Blue jays are among the Maine bird species that occasionally experience total baldness on their heads as part of the molting process. Credit: Courtesy of Bob Duchesne

I am often asked where I find the inspiration to write a birding column every week. Sometimes, the inspiration just hits me while I’m sitting on the deck, like when a bald blue jay showed up at my feeder last week.

At least once a year, an alert reader sends me a photo of a cardinal that has lost all the feathers on its head. About half the senders recognize that it’s a bald cardinal. The other half wonders what this black-headed red bird is. It’s an unusual, but not rare, occurrence.

Typically, birds molt their feathers a few at a time. But total baldness happens occasionally, especially with cardinals and jays.

The chief function of the body’s outside covering is to keep the insides in. Whether it’s feathers, fur, scales or your own skin, the top layer of a creature’s body is comprised of dead cells. As these layers rub up against the world, they wear out and need replacement. The process by which birds replace their feathers is called molting. From there, it gets complicated.

Every species has its own molting strategy, determined by Mother Nature. Birds that chase prey, and birds that are prey, need to retain full flight capability while replacing feathers. They replace feathers a few at a time over a longer period.

Other birds, such as large waterfowl, have the luxury of replacing more of their feathers over a shorter period. They may even go flightless for a while. Geese and swans are unable to fly for up to six weeks.

Feather replacement is energy intensive. Large raptors can’t afford the stamina cost of constantly replacing big flight feathers. Eagles retain theirs as long as possible, replacing them only as needed over multiple years.

Molting usually takes place when the bird isn’t engaged in other high-energy functions, such as egg-laying, chick-rearing and migration. Birds often get a fresh set of feathers just before migrating, replacing feathers worn from the breeding season, or post-migration in the tropics when life is more leisurely. Tree swallows start molting in Maine, pause their feather replacement while they migrate, and finish the job down south.

The frequency of molts varies by species. Some molt only once per year, including your own backyard chickadees. Likewise for woodpeckers, jays, flycatchers, hawks and hummingbirds.

Some birds do a complete molt once per year after nesting, then a partial molt before the next nesting season. Often, the post-nesting molt lets the bird change into more drab colors, which attract less attention from predators at a time when the males are not seeking affection. The partial molt before nesting season lets males regain their bright plumage just in time for wooing. American goldfinches are famous for this, but it’s also a strategy used by most brightly colored songbirds, including warblers.

A few species do a full molt twice a year. These are birds that typically rub up against their habitat more forcefully. Grassland species like bobolinks get abraded while pushing their way through the grasses. Marsh wrens suffer the same fate among the sedges.

Some plumage changes are unrelated to molting. Snow buntings molt into fresh brown feathers in fall for better camouflage against the patchy earth and stubble fields on their wintering grounds, including Maine’s blueberry barrens. By spring, abrasion wears off the winter colors, exposing mostly white breeding plumage before flying northward. The wing and tail feathers remain black due to melanin, a pigment that stiffens them for migration. Their otherwise snow-white plumage helps males attract mates when they reach their snowfield nesting grounds.

Many species go through different plumages before reaching maturity. They’ll challenge your identification skills. Herring gulls are particularly annoying, as they take four years to reach adult plumage. Bald eagles take five years to reach breeding age, and their plumage changes every year during their adolescence. Smaller birds can also befuddle observers. Male American redstarts look like females until the autumn of their second year.

Baby songbirds often follow a camouflage strategy. As they grow their first feathers, their body plumage may be much streakier than their parents, affording them an extra measure of concealment. They will replace these feathers before migrating. But they can’t afford the energy cost of replacing the wing and tail feathers, so these original feathers will remain to carry them south.

Good news. My bald blue jay is at the feeder again this morning. Either he’s growing some head feathers back, or it’s an excellent combover.

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Bob Duchesne, Good Birding

Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at mainebirdingtrail.com. He can be reached at duchesne@midmaine.com.