Winter Birds: Survival of the Fittest
As a naturalist, I know it typically takes ten minutes for wildlife to settle back to business once I am spotted in the forest and perceived as an immediate threat.
Usually, it is a scolding chipmunk alerting other animals to possible danger. On this frigid early winter morning, chipmunks were snug and curled up in their underground burrows, oblivious to my presence. The inquisitive black-capped chickadee, however, did not miss my lumbering figure as I arrived in this wooded area and settled into a camp chair, intent on observing the flock of birds navigate in freezing weather.
Within a few minutes, activity resumed as small songbirds like tufted titmice, nuthatches and woodpeckers foraged for seeds in dangling pinecones and hibernating insects tucked into tree bark. These protein sources are critical for survival on frosty winter days and nights when birds’ fat stores are quickly depleted.
Cooperation between this little flock is also an essential winter survival strategy. Predator alerts (like the one sounded on my arrival), and food discoveries are communicated through vocalizations quickly understood within various species. I am amazed cardinals, for example, understand chickadee “talk” and can react to avoid a hawk by listening to the chickadee’s high-pitched alarm call.
Meanwhile, huddled in my camp chair, with only my face exposed to the frigid air, I felt the chill creeping through the multiple layers of fleece and thermal clothing stuffed under my downy parka. It became difficult to see through the cloud of my exhaled air!
Perched above me on a small overhead branch, a tiny chickadee faced the rising sun, fluffed its feathers as it settled for a brief rest. The bitter cold, which was becoming really uncomfortable, didn’t seem to bother this diminutive bird. Feather fluffing is a heat-conserving posture, an adaptation birds use to survive frigid temperatures and can give them a rotund appearance.
Under these insulating feathers is a layer of fat, stored around the breast and belly area, which acts like emergency fuel storage, essential when snowstorms prevent foraging for food.
Limited daylight and challenging weather conditions propel many small songbirds, like this chickadee I was watching, to cache food. Another brilliant behavioral adaptation, birds will store seeds and nuts in crevices of trees and vegetation for retrieval when food supplies are scant.
If you have bird feeders, watch closely how birds will select a seed, fly off and search for storage spaces. Sunflowers have sprouted under the shingles of my shed roof! Typically, the culprit has been the white-breasted nuthatch, using his pointed bill to insert the seed so securely it never gets retrieved.
I had been hunkering down in this camp chair for about 30 minutes, observing this mixed flock of small birds. The bitter cold was seeping even deeper through my layers, and I started to shiver. We share this ingenious survival adaptation with birds. Shivering muscles generate heat to keep our core temperatures at a set level.
Birds’ fat reserves can be burned through quickly, especially at night when the thermometer plummets. Luckily, our winter birds have a few more survival strategies to deploy. Communal roosting, huddling together during frigid nights, helps conserve precious heat and energy. Sheltered areas like thick evergreen boughs and bird boxes become prime real estate. If you have bird houses, keep an eye out for birds entering them closer to sunset.
Torpor, a deliberate and temporary lowering of metabolic functions to reduce core body temperature, can help birds survive to greet a new sunrise. We put our furnaces into ‘torpor” at night when the thermostat is turned down to save fuel.
At this point in my woods stake out, my feet, snug in wool socks and Baffin boots (engineered for conditions well below zero!) had become painfully numb. How do birds, with their bare legs and feet, not succumb to catastrophic frostbite?!
Another incredible adaptation. In winter, their feet are regulated to approximately 32 degrees. A system of arteries carries warmed blood to the feet, returning the cooled blood through veins adjacent to these warmer arteries. Heat transfers within the legs, recovering the warmth and conserving vital fat stores.
It was clearly time to take my shivering, numb body home, brew some hot coffee, and continue to marvel at nature’s ingenuity.
These little birds, weighing mere ounces, were more adapted for this frigid morning than me, despite my state-of-the-art winter gear. I think I know who won this round of “Survival of the Fittest”!