Name: Mary Jane S.
Goldfinches are drably colored now, but I know that in a
month or so the males will be bright yellow. How does this happen? Do
they lose their old feathers and grow new ones? Or do darker pigments go
away, leaving the yellow to show through (like autumn leaves)? Or perhaps
outside feathers fall off, and yellow ones are underneath?
It is called molting, old feathers are shed and new ones grow. All birds molt, usually twice
a year in spring and fall. Some species change colors dramatically during molts, some less so,
and some, like cardinals, not at all, but even those you can tell when they have molted as the
new feathers in spring, have a "brighter" look. Most species lose the feathers a few at a time
over several weeks, but mallards, for example, lose enough of their flight feathers at once
that they cannot fly for a short period in late summer.
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Update: June 2012