by meg macdonald wildbirdsjax@comcast.net
Winter has finally caught up with us in Jacksonville. Cold blustery nights that totter on the very edge of freezing and days that swing from damp and cold to warm and sunny and back again. In these weeks, as you look out your windows and observe the birds at your feeders consumed in their consumption, has the question emerged - how do they keep warm?
Birds are small creatures, delicate, and situated at the bottom of the food chain to boot. Yet with the odds seemingly stacked against them, we have a plethora of birds. They survive and they flourish. Of course our winter is does not compare with any state north of us; our extremes are only extreme to us. Even so, we may occasionally come across that bird that did not survive the cold; because there will always be weak, sick or old creatures.
But the dozens, hundreds, score that do see spring, how do they keep warm now?
The answer is a wonderful combination of construction, activity, appetite, behavioral adaptations, and metabolic control.
First, construction. Birds are tightly clothed in down feathers. These feathers are great insulators and serve to trap air that is kept warm by the heat produced by the bird. Since Autumn is the time for creatures to acclimatize to lower temperatures, this is the time the feather count increases and may increase up to 30 percent. (I correlate this to my cat’s fur. The thickness of her coat foretells how harsh the winter will be.)
Next, activity. On cold mornings, birds raise their temperatures by fluffing their feathers, slapping, and shivering. With this activity their heart rates can increase to 2,000 beats per minute. This activity consumes energy and thereby increases body heat. Activity can only be maintained through appetite.
On cold days, you can observe birds at your feeders from dawn until night fall. Compared to an average summer day, birds may eat up to 20 times more food on these cold days. Every seed, suet morsel, insect egg, nut and berry makes the difference. Birds will not accumulate fat tissue. So the constant activity and eating is required to maintain their metabolism.
There is a down side to being able to consume such large amounts of food. A chubby bird is a slow bird and a slow bird makes a nice meal for the cold and hungry predator birds such as hawks and owls. But there is safety in numbers. Next, behavioral adaptations. More so than at other times of the year, birds will band together in large groups to increase their individual odds of survival. Plus, at night, birds will flock together and huddle to share body heat. You may also observe activity at your nest boxes at this time. The birds are not nesting. They use these cavities as gathering places to facilitate energy conservation.
Last is metabolic control. If birds had to maintain the same daylight metabolism throughout the night, they would perish. Instead, during the night, their heartbeat slows significantly and their body temperature drops. This ability is the final step in surviving terribly cold nights. Birds can fall into these torpors, a kind of hibernation, and wait out the frigid night.
When daylight comes again, make sure your feeders are full; serve plenty of high protein foodstuffs like suet and peanuts. Have fresh water available for hydration. Then enjoy the frenzy of activity as the birds wake, fluff and begin another day!
Happy birding.
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