Birds utilize a number of behavioral adaptations that afford them some protection from frigid air such as we have been experiencing lately. They include sunning (turning their backs to the sun, exposing the largest surface of their bodies to the heat), shivering, tucking (placing one foot up inside feathers while standing on other leg, or squatting to cover both legs and feet with feathers; tucking their bill into their shoulder feathers and breathing air warmed by their body), roosting together in small groups (often in a small cavity, so as to conserve heat) and, most obvious of all, fluffing themselves up (creating air pockets that are warmed by body heat).
While feathers serve many purposes, from helping to attract a mate to providing camouflage, one of the most important jobs they have in winter is to keep a bird warm and dry. A bird’s body heat (the average bird’s body temperature is 105 degrees Fahrenheit), warms the air between its feathers. Birds fluff up in the cold to trap as much air in their feathers as possible, as the more trapped air, the warmer the bird. They can appear two or three times larger than they appear on a 32 degree day. This insulation is effective because it also is a barrier to water. The oil that birds apply to their feathers when they preen serves to waterproof the feathers. (Photo: Dark-eyed Junco)