It’s that time of year again. Back-to-school shopping for many families. Last-days-of-summer camping trips.

And time for bald birds to begin making appearances.

Although we haven’t seen any ourselves yet this year, the MaineBirds listserve has received posts from people who have been seeing bald birds around their yards. These posts, and the questions they inspire, harken us back to our days at the Cornell Lab of Ornithology, where inquiries about birds with featherless heads ranked high on the list of FAQs from our members and the public.

So, what’s up with bald birds?

They look strange, for one thing—odd reminders that birds are descended from dinosaurs. But baldness in birds is not an infrequent occurrence. Blue Jays and Northern Cardinals tend to “bare” the condition, in particular. Perhaps it was not coincidence that these same two species that were recently reported on the listserve as flaunting their feather-free noggins.

Naturally, people who see bald birds are concerned for them. The two observers who reported their recent sightings to MaineBirds had done their homework and noted that the condition was very likely the result of molting. Indeed, this is the time of year (late summer and into fall) when most birds molt. Typically, this natural phenomenon is not so dramatic; birds shed old, damaged feathers gradually to make way for new ones (which especially come in handy for the long migration many of them are about to launch into from their breeding grounds to the wintering areas).

Molting is triggered by hormonal changes usually brought on by seasonal ones. It makes sense that these in turn are timed to avoid periods in a bird’s life when energy needs are at a premium, like during breeding. There are lots of interesting variations between bird families and species related to how, when, and where they molt. Most waterfowl species have a period in mid- to late-summer when they molt all of the wing weathers at once and become flightless for up to a month. Many other birds molt only one or two of the very vital wing feathers at a time so that they can still fly. Some birds molt before they migrate south in the fall while others migrate upon arrival on the wintering grounds.

None of that, however, answers the question most obviously at hand: Why do some, like those aforementioned, lose their head feathers all at once?

Researchers have yet to provide a definitive answer to that question, but some hypothesize that this sudden glabrous state is tied to nutrition (or lack thereof), environmental factors, parasites such as feather mites, or something completely unknown. Rest assured, the birds are not in pain (even if it pains us to see them this way!), and the feathers will be replaced in a week or so.

While researchers continue to learn ever more about molting—including sudden full-head feather loss in species like Blue Jays and Northern Cardinals—they also provide opportunity for hands-on, or should we say, “eyes-on” learning by the observers themselves. One of the reports to the MaineBirds listserve included this insightful little tidbit: “One of the Blue Jays has shown some growth over the last week, more than the other, anyway. The cardinal…is still very bald. It's also how I learned that cardinals have black skin.”

Yet another example of some of the fascinating things birds, er, “reveal” to us!

Jeffrey V. Wells, Ph.D., is a Fellow of the Cornell Lab of Ornithology and Vice President of Boreal Conservation for National Audubon. Dr. Wells is one of the nation's leading bird experts and conservation biologists and author of the “Birder’s Conservation Handbook.” His grandfather, the late John Chase, was a columnist for the Boothbay Register for many years. Allison Childs Wells, formerly of the Cornell Lab of Ornithology, is a senior director at the Natural Resources Council of Maine, a nonprofit membership organization working statewide to protect the nature of Maine. Both are widely published natural history writers and are the authors of the popular books, “Maine’s Favorite Birds” (Tilbury House) and “Birds of Aruba, Bonaire, and Curaçao: A Site and Field Guide,” (Cornell University Press).