Of a Different Nature: Molt and Bolt
by Michele L. Tremblay

September 2013

“Where did the summer go?” is a popular lament at this time of year but with it, one might add, “Where did the birds go?”

In the spring, the dawn chorus of bird songs is impossible to miss. There is a seemingly non-stop and joyous cacophony of singing from many birds returning from southern habitats as well as those still here after a long, cold winter. In the early summer, one can see birds nearly all day long—from dawn through dusk—visiting feeders, flying through trees, and walking on the ground seeking food. Sometime in late July or early August, it gets quiet and the chorus of birds is supplanted by the buzzing of insects. It is eerily quiet and feels almost as if nature is holding its breath. Where did the birds go?

The songbirds and waterfowl are still here but are undergoing a molt of their feathers. After the intensity of breeding season, birds begin their molting season where they lose tattered feathers worn from sunlight, grooming, abrasion, and use in flying, swimming, or otherwise moving around. Some birds may also need a new coat with insulating downy feathers to keep them warm in the coming winter. Amazingly, birds will lose all of their feathers—although some species will lose them all at the same time—and replace them completely before fall.

Songbirds may look motley or a bit odd during this time. For instance, the bright yellow and black American Goldfinch males look a bit less dapper and are starting to appear more like females or their winter selves with olive and black plumage. Other birds have a mix of old and new feathers. Vibrant and beautiful Blue Jays with their jaunty caps may be balding slightly (or a lot).

Some waterfowl, such as loons and grebes, lose all of their feathers at the same time

“There are quite a number of ducks that cannot fly during the summer,” said Becky Suomala, a Biologist with New Hampshire Audubon, “During this flightless period, brightly colored Mallard and Wood Duck males look nothing like do with their usual gorgeous male plumage.” The dun colored appearance is called, “eclipse plumage.” During this time, birdwatchers often ask where all the males have gone because they look more like females during this period. Their colors become plainer so that they can hide from predators more easily while they are grounded.

This inconvenient truth for birds is a necessity. Feathers provide not only the ability to fly but also to keep birds cool or warm as well as dry. Like human hair or fingernails, feathers are formed by the keratin, a protein. Damaged feathers cannot heal and must be shed, or molted, and then replaced. Molting is timed in response to birds’ hormones and seasonal changes. While the exact science of the timing is not understood fully, fortunately, it does not coincide with migration, mating, or the rearing of young.

Understandably, molting makes it difficult for birds to get around easily and puts them at a disadvantage with predators. During the molt, birds often become reclusive and do not vocalize as much as they did in the spring and early summer. This is so that they do not attract attention to themselves. They do a fair job of it—it becomes less common to see some of the more vulnerable small songbirds such as sparrows and warblers, and grounded waterfowl during their molting period.

Some birders take a break from seeking and watching avian friends during this time. When birds are seen looking worn and vulnerable, many people are concerned that “their birds” are sick or dying. Not to worry: The late summer molt is merely a small moment in birds’ lives and prepares them for another harsh New Hampshire winter or a long and perilous journey to a warm and tropical paradise for a few months.

You can learn more (and have fun) with these selected resources
Cornell Lab of Ornithology molting fact sheet

Stanford University short essay on molting

Balding Blue Jay image



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