: male American Goldfinch, winter plumage; inset – male American Goldfinch in breeding plumage in January)
Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.