In mid-February, I saw a bird for the first time on Seabrook Island – an Indigo Bunting. I didn’t recognize it initially with it’s brown plumage with just a hint of blue. After about a week, it disappeared to return mid-March. Boy, what a difference now that he was in his breeding plumage. The pictures were taken through a window but they still clearly show the difference.
I know several “Yankees” who didn’t initially recognize our wintering American Goldfinch in their drab plumage. About the same time as my Indigo Bunting returned, I saw an American Goldfinch in his summer finery. These changes caused me to research more about molting. The Cornell Lab’s All About Birds site provided an excellent article: The Basics: Feather Molt. The first few paragraphs answered a lot of my questions:
A feather is a “dead” structure, analogous to hair or nails in humans and made of the same basic ingredient, the protein keratin. This means that when they get damaged, feathers can’t heal themselves—they have to be completely replaced. This replacement of all or some of the feathers is called molt. In addition to providing a new set of healthy feathers, molts often provide a new look to the bird’s plumage—new colors or patterns that can indicate the bird’s age, sex, or the season of the year.
Molt is extremely variable. Observed patterns can vary by species, by individual, from year to year, and by individual feathers on the same bird. Molts can be either complete, in which the bird replaces every one of its feathers over the same molt period; or partial, in which the bird replaces only some of its feathers (for example, flight feathers or body feathers).
Molt keeps birds in top flying condition by replacing feathers that have become worn or damaged with completely new feathers. However, if a bird loses an entire feather, that feather will begin growing back immediately rather than waiting for the next molt. (This is why people clip the flight feathers of captive birds rather than plucking them out.)
Molting occurs in response to a mixture of hormonal changes brought about by seasonal changes. The entire process is complex and many questions remain regarding how the process is controlled. A basic understanding of molting patterns can be a useful aid in identifying many species and in determining their age.
It takes a lot of energy to build new feathers. As a result, timing is important—and birds typically time their molts to avoid other periods of high energy demands, such as nesting or migration. Molt timing can be more complicated for larger birds, because growing larger feathers means that their molt process takes longer than it does for smaller birds. This is one reason why some birds undergo partial molts.
I encourage you to read more about this feature of our feathered friends but reading the entire article The Basics: Feather Molt by Cornell Lab’s All About Birds.
Submitted by: Judy Morr
“Did you know” is an on-going series of blogs that answer possibly more technical questions people have about birds or their environments. If you have an idea or question, submit it via the “Ask SIB” link on the SeabrookIslandBirders.org web site or send an email to SeabrookIslandBirders@Gmail.com.
One thought on “Did you know: Birds molt changing their appearance”
Very informative piece, Judy. Missing my winter birding. Very light snowfall here this year.