Watching the little, darting chickadees at your feeder, have you ever wondered how they survive the freezing winter temperatures?
A chickadee wears its coat year-round, but in the winter, it increases its feather count by as much as 30 per cent. Even with the increase in fluff, a chickadee has a far harder job keeping warm inside its down insulation than you do in your layers of high performance winter clothing.
Chickadees have a high ratio of surface area to heat-generating tissues; in other words, it has proportionally less engine and more cooling surface than human beings. Not only that, a chickadee runs several degrees hotter than a human, its body temperatures averaging about 104 degrees and increasing to 108 degrees on the coldest winter days.
So, how does it manage?
The answer is a unique combination of activity, appetite and a degree of metabolic control that a yogic adept could only dream of attaining.
Chickadees have to work hard to stay warm; during the day they flap and flurry and vibrate, hearts speeding to an astonishing 2,000 beats per minute as their metabolisms race to produce enough heat. The energy going into heat production comes from their food, and during most of the daylight hours the tiny birds tear around in search of things to eat. A bird will eat 20 times as much on a winter day as it does in warmer months, and every scrap of food – every insect egg, every bit of feeder suet or black oil sunflower seed is necessary if the bird is to survive the night.
On occasions when it finds more food that it can eat right away, the chickadee stashes the remains in a handy cache like a squirrel does for later use. Here the high body temperatures which requires so much work to maintain, becomes a bonus. Research indicates that a higher brain temperature may correlate with a better memory. In other words, being hot helps it remember where it left its leftovers. One study found that a chickadee could recall the location of a cache as many as 28 days after stashing it – no mean feat for a creature with a brain approximately the size of a plump pea!
Although a chubby chickadee is a well-insulated chickadee, it’s also slower than its mates. Predators such as owls and hawks watch for these slower birds – as a protective measure, chickadees hang out with their cousins – goldfinches and nuthatches – in large varicoloured flocks, thereby increasing its odds of evading notice by moving about in a gang.
This interspecies communalism ends at sundown. At night, they sleep in a chickadee heap, piled half-ounce on half-ounce inside hollows in trees. Many of these hollows were made by woodpeckers who chisel out several cavities each spring and summer, then find they don’t need them all when fall comes. In their borrowed dens, the chickadees pile together out of the wind in groups of eight or 10.
If a chickadee kept up its hectic metabolic rate all night, it would starve to death before morning. However, once the bird is bunkered in for the long winter’s night, its heart rate slows to a sedate (for a chickadee) 500 beats per minute and its body temperature plummets as much as 20 degrees. The human equivalent of the chickadee’s nighttime torpor would be an ability to drop the heart rate to 15 to 20 beats per minute and the body temperature to just below 80 degrees.
You can see why the ready availability of food is so key to not only the chickadees’, but to all the various birds’, winter survival.
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