Tuesday, February 25, 2014

An Avian Chameleon: The Brown Creeper

Brown Creeper (Wikimedia Photo)The fields and forests of the Adirondacks support many forms of animal life, even during winter, yet many of our wildlife residents are next to impossible to glimpse. Some, like moles, shrews and voles prefer an existence below the surface of the snow, while others such as fisher, bobcat and ermine have adapted a shy and secretive lifestyle causing them to spend nearly all of their time in remote sections of dense woodlands where visibility is limited, making a chance sighting rare. Others, like flying squirrels and owls conduct their affairs under the cover of darkness and seldom are viewed.

One small bird, considered by ornithologists to be widespread throughout the Park year round, is likewise noticed only on rare occasions, despite its regular foraging activities during the light of day. The brown creeper is a slim, chickadee-size bird with mottled brown plumage on its head, back, sides, and tail, which closely resembles the color and pattern of the rough-textured bark that covers many types of mature trees.

When this bird senses the presences of an intruder, it quickly pulls itself against the trunk. This allows the creeper to perfectly blend into the background of bark and causes it to go mostly unnoticed by hikers, campers and nature enthusiasts as they travel through our forests.

The brown creepers gets its name in part, from its habit of creeping up the trunk of sizeable trees. As it does, this bird probes the cracks and crannies in bark with its long, slender and slightly arched bill. Throughout the latter half of summer and for much of early autumn, many insects, spiders and other invertebrates seek out the shelter afforded by the furrowed bark on older trees for their egg clusters, nymphs, larvae or pupas. Like the chickadee and nuthatch, the brown creeper feeds heavily on the bugs that lie dormant in the recesses of a tree’s outer covering.

The high protein and caloric content of overwintering bugs make these items extremely valuable to a small, warm-blooded entity, and over eons of time, the creeper has evolved the technique for locating and extracting these highly nutritious morsels. Despite the harsh weather that occurs for months in our northern climate, the creeper is able to subsist on an invertebrate diet, and in the process help with the control of those bugs that utilize this type of shelter to survive winter.

Like a miniature woodpecker, the creeper has a stiff tail that it uses to push against the trunk to provide the proper leverage for forcing its needle-like bill deep into the small crevices where many invertebrates finally settle before the onset of winter. The legs of the creeper are quite short, which keeps the body of this bird close to the trunk of a tree, making it harder to see as it slowly works its way upward. Unlike the nuthatches, which often work their way down a trunk, or the chickadee which occasionally dangles from the bottom half of a limb, the creeper tends to concentrate its foraging efforts on tree trunks and always works its way upward from the base. Once it reaches the top, this bird simply drops off and flies gently downward to the base of another nearby tree where it repeats the process.

In summer, the brown creeper is known to prefer stands of softwoods, especially those of the pines and hemlock. With the onset of cold weather, the creeper begins to expand its search for food to other sections of forest, particularly those containing wild black cherry and maples. As it prowls the forest for food, it may temporarily join a flock of chickadees, or a pair of nuthatches as they explore similar places for similar food items. The creeper, however, is not known to compete with these other birds, as it targets invertebrates that chickadees are unable to reach, and the dormant bugs that reside under the lower half of a piece of bark, while the nuthatch hunts for those that exist beneath the top portion of a chunk of loose bark.

Because the creeper often remains near other individuals, it occasionally emits a high-pitch, two note call that keeps the birds in contact with one another as they disappear behind the trunk of a tree. This is similar to the vocal contact maintained by the members of a chickadee flock as they forage in areas where they may frequently lose sight of one another. However, the call note of the creeper is simple in composition, rather soft in volume, and easy for a person to overlook when it is repeatedly given by a pair of creepers working a stand of trees.

It is usually not until the latter part of March that the male creeper begins to advertise its presence with its breeding song. However, this is when the song of the winter wren, along with the voices of several other forest denizens, can also begin to be heard, which can make the creeper’s mating call less noticeable.

The brown creeper is not a rare, or unusual species of bird in the Adirondacks, even in winter. However, it typically takes a favorable stroke of luck, or a hike into a forest with a die-hard birder who is well acquainted with its call note to be able to catch a glimpse of this delicate creature responsible for controlling the population of numerous bugs here in the Adirondacks.

Photo courtesy Wikimedia.

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Tom Kalinowski is an avid outdoor enthusiast who taught field biology and ecology at Saranac Lake High School for 33 years. He has written numerous articles on natural history for Adirondack Life, The Conservationist, and Adirondack Explorer magazines and a weekly nature column for the Lake Placid News. In addition, Tom’s books, An Adirondack Almanac, and his most recent work entitled Adirondack Nature Notes, focuses on various events that occur among the region’s flora and fauna during very specific times of the calendar year. He also spends time photographing wildlife. Tom’s pictures have appeared in various publications across the New York State.

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