Winter World_ The Ingenuity of Animal Survival - Bernd Heinrich [49]
Sitting down on the trunk of a fallen balsam fir, I listen for the light but steady tapping of a black-backed woodpecker. Black-backs come here only in the winter, and sometimes I can hear one. They specialize in feeding on bark-beetle larvae found in recently dead spruce and balsam fir trees. Lightly tapping on the bark as if palpating the tree trunk for possible hollow sounds where a larva might reside, these woodpeckers work like a physician tapping a chest for infirmities. No black-backed woodpecker is near today, but I hear a pileated’s vigorous hammering. The bird is probably excavating a deep vertical groove into the base of a balsam fir trunk to reach the hibernating carpenter ants deep within the core of the tree. It takes brute force and specialized talents for these insect-eating birds to make a living while remaining in these winter woods. One of the insect-eating birds that seems to be without a visible means of support is the golden-crowned kinglet. This spruce-fir grove is where I go most often to try to find them.
Kinglets have thin voices that are barely audible in the human range of hearing, and they are neither seen nor heard unless you really tune in. Golden-crowned kinglets do not eat the seeds of the various trees that sustain the finches that stay here all winter, nor do they eat the plentiful tree buds, like the squirrels and grouse do. They cannot reach grubs under bark or buried deep in wood. Yet they obviously fuel their raging metabolism to keep warm. They hover at the tips of branches, hop nonstop in dense spruce thickets, and pick at seemingly invisible prey.
The kinglets’ tiny bills are suited for gleaning insects from twigs. But what insects could there possibly be about in the winter? How do these gold-crowns manage to find up to three times their own body weight of food each short winter day, as they predictably must to have enough fuel to keep warm? If kinglets are without food for only one or two hours in the daytime, they starve (and freeze) to death. Yet, some of their population clings to the north woods, despite the fifteen-to twenty-hour-long winter nights. Since the birds don’t forage at night, and since they have not been observed to cache or store food in the day, what saves them from dying ten times over during the night?
Is that a conversation of barely audible tsees in the spruce thicket? No doubt about it. Finally I hear it. And they are coming closer. The sounds are as unobtrusive as a gentle breeze, and they just as easily go unnoticed. There among the thick branches, I finally see one of probably several tiny callers hop and hover hummingbird-like near the end of a branch. A kinglet never holds still for more than a second. Nonstop foraging. Try as I might, I cannot see them actually catching and eating anything, even as I get within three or four feet of them on those rare occasions when they came out of the spruce tops. They feed on prey too tiny for me to see.
What kinglets eat in the winter had long been a mystery, and researchers had relied on speculation to try to decipher what food these insectivorous birds might find in the winter. They reasoned, on the basis of anatomy and behavior, that the birds are springtail (Collembola) specialists. A species of these primitive almost microscopic insects commonly known as “snow fleas” (Hypogastrura tooliki, formerly H. nivicola) at times pepper the snow in these New England woods. I have seen millions of them gathering in track depressions in the snow, almost blackening the sides and bottom due to the sheer numbers of individuals. They color the snow gray to almost black, depending on their collective numbers. You see the individuals as almost stationary dots that creep about slowly on tiny stubby legs. But when you look closer, you are apt to see some of them hurtle off and disappear in flealike leaps, hence