Do birds get cold? Here's how they stay warm in freezing winter temperatures.

When you step outside into the cold winter air, you may start shivering. Our bodies do this to keep us warm – our muscles tighten and loosen quickly, creating enough energy to give off heat.

Humans rely on thermoregulation to keep warm in the wintertime. We bundle up with cozy hats and jackets. We wear gloves and warm boots to keep our extremities cold. We turn on the heat in our homes.

But a bird's home is the great outdoors, so how do birds keep warm in the year’s coldest weather? Here’s everything you need to know about how birds survive in frigid temperatures.

How do birds keep warm in the winter?

Birds are warm-blooded just like humans, meaning they have a fairly consistent internal temperature and use regulatory mechanisms to maintain it in cold environments. Birds have a consistent internal temperature of about 104 degrees.

Birds keep warm by shivering, fluffing their feathers, cuddling together and tucking in their feet and bills.

Birds increase their body weight in late summer and fall to prepare for winter. They also trap pockets of air around their bodies using their feathers, the U.S. Fish and Wildlife Service reports. Some birds use the oil produced from the glands near their tails as weatherproofing, while other species grow feathers with tips that break down into a powder used for the same protection.

Waterfowl like gulls, ducks and geese often stand on ice or cold ground, so they use a countercurrent heat exchange system to keep their feet warm. The cool blood from the foot travels through the arteries while heat transfers from the warm arteries to the cold veins. Their feet have little muscle or nerve tissue, so they can withstand low temperatures longer than humans can.

Birds of a feather ... huddle together? Birds do this to stay warm, crowding together in trees or shrubs to share body heat and conserve energy.

Why do birds fly south in the winter?

Northern Hemisphere birds migrate with food availability; they move south in winter when insects and plants are harder to come by. There are permanent resident birds who do not migrate, short-distance migrants who may move to lower elevations, medium-distance migrants who travel a few hundred miles and long-distance birds who typically move from North to Central and South America.

According to Cornell Lab’s All About Birds, migration is likely triggered by changes in day length, temperature, food supply and genetics – even some housepet birds have “migratory restlessness” in the spring and fall.

What do birds eat in the winter?

Residential birds that spend the winter in the north don't have as many options for berries as in the summer months, so they typically stick to seeds and whatever insects they can find.

If you have a bird feeder, the Humane Society recommends putting out black-oil sunflower seeds, white proso millet and peanuts for high protein and fat content in the winter months.

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This article originally appeared on USA TODAY: How do birds stay warm in winter? They use these four tactics.