Many birds migrate south for the winter but some don’t. So, how do birds survive frigid temperatures? We’ll explore many ways they do this. Some are behavioral, some are physiological.
Birds shiver at varying temperatures. A cardinal shivers at 64 degrees Fahrenheit, while a snow bunting will not shiver until it is -10 C/14 degrees Fahrenheit. The main muscle used in shivering is the pectoralis, or breast muscle. Sometimes leg muscles are also used.
When birds huddle together it reduces heat losses to the individual. One of our local birds, the Pygmy Nuthatch, beds down together in tree cavities. Golden-crowned kinglets huddle closely together on tree branches. Doves will sit on top of each other in rows forming a pyramid. And the masters of staying warm as a unit, the emperor penguin, can withstand drastic sub-zero temps by huddling.
On many cold days, birds appear fatter than they do in summer. This is a bird in a puffed-up state. Birds can retain heat by puffing out and trapping air around its feathers, creating a layer of warmth around itself.
Selecting microclimates by finding sheltered places like dense evergreen foliage, natural cavities, or human made structures is another strategy. Ruffed Grouse and the Common Redpoll will even burrow into the snow to escape cold air temperatures. Woodpeckers will excavate their own winter den in trees.
Temperature regulation is a more complex adaptation to survive the cold. Some birds, like our beloved Black-capped Chickadee, can lower body temperature by reaching a state of hypothermia. It saves energy that would normally be used to maintain a high body temperature. Another strategy birds use is called torpor. Torpor is a hibernation-like state of decreased physiological activity. Birds in this state do not respond to stimulus and are incapable of normal activity. Hummingbirds allow their core temperature to drop by a large amount at night, saving up to 27% of their total daily energy expenditure. Both hypothermia and torpor in birds are accomplished in daily cycles rather than over months-long time periods like mammals.
Access to food and water is a huge contributing factor to whether birds can withstand the cold. If a songbird, like a Bushtit, goes without feeding for a day, it may succumb to the cold. Some larger birds can store more fat on their bodies; but they, too, cannot go a long time without eating in winter.
Even with all these adaptations, some individual birds do not survive the winter. We can help our feathered friends in winter by providing food and water. I love nothing more on a snowy winter’s day than to watch my backyard birds congregate at the feeders. Many birds cache extra food, an interesting behavior. Feeding birds is a way we can give back to the environment for all the damage we have imparted. It helps them and is a fun activity for us. So, enjoy your birds—they are miraculous creatures!
Reference: Gill, Frank B. Ornithology. New York. W.H. Freeman and Company 2007.