They can find sufficient quantities of their preferred food or simply change their diet by finding high-energy substitutes in dormant insects, seeds, carrion, suet and backyard bird feeders. Birds have evolved several properties for surviving in cold weather. One of the most common and least expensive, in terms of energy use, involves the birds' feathers. As temperatures go down, birds fluff up their feathers by working tiny muscles located in their skin. The fluffing action traps and holds the air surrounding the skin.
Birds can also grow a more dense cover of feathers.
Tiny birds such as chickadees have more feathers relative to their size than the larger birds. Most warm-blooded animals will huddle as a natural defense against cold. The smaller the animal, the more beneficial this strategy can be. Many birds keep warm by huddling together in trees or any place where there is protection from storms or chilling winds. Some birds, such a ptarmigan, grouse and common redpolls, use the insulative properties of snow to protect them from cold air.