![]() ![]() Instead, explains Swanson, they are experts in shivering. These small creatures can't put on too much bulk for aerodynamic reasons. When asked which birds are toughest winter survivors, Swanson points to little ones like chickadees. As a result, some birds spend the vast majority of their daylight hours seeking fatty food sources, making feeder food even more precious for surviving a frosty night. "They put on insulation." Their insulation often involves growing an extra set of insulating downy feathers.īirds can also put on fat as both an insulator and energy source: More than 10 percent of winter body weight may be fat in certain species, including chickadees and finches. "Big birds, like geese and grouse, do what we do," says physiologist David Swanson at the University of South Dakota. Cardinals, impossible to miss against the snow, and other smaller birds puff up into the shape of a little round beach ball to minimize heat loss. They also huddle, bunching together to share warmth, and try to minimize their total surface area by tucking in their head and feet and sticking up their feathers. Sparrows, for example, seek out shelter in dense foliage or cavities to avoid the elements. ![]() To make enough heat, and maintain it, they've evolved many different strategies-some similar to our own. Like us, birds are warm blooded, which means their bodies maintain a constant temperature, often around 106 degrees Fahrenheit. But in exchange they have to endure the cold. These winter birds have a better chance of maintaining their territory year-round, and they avoid the hazards of migration.
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