The results of the Vineyard’s Least Conspicuous Songbird Contest are in, and they’re unanimous: The brown creeper, Certhia americana, is the undisputed champion.
Tiny at about five inches in length, the brown creeper spends most of its time clinging to the bark of trees, often hitching upward along the trunk. Its behavior while doing so is slow and deliberate. And the plumage of a brown creeper, mottled brown on the head, back, wings, and tail, blends in well with the irregularities and brown color of tree bark. Coloration and behavior make this species infuriatingly hard to detect by visual means.
A creeper’s vocalizations are not much help to a birder. These birds rarely have much to say while foraging. The song, which is fairly loud and carries well, is a series of about four short, whistled notes, generally descending slightly in pitch. But this song is tuned to a very high frequency, in the range at which human ears start to lose their sensitivity. Indeed, a common complaint among aging birders is that they have lost the ability to hear brown creeper songs altogether. The typical call note of this species, a simple, lisping “tseep” note, is even higher in pitch, and correspondingly harder to hear.
If we held a contest for Most Unusual Songbird, well, the creeper would win that one, too. The species is the only member of its family that occurs in the Americas, and that family, Certhiidae, is a small one, with just nine species in a single genus. This means that the brown creeper is only a distant relative of all the other songbirds on our continent.
One might be excused for thinking that the brown creeper is a species assembled from spare parts borrowed from other birds. Anatomically, the creeper is highly evolved for its arboreal explorations, and shares one curious adaptation with the woodpeckers, which are essentially unrelated. Both have evolved stiff, pointed tail feathers, which, as the owner of those feathers creeps upward along a tree trunk, snag on the bark and offer support.
While the feet of creepers and woodpeckers differ, again, there is a functional similarity. On a woodpecker foot, two toes point forward and two backward, allowing for a clamplike grip on tree bark. A creeper has the conventional songbird arrangement of three toes pointing forward and one pointing back. But that backward-pointing toe is a corker, robust and elongated. Matched with the sharply clawed, forward-pointing toes, that rear toe serves the same supportive function as the rear pair of toes on a woodpecker.
In terms of behavior, the brown creeper most closely resembles the nuthatches, similar to the creeper in small size and arboreal habits. But in contrast to the creeper’s penchant for climbing upward along a trunk, nuthatches are famous for clambering downward, headfirst, along a trunk as they forage. During migration, especially in the fall, brown creepers and red-breasted nuthatches often turn up in the same places, either traveling together or zeroing in on the same resources.
Creepers forage as they creep, taking virtually all their food in the form of insects, spiders, and eggs and larvae gleaned from tree bark. The thin, downturned bill of a brown creeper is perfectly suited for this myopic foraging strategy. By both behavior and anatomy, this curious bird is optimized for picking tree trunks clean of insect life.
Overall, brown creepers nest in forested habitat from Central America north into Southern Canada, north along the coasts to Alaska and the Maritime Provinces. The species is notably scarce in the prairie states, reflecting the shortage there of extensive tree cover. Breeding bird surveys suggest that brown creepers are increasing in Massachusetts, probably as a result of reforestation.
I’m a bit obsessed about brown creepers just now because one has been singing every day outside my office off Lambert’s Cove Road. This persistence indicates a territorial male, either hoping for a mate or perhaps already mated, and looking around, it is easy to see why this bird has set up shop.
The woodland around our office is one of the increasing number of areas on the Vineyard in which pitch pines have succumbed to invasion by Southern pine beetles. As the dead pitch pines begin to break down, large flakes of bark are beginning to peel off. And the brown creeper stands to be a beneficiary of this process.
The favorite nesting site of a brown creeper is behind such a flake of loosened bark, where the female creeper suspends a nest made of twigs, grass, and feathers. Brown creepers have always nested on the Vineyard, in irregular numbers and in unpredictable locations. But one consequence of the Southern pine beetle invasion will likely be a huge increase in nesting opportunities for brown creepers. Look for this odd and elegant bird to show at least a short-term growth in breeding numbers over coming seasons.