How birds cope with cold in winter

How birds cope with cold in winter
From feathers to fat, birds have multiple strategies for keeping warm when the mercury dips.

Each autumn as many birds begin epic journeys to warmer climates, there are always some species that stay put for the winter. These winter birds have a better chance of maintaining their territory year-round, and they avoid the hazards of migration. But in exchange they have to endure the cold.

Like us, birds are warm blooded, which means their bodies maintain a constant temperature, often around 106 degrees Fahrenheit. To make enough heat, and maintain it, they’ve evolved many different strategies—some similar to our own.

Sparrows, for example, seek out shelter in dense foliage or cavities to avoid the elements. 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. 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.

"Big birds, like geese and grouse, do what we do," says physiologist David Swanson at the University of South Dakota. "They put on insulation." Their insulation often involves growing an extra set of insulating downy feathers.

Birds 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. 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.

When asked which birds are toughest winter survivors, Swanson points to little ones like chickadees. These small creatures can't put on too much bulk for aerodynamic reasons. Instead, explains Swanson, they are experts in shivering. This isn't the familiar tremble that mammals use to generate heat. Birds shiver by activating opposing muscle groups, creating muscle contractions without all of the jiggling typical when humans shiver. This form of shaking is better at retaining the bird's heat.

Another adaptation shared by many species is the ability to keep warm blood circulating near vital organs while allowing extremities to cool down. Take gulls. They can stand on ice with feet at near-freezing temperatures while keeping their body's core nice and toasty.

Read full article:
http://mag.audubon.org/articles/birds/how-birds-cope-cold-winter
Article by Daisy Yuhas
Image credit: Megumi Aita