Over Labor Day weekend we enjoyed the glorious blue-sky days by visiting a few of Maine’s spectacular state parks and other places. Along with gorgeous views, we were struck by the fact that at virtually every stop we made we encountered a hairy woodpecker. It is true that a hairy woodpecker is considered a generally common and widespread bird, and we have seen thousands of them over the years. But despite that, it is not a species like a robin or goldfinch, which you might expect to find everywhere you visit on a particular day.

Most birders know the hairy woodpecker very well. It is a black and white woodpecker roughly the size of a robin (if you can imagine a robin hitching up a tree trunk instead of hopping on the lawn). It is most often confused with its amazingly similar in appearance but sparrow-sized twin, the downy woodpecker. Both hairy and downy woodpeckers were among the earliest North American birds formally described by science. In fact, famed old Linnaeus himself described them in a 1766 publication based on descriptions and illustrations published by the early naturalist explorer Mark Catesby in 1754. Catesby felt that the feathers in the white back stripe on the hairy woodpecker were longer and more hair-like than those in the white back stripe of the downy woodpecker. It seems a bit odd to us today that he focused on such a hard-to-see and seemingly inconsequential feature. Back in those times, though, bird species were being described based on specimens in the hand, and people like Catesby were trying to decipher the animals and plants without any prior knowledge—he was, you might say, developing the first field guides so others could begin to learn what was here and how to species them apart.

Until recently, ornithologists assumed that since hairy and downy woodpeckers look like twins except for their size, they were closely related. Recent genetics-based research has blown that idea out of the water. In fact, hairy and downy woodpeckers are not sibling species at all but are from different branches of the woodpecker family tree. They look alike because of convergent evolution in which similar natural selection pressures over millennia caused them to end up having an incredibly look-alike appearance if not size.

Hairy and downy woodpeckers both occur over most of the U.S. and the southern half of Canada. Hairy woodpeckers (but not downy woodpeckers) are also found in the mountains of Mexico and Central America as far south as Panama and on some of the islands of the Bahamas. Most birders don’t think of hairy woodpeckers as being rare anywhere but they are in the southern two-thirds of Florida—rare enough that we recently submitted photos and video to eBird to document one that we found in the Withlacoochee State Forest of Florida last year.

Both hairy and downy woodpeckers are generally considered resident, non-migratory species. However, occasional fairly large movements of both species have been detected in fall, especially at migration monitoring stations and hotspots. These may not be true migrations in which the birds move south and then north again back to where they originated but instead may be dispersal movements of young birds prospecting for new territories where they will begin their lives as breeders the following spring.

Perhaps the seemingly higher than normal numbers of hairy woodpeckers that we encountered over the weekend are a sign that one of these larger than normal dispersal events is underway. Or maybe it was just a lucky coincidence. Either way, we will keep on looking for those “hairy” feathers that Mark Catesby saw when he first described the hairy woodpecker.

Jeffrey V. Wells, Ph.D., is a Fellow of the Cornell Lab of Ornithology. 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 book, “Maine’s Favorite Birds.”