The weather is harsh today. Snow covers the ground. Wind is expected around 30mph from the northwest, driving temps below zero where they’ll stay for several days. The trees in the woods to the north and west of the house moan and creak as they sway bare branches in the wind.
The wind chimes on the porch sing a pleasant melody. I shiver just thinking about going out there!
But what is that? The song of a black-capped chickadee (Poecile atricapillus) swinging on his squeaky gate. He has not migrated south for the winter. How will this little fellow survive where I would freeze to death?
It turns out that the little fellow has several strategies. He has to stay warm, and he has to eat a lot. The most obvious thing he does to stay warm is to fluff out his feathers. He looks twice as fat as he did last summer, but in truth it’s not fat—it’s feathers.
Feathers are one of nature’s best insulators. Our little chickadee has two general kinds of feathers—contour feathers and down feathers. We all know that down feathers are warm, whether they’re in a jacket or a feather bed. The chickadee grows these fluffy down feathers next to his skin. Each feather has a hollow central shaft, with little barbs branching off on either side. These barbs in turn have their own little branches. On the outside contour feathers, like say the wing feathers, these little branches have little hooks on them that join them to their neighbors to form a smooth outer coat. The down feathers don’t have the hooks so instead of forming a nice smooth coat, they create a fluffy inner lining. The fluff of the down feathers traps tiny pockets of air heated by the bird’s body heat, so our little chickadee is in effect wearing a nice warm light-weight down jacket covered by his outer feathers. When he fluffs up his feathers, he makes mor space for warm air, effectively thickening his down coat for more insulation and warmth.
But his feet and legs are bare. Why don’t they freeze? The answer lies in carefully regulated cold feet and a heat exchanger. His feet remain at just above freezing. He doesn’t seem to mind that they’re cold. Of course, they have blood flowing to them from the 105-degree body core. To keep those little toes from wasting all that hard-won body heat, the descending arteries in his legs lie next to the ascending veins, transferring most of the warmth from the blood in the artery to the blood in the vein. His feet stay cold. The tendons continue to function at this temperature, allowing him to sit or hop along on a branch without falling off.
This little fellow, who weighs less than half an ounce, maintains a core body heat of about 105 degrees. That, plus his jacket, keep him warm throughout the day while he ceaselessly hunts for food. He has to eat his body weight every day to keep that little furnace going. He’ll eat seeds, insects, caterpillars–whatever he can find. Throughout the day, he sticks with a group of friends who share their food finds with each other. At night, he hopes to find a hollow of some sort to protect him while he lowers his body temperature several degrees and sleeps, often shivering all night to keep warm. That uses up all the calories he found yesterday, so he starts over again in the morning.
The black-capped chickadee is native to North America and was first described in 1760. Both males and females wear a black bib and a black cap that comes down past their eyes. Between the cap and the bib are white cheeks and a short dark beak. The back and tail are gray, with lighter underside and accents of rust on their sides. Their wings are rounded, with gray feathers edged in white. Chickadees are smaller than sparrows, with a body length of about 5 inches and a wing span of about 6 inches. For all that, they weigh about a third to a half an ounce.
During the winter, the chickadees and other small songbirds flock together in what is known as a “banditry” of chickadees. They work together to find and share food, increasing everyone’s chances of survival. A chickadee will also stash food if it’s had enough for the day, and remembers where and what it stashed for future consumption. They love bird feeders and can be very bold around humans. The banditry or flock also allows them to watch for and warn each other about predators like hawks and owls and to find safety in numbers.
Since we put up a bird feeder this fall, we’ve seen this banditry of chickadees every day stoking their little furnaces with birdseed from the feeder.
Photo by author