Birds have multiple strategies for keeping warm when the mercury dips. Birds are warm blooded with normal temperature around 106ºF. Some, like sparrows, will huddle together to share the warmth. Others will puff up their feathers and tuck beaks into their down to keep warm. Putting on an insulating layer of fat is another adaptation used by geese, chickadees and finches. Small birds can’t put on too much bulk for aerodynamic reasons. Another technique is shivering. Birds shiver by activating opposing muscle groups which is more effective than an all over trembling.
But what about the body parts not covered with feathers? Amazingly, birds have a countercurrent heat exchange system in their legs and feet. Cool blood coming back from the foot travels through veins grouped around arteries that are sending warm blood from the body to the foot. Heat is transferred from the warm arteries to the cool veins.
And because bird circulation is so fast, blood doesn’t remain in the feet long enough to freeze. Bird feet can also withstand low temperatures without damage because there are mostly tendons and bones with little muscle or nerve tissue. Birds may also alternate standing on one leg at a time or lower their bodies down to cover their feet.
Anhingas absorb solar energy to keep warm. They have an unusually low metabolic rate and unusually high rate of body-heat loss. Lacking the fluffy down insulating layer of cormorants and other birds, they spread their black wings and soak up some rays to get warm.
At night when the temperatures drop, Hummingbirds allow their internal thermostat to lower close to the outside temperature. This is called torpor – during the day they maintain normal body temperature and activity levels, but their metabolic rate and body temperature drop at night to conserve energy. Other small birds like chickadees have a more moderate version of this called regulated hypothermia, lowering their internal temperature as much as 22ºF at night.
It’s amazing how our feathered friends have adapted various strategies to deal with the cold. One way to help birds during winter is having a variety of backyard bird feeders. Chickadees and finches love black oil sunflower seeds. Woodpeckers devour suet feeders. Cardinals and red winged blackbirds prefer sunflower seeds. Fill up your feeders, sit back and enjoy all the backyard visitors you’ll attract.
