Like some of us, many birds flee the cold, northern regions to winter somewhere warmer – true “snow” birds. But this requires migrating enormous distances twice each year. All this effort to avoid howling snowstorms and below freezing temperatures.
However, like some of us, some birds stay. And they face the dreadful winter head-on against seemingly insurmountable odds.
So, to beat those odds and to survive winter, birds need to solve two problems: staying warm enough and finding enough food.
How do they keep warm? Some are simple concepts. Some require a bio-medical degree to understand.
Pack on some extra body weight. In anticipation of the long, cold winter, birds pack on extra body weight or fat during the late summer and fall – same as us?
Shiver. We humans shiver when we are cold. This is a means to generate metabolic heat. So do birds. Birds shiver by creating muscle contractions.
Put on a “Winter Coat”. Birds do put on a “winter” coat. Down feathers cover the majority of a bird’s body underneath the longer, exterior feathers. Birds can puff these up - a process known as piloerection. This fluffy barrier traps pockets of air close to the body which are then heated by the radiated warmth from within the bird. Piloerection can retain nearly 90% of their core heat. In cold weather foraging on the ground, Dark-eyed Juncos, American Tree Sparrows, and House Finches will drop down and cover their legs and feet with their breast feathers or "winter" coat, while pausing in their search for food.
Perch and Sun. In addition, many small- and medium-sized species of birds will assume sunning postures in which they squat or sit with their feathers slightly erected, and wings drooped. Usually, the bird is oriented, so the back is fully exposed to the sun's direct rays. Red-tailed Hawks may just bask into the morning sun while perched high in the trees.
Huddling. Smaller birds, like House Sparrows and Black-eyed Chickadees, American Tree Sparrows and other winter birds, conserve their heat is by huddling together. They form a line or a circle with one another, and throughout the night they will rotate position as the ones on the outermost edges lose more heat than the ones in the middle of the line.
Burrow into snow tunnels. Common Redpolls have a remarkable ability to survive cold temperatures, roosting in tunnels under the snow during winters. These tunnels may be more than a foot long and four (4) or more inches under the insulating snow
Internal HVAC zones. Black-capped Chickadees endure the winter in their bare uninsulated legs and feet. These birds use a countercurrent heat exchange system where cool blood coming back from the foot travels through veins grouped around arteries that are sending warm blood from the body to the foot and heat is transferred from the warm arteries to the cool veins. This countercurrent heat exchange system keeps the core body temperature high – around 104 degrees. Yet their feet and toes remain flexible and functional even as they cool down close to 30°F. Periodic increases in blood flow allow a little more heat to reach the foot and prevent it from freezing.
Regulated hypothermia. - Some birds save energy by allowing their internal thermostat to drop. Some birds like hummingbirds undergo torpor nightly as their body temperature drops close to outside temperatures. But torpor is not too common in winter birds, because the morning warm up would take too much extra energy. Instead, winter birds undergo a more moderate version called regulated hypothermia, reducing their body temperature as much as 20 degrees.
So, the first part of the survival equation is solved by those mechanisms, but how is the second part?
Surviving winter under these conditions can be helped enormously by us, simply by filling our feeders during the freezing weather. And if you do this, you will also get the benefit of some excellent winter-time birdwatching from our own home.
For more information on the Winter Bird Behavior and sources of information used in this blog (these are the sources that I am using to learn as I blog), please visit All About Birds, Audubon Society, U.S. Fish and Wildlife Service, Washington Post (Gina Rich) article, and Stanford Birds essay (Ehrlich, Dobkin, and Wheye). And the Cornell Lab of Ornithology provides a wonderful source of information for anyone interested in learning more about birds.
The Carillon at Stonegate community is very fortunate to have a variety of wetland, forest, and prairie environments conducive to a variety of birds and other wildlife. Our community and the Kane County Forest Preserve does an exceptional job in maintaining this natural environment – both for the benefit of the birds and wildlife and for our residents to enjoy.
Take a hike and see what you can find – and identify!
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