Birds in Winter
By Noreen O’Brien, Purchasing, Marine Parts Express
Birds are of a marvelous design, just like everything else in the natural world, and have ways of keeping balance in their lives, even during the coldest temperatures of the shortest days of the year. To survive, most birds must maintain a body temperature of about 104 degrees Fahrenheit. To maintain that temperature in the cold of winter, they employ a variety of strategies.
Food being the primary source of energy, and the available winter hours for them to feed being fewer than the hours of sleep, birds must eat almost constantly just to survive. This is a good reason to include a high energy food like raw beef suet at your backyard feeding station throughout the winter months. They need enough daily food intake to draw from stores that will fuel heat created by their own bodies during the nighttime.
Bird feathers have tiny muscles at their base, making it possible to fluff them, thereby trapping an insulating layer of air between their feathers and skin. Do you use a down parka? If you bend over, you’ll note the woosh of warm air trapped under the zipped parka when it escapes under your chin. Same premise holds in the case of birds, but it’s built-in for them. Like us, birds also shiver when they’re cold, as a kind of exercise, which turns the body’s stored fat into heat.
As can sometimes be seen on a cold, sunny day, a bird may sit with its back to the sun, head turned toward its back, face tucked into the plumage of its shoulder. Water birds such as ducks floating on the water’s surface will do this, as well. Such a position decreases the total heat-dissipating area of its body, but it also covers bare surfaces that lose heat, such as facial skin, naked combs or wattles.
Shorebirds, gulls, and waders may be seen standing on one leg on rocks or on the beach, head tucked into a shoulder, body facing into the wind—the other leg is tucked up close to its belly. Birds can control the temperature of their legs and feet separately from their bodies by constricting blood flow to these extremities, thereby reducing heat loss. In addition, their legs and feet are covered with specialized scales that minimize heat loss, also allowing them to conserve heat for the rest of their body.
Birds of open areas have their strategies, too. Wind velocity is greatly diminished at ground level. Birds such as sparrows or larks will scrunch up together, close to the ground, sometimes making a bit of an igloo out of snow or a grass tussock, or by scratching a shallow hollow in the ground’s surface.
To fully protect itself from the cold temperatures, wind, and precipitation through the night, a bird would do well to have a solid wall of cover surrounding it. The more enclosed the bird is, the less heat escapes into the air around it. Most frequently, songbirds roost alone, however, on extremely cold and bad weather nights birds will congregate in huddles, sometimes with groups of different species, but mostly of the same. A British ditty describes this, “When tom-tits cluster, soon it will bluster.”
A collection of Brown Creepers might cling to the bark of a tree trunk in a huddled mass, bodies overlapping, heads inward and tails sticking out. Black-Capped Chickadees and Tufted Titmice generally sleep alone, perhaps snuggled into a bough of a conifer, but on a cold night, these birds may gather in a huddle inside an old woodpecker hole, an old nest of another species, or even a nest box.
The Yellow-Rumped warbler, a hardy warbler that may be found here along the northeastern coast even in winter, is not a colonial or a cavity nester. However, these warblers have been known to seek out others of their species and hunker down in an old nest for added warmth and protection from the harsh elements.
Maine writer Bernd Heinrich released a report not too long ago of a study he made on the wee four-inch kinglets. He spent many cold Maine nights following the birds until he found what he was looking for: kinglets roosting together huddled for warmth and survival.
There is a downside to some of these strategies birds use. Sometimes, when cleaning nest boxes in early spring, carcasses of birds are found inside them. The birds died over the winter from the cold, suffocation from the weight of layered birds with the top ones dying from exposure and the bottom birds too weak to work up through the pile, or starvation.
Still, huddling must work for the birds more often than not or they would not be using such a strategy to survive a cold winter’s night. On cold late afternoons, watch nest boxes for birds like chickadees and nuthatches, and even the occasional woodpecker, entering for the night. Also, look for juncos, sparrows and other small birds roosting in the shrubbery around the house. Better still, hang boxes and plant shrubs next spring with the birds in mind. They need all the help they can get surviving these long Maine winters.
Till next …
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December 12, 2011 / Noreen O'Brien / 0
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