When the wind is howling and the temperature is dropping, it can be hard to imagine how your backyard birds are making it through a frigid winter night. Fortunately, bird anatomy and instinct combine to give them the edge they need to survive even the coldest winter nights.
For example, their feathers serve as insulators. They also maintain a warm core body temperature, even when they are at rest. On cold nights, some species, such as waterfowl, minimize heat loss by a process called countercurrent heat exchange. In other words, chilled venous blood that is returning upward to their legs from the feet passes through an intricate network of blood vessels containing warmer arterial blood and is reheated before it reaches the extremities.
They also use their bodies to generate heat by shivering. As the shivers occur, their metabolic rate goes up, and they create more body heat to keep them warm.
In addition, they may huddle together in groups to create a more efficient source of warmth. This behavior is especially important for small birds like finches, chickadees, nuthatches, wrens and bluebirds that have limited capacity to store energy.
Another roosting option that some bird species favor is grapevines, which provide thermal cover and a natural insulator for birds during the night. For these species, a vineyard offers additional benefits such as a rich food source and safety from predators.