Black-capped chickadees adapt to winter
Black-capped chickadees adapt to winter
Quite a few times the subject of avoiding winter’s cold has come up between my friends and me. My friends understand why animals migrate and hibernate. They also understand the idea of “over wintering” and finding shelter from the weather until it improves. Chickadees at the feeders during the worst days of winter are a little harder to understand.
The Black-capped chickadee (Poecile atricapilla) is a small, handsome bird.
They are about 4 to 5 inches long with a wing span of 8 inches. The black markings on the forehead, crown and neck (bib) and white cheeks makes them easily recognizable at the feeders. The rest of the body is off-white with darker grays on the wings and tail. The black bibs of the males are larger than those of the females and the bills, legs and feet of both sexes are usually grayish-black.
Chickadees are found in forests of the northeastern and north-central United States up through southern Canada. They migrate; spending most of the winter in the more southern regions and most of the summer in the northern.
Habitat is chosen by food supply, nesting sites and by the need of this very small bird to avoid the wind. The forests of Pennsylvania are well-sheltered from wind, are an ideal habitat for these remarkable birds.
Chickadees eat berries, seeds, insect eggs and larvae, gypsy moth and tent moth caterpillars, mites, spiders, snails and even, in the winter, fat from carrion.
How does a bird so small survive the bitter cold of winter? The answers are more complicated than one might think. Chickadees are smart about finding and storing food, and their bodies have adapted so they can endure the cold days of winter. I am exhausted just thinking about what these small birds are up against.
We pride ourselves on geocaching but our skills are nothing compared chickadees’ caching skills. And, obviously, they don’t use technology to help them out. One researcher found that chickadees could locate a cache of high-energy food 28 days after the birds had hidden it. Another researcher found that chickadees will remember which caches have the highest-energy foods and consistently raid those caches first.
In the fall they begin to cache food by storing it in bark crevices, pine needle clusters and knotholes. These caches are relied on heavily if other food sources disappear. The interesting thing researchers have discovered through recovered specimens is this: the chickadees’ brains are larger in the winter than in other seasons.
Relying on memory means the birds have to accurately relocate cache sites, recall which caches they have previously emptied, recall which sites they have discovered empty and recall what type of food is stored at a cache site. It is estimated that chickadees cache as many as 100,000 food items per year across a territory of between 3 to 12 acres and they do not reuse cache sites. This is simply amazing to me because there are days I cannot recall where my keys are.
Something called spatial memory is used to relocate caches as well. Just as we use landmarks, so do they. Rivers, mountains, valleys and other landforms help them to navigate back to their caches. Some research has shown they use typical objects found in our yards and parks as reminders to help them as well.
Chickadees can lower their body temperatures at night and enter a state of hypothermia. Their normal body temperature runs at about 108 degrees. On cold nights they can drop their body temperatures to 85 degrees. The ability to do this reduces the rate of fat consumption by about 25 percent. We would find it difficult to survive at that low a body temperature, even though our normal body temperature is 10 degrees cooler than that of the chickadees. What amazes me is that chickadees can fly to avoid predators when they’re in this hypothermic state.
Chickadees replace their feathers at the end of the summer. When researchers looked at the difference in weight between summer plumage and fall plumage for a number of bird species, they found the new plumage weighed about 25 percent more than the old.
Chickadees also have remarkable control over their feathers and can fluff them to increase insulation. Plus, their feathers are extremely dense compared to birds of similar size.
And, here I thought I was pretty clever donning that down-filled coat!
Carbon County Environmental Education Center is located at 151 E. White Bear Drive, Summit Hill. Call 570-645-8597 or visit https://www.carboneec.org.