When the days of cold rain begin to seem like they have gone on for months, I find myself peering out at the bedraggled balls of fluff at my feeders and wondering how birds survive these winters. The occasional droopy-looking sparrow or siskin reminds me that winters are not easy times for birds.
The first, and most obvious, solution to the coming of winter is the one most birds take: head south for a couple of months! Those that stay behind face two major challenges, staying warm and finding enough food.
As anyone who has worn a down jacket or slept in a down sleeping bag knows, feathers are an incredible insulator. Scientists speculate that feathers, which have evolved from reptilian scales, originated as a defense against cold rather than for flight. Feathers are essentially hollow and serve to hold a pocket of insulating air against the body. Combined with a sleek outer layer of waterproof feathers it is much like wearing a jacket over a down comforter. In warmer weather, the most common danger for birds is overheating under their extremely efficient blankets of feathers!
Feathers only work, however, if the bird is healthy and well-fed enough to keep its feathers cleaned and arranged properly. Sick birds are often conspicuous because their feathers look disheveled.
Food, and unfrozen water, can sometimes be nearly impossible to find in winter. Both are essential for a bird’s survival. Birds are remarkably efficient at using the energy contained in food, especially energy-rich seeds and nuts. Foods can be passed completely through their digestive systems in approximately 15 minutes. What energy is not used immediately is converted to thick fat deposits which fuel the bird through the night.
Smaller birds will eat a third of their body weight in food each day and spend nine-tenths of their waking hours feeding. They are like little wood stoves, crammed full of firewood and blasting out heat all day long.
During periods of adverse weather birds may stay close to dense brush where they can get out of the wind, and at night groups of birds will huddle together to keep each other warm. Bird houses and roost boxes also provide opportunities for shelter.
When at rest, birds prevent heat loss by sitting, holding one leg up against the body or tucking their heads back into their shoulder feathers. These are all tricks for keeping warm, like hugging yourself on a cold day.
If all else fails, birds have the ability to enter a state of torpor, a kind of semi-hibernation in which the body temperature drops very low. Torpor can last from one night to three months, depending upon the species.
Proof that birds are actually very well designed to withstand cold is shown by Emperor Penguins of Antarctica who time their nesting seasons to coincide with the depths of winter, where temperatures regularly reach -80 degrees F. This makes a drizzling northwest day seem tame in comparison, and I breathe a sigh of relief as I watch the bustle of feathered activity at my backyard feeders.