Wildlife: Metabolism, feathers help birds survive winter nights
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The long, cold winter nights that lie ahead make day-to-day survival a challenge for wild birds. Smaller birds face the greatest problem because they lose heat more rapidly than larger birds.
Wherever a bird sleeps, its first line of defense against cold is its feathers. Feathers repel water and efficiently insulate warm bodies from cold winter air. Each feather is controlled by a group of small muscles that can raise and lower the feather. By fluffing their feathers, birds create many tiny air spaces that increase insulation and reduce heat loss.
On extremely cold nights, birds reduce heat loss further by burying naked body parts into their feathers. This is why birds tuck their bills into their shoulder feathers and why many water birds often sleep with one leg held tightly up against the body.
During the day, birds feed constantly to fuel the metabolic furnace that keeps them warm through the night. Backyard feeders are busiest on the coldest winter days.
Sleeping quarters also protect birds from the elements. Song birds such as cardinals and finches retire to dense thickets of vegetation. Conifers and ivy-covered walls provide even greater protection. Ring-necked pheasants, ruffed grouse, robins and house finches are just a few of the birds that roost in evergreen refuges. This is a good ecological reason every backyard wildlife sanctuary should include some evergreens.
Screech-owls, woodpeckers, titmice and nuthatches sleep in cavities much like the ones in which they nest. As many as a dozen bluebirds sometimes cram into a single nest box or cavity.
Roosting cavities cannot guarantee survival. Sometimes it just gets too cold and birds freeze to death. Fortunately such frigid cold snaps don't occur every year.
Other avian sleeping arrangements are a bit more unusual. Bobwhite sleep in a tight circle on the ground, all heads facing outward. The body contact helps them to conserve precious body heat, and the outward orientation allows wary eyes to detect danger in all directions. And when there's a lot of snow cover, ruffed grouse bury themselves in snowdrifts, where the snow itself insulates the grouse from plummeting outside air temperatures.
First Published November 11, 2012 12:00 am