The Outside Story: Denizens of the bark

May 1, 2021 | By Lee Emmons

On certain afternoons if I time it just right, I may spot a brown creeper on the trunk of a tree in my front yard. Moving stealthily, almost imperceptibly up the tree, the brown creeper hunts for food amongst the bark. I watch this avian mission with a sense of appreciation, as the bird flies to other trees to repeat the process.  

Brown creeper illustration by Adelaide Murphy Tyrol

These inconspicuous birds known as Certhia americana are denizens of the bark, creeping their way through the world largely unseen by human eyes. Even while watching closely, it is easy to lose sight of a brown creeper as it blends into the bark, nearly perfectly matching the tree’s coloring.

Brown creepers are about five inches long, with a wingspan of seven inches. They have long, stiff tails which they use to prop themselves against tree trunks as they climb and forage. They use their long, downward-curving bills to probe for food.

In his book, “What It’s Like to Be a Bird,” David Allen Sibley noted, “Even more than woodpeckers, creepers hug the bark, staying very close to the tree and leaning in to peer under bark scales and into furrows, then using their long curved and pointed bill to extract tiny spiders, insects, and eggs.”

Occasional visitors to backyard suet feeders, brown creepers primarily feed on a variety of natural foods including spiders, beetles, ants, moths, stink bugs, and caterpillars. Unlike nuthatches, brown creepers do not descend trees while foraging. Moving from one tree to another, these hard-to-spot birds instead spiral upwards in search of a meal. Occasionally, brown creepers may also feed on the ground.

Brown creepers are year-round residents of New York and northern New England, and their range also includes Alaska, the western United States, and parts of Canada and Mexico. Data from U.S. Fish and Wildlife banding records indicate that some creepers from the northern extent of the range may migrate as far as 500 miles in mid-autumn, returning to breeding grounds in early spring. 

Others are local migrants, travelling only a few miles. Typical habitat includes both hardwood and coniferous forests. Orchards, public parks, and backyards with suitably large trees provide shelter during the winter.

Brown creepers nest primarily in dead trees, where they tuck their cup-shaped nests under peeling bark or into snags. As noted in “Birds of Maine,” they may also build nests on human structures such as window shutters and rain gutters. Nests are located at varying heights but are normally situated more than a few feet off the ground. The female constructs the nest from moss, bark, lichens, leaves, and hair. 

Females typically lay five or six eggs and incubate these for about 15 days. The male provides food during this time. Nestlings remain in the nest for two to three weeks and are fed by both parents. Brown creepers have only one brood per year, and mated pairs may separate after the breeding season. Less territorial in the winter than during other parts of the year, brown creepers may gather in roosting groups and sometimes feed with other species.

According to the Cornell Lab of Ornithology, forest fragmentation and the removal of dead trees threaten brown creepers. In addition to the loss of these potential nest locations, the cutting of living trees removes feeding sites. However, in New England, the regeneration of forests and the creation of new snags may have helped increase creeper numbers.

At over nine million birds, the breeding population of brown creepers in North America is considered stable or increasing. To help conserve this species, woodlot owners may leave some snags standing. And if you happen to look at just the right time, you may see a brown creeper working its way up a tree near you. 

As secretive, unobtrusive birds go, brown creepers are playing their part to perfection. 

Lee Emmons is a nature writer Newcastle, Maine. The Outside Story is assigned and edited by Northern Woodlands magazine and sponsored by the Wellborn Ecology Fund of the New Hampshire Charitable Foundation.