Thursday, July 18, 2024

Brown creepers are brown with light spots, resembling a piece of bark. (Photo: Tom Murray)

Although a creeper sounds like it might be a type of spreading vine, a strange, inappropriate person, a green Minecraft exploding mob or a DC comics superhero – or even a monster that comes out every 23rd spring – our local creeper is in fact a brown songbird. Like a Lorax, it is a friend of trees and not creepy at all.

These birds have acquired the moniker because of how they creep up the trunks of trees. According to ornithologist Edward Howe Forbush, a brown creeper (Certhia americana) “winds his way in a preoccupied, near-sighted manner up a tree trunk. Having finally reached the top of his spiral staircase … he drops off to the base of the nearest tree and resumes his never-ending task.” Forbush reports that in one hour, a brown creeper “inspected forty-three trees” and “progressed only about one hundred yards.”

A brown creeper extends its tongue to capture a mayfly on March 31. (Photo: Tom Murray)

Despite the fact that they are most often on clearly visible tree trunks, brown creepers are not easy to spot. Their dull brown color blends seamlessly into the trunk as they hug the bark, and they are often hidden in plain sight. Unlike nuthatches that walk down trees headfirst, creepers walk up and around trees. They cling to the bark with their long claws, probing with their curved needlelike beak into crevices looking for insect eggs, spiders, stinkbugs, fruit flies, aphids, caterpillars, ants, moths, mayflies and beetles. After they have progressed upward, near the top of the tree, they fly down with a fluttering motion that makes them look like a dead leaf falling to the base of another tree. Brown creepers prefer large trees with deep bark furrows where the greatest number of bark-dwelling creatures are found.

Brown creepers can be difficult to spot because they blend in with the bark. (Photo: Richard George)

Most songbirds build nests in tree branches; brown creepers build nests under loose slabs of bark that have pulled away from tree trunks. It sounds as if these nests would be easy to spot, but like the bird itself, the nests blend in. The female spends a week to a month building the nest. She lines it with feathers and bark. Often the nest is a hammocklike structure attached to the bark but not to the trunk itself.

Brown creepers’ long claws help them climb up trees – even upside down! (Photo: Tom Murray)

Ornithologist William Brewster in the fall of 1879 published his description of the nest-building process of a brown creeper. He reported that a tall, dead fir tree had a piece of bark in the process of detaching. The upper edge of the bark was still fastened to the tree, but the lower part had pulled away. Within this space “the cunning little architect had constructed her nest.” The creeper first filled the opening with a mass of slender twigs. On the twigs, she constructed the nest out of “the fine inner bark of several trees.” The shape of the nest conformed to the space in which it was constructed, but “the two ends of the nest were carried upward to a height of several inches above the middle of the nest … which gave to the whole somewhat the shape of a crescent. In the center of the lowest sag … was the depression for the reception of the eggs – an exceedingly neat cup-shaped hollow, bordered by soft bark and lined with feathers from ducks and other wild birds.” Brewster reports that if the space between the bark and the trunk was very narrow, “the foundation of sticks was entirely disposed with, the nest being then entirely composed of bark.” 

A brown creeper finds a morsel in Huron Village in January 2022. (Photo: Richard George)

Given her penchant for building under flaps of wood, you will probably not be surprised to learn that female creepers will sometimes build nests under roof shingles, window shutters or rain gutters. Once the nest is built, the female lays four or five eggs, which she incubates for about two weeks. The males brings her food during this period. The chicks are helpless when they hatch. The female keeps them warm in cold weather, and both parents bring the chicks small insects to eat. Adult creepers are about 5 inches in length if you include the 2.5-inch tail, and weigh only a quarter of an ounce. (For reference: A human eye weighs a quarter of an ounce and an empty soda can weighs half an ounce.)  So you can image how little the chicks weigh. After about two weeks, the chicks fly from the nest, but the parents continue to feed them for another couple of weeks.

A brown creeper climbs a tree in North Cambridge in October 2022. (Photo: Richard George)

After the breeding season, far-north Canadian creepers migrate south; more southern birds, such as our New England creepers, do not migrate at all, but remain here all year long. You are likely to spot the greatest number of creepers in the fall because the Canadian birds migrate south and commingle with our year-round residents for a time. Then the Canadian birds resume their journey to warmer southern climes.

Brown creeper populations appear to be slowly increasing. As agriculture declined in the state in the 1900s, forests reclaimed these fallow lands. Brown creeper ranges expanded as forests regrew.

A brown creeper investigates a knot in a tree in March 2022. (Photo: Tom Murray)

Because brown creepers spend their days climbing tree after tree looking for insect pests, they help control populations that can damage trees. According to scientist Dayton Stone (1932), “Most of the insects taken are highly destructive; and many of them and their eggs … are so small as to be overlooked by the majority of arboreal birds. That this bird is a valuable ally of the forest and horticulturist cannot be doubted.” 

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Seen nearby

David spotted this orange-crowned warbler on Boston’s Mission Hill on Jan. 8, 2023.

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Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.