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Flight Lines: Resisting the rigors of winter; behaviors meant to survive cold

This extremely dark house sparrow appears to be covered in soot, even on its beak and legs.

Last weekend, I stumbled upon a curious scene. Sitting on the snow under a spruce tree was a blue jay. It looked cold but comfortable. Its feathers were fluffed a little and its head was turned and tucked into its back like birds do when sleeping. I was surprised it let me get so close without flinching; usually jays are pretty wary birds. Only when I reached down and touched it was the truth revealed.

It was dead.

In winter, birds and other organisms are focused largely on only one thing: survival. Lasting until warmer temperatures return is paramount for individuals, as well as populations. Without an adequate daily diet and places to rest (cover, in wildlife management jargon), death is the unwelcome result.

Still, it amazes how many animals continue to thrive under such harsh conditions. But should we really be surprised? After all, they've had thousands of years to practice techniques before zeroing in on ones that work. Those with bad ideas are quickly eliminated from the gene pool; the ones with a better plan survive and pass along valuable inherited traits.

If a person pays attention to winter wildlife, some of these habits are revealed. Take birds, for instance. Roosting locations are not chosen willy-nilly. Rather, birds will most often sit on the southern exposure of trees, maximizing the use of the sun's radiant heat. It also shelters birds from what usually is a cold north wind.

Burrowing is a technique used by such birds as sharp-tailed grouse. Coveys will bury themselves in tunnels beneath the snow, taking advantage of the relative warmth found there.

We also have the cachers. That's right, not only do chipmunks and squirrels hide stores of food, but several bird species do, as well. Blue jays, chickadees, and shrikes are just a few known to store calories for later consumption. The benefits are obvious: less time and precious energy spent searching for sustenance.

One interesting area we don't fully understand is torpidity, which is a sort of waking hibernation. Common poorwills (western cousins of our common nighthawks) have been documented resting with low heart rates, lowered body temperatures, slowed metabolism and breathing rates. To my knowledge, however, none of the species that winter here have exhibited torpidity. But this is an area of study requiring a closer look.

Then there's the group-hug thing. The sharing of body heat through huddling is a behavior of some birds facing cold winter temperatures. Gray partridge, chickadees, and starlings are just a few examples. Once, while walking along the bank of the Sheyenne River just north of West Fargo, I found an eight-inch hole in the snow. When I neared, no less than 12 mourning doves poured out one after another. Obviously, the birds had been huddling for the night.

Others make use of their environment even if it's of a man-made nature. Any number of times this winter, I've stepped out of the house only to scare off house sparrows which had found warmth under the car in my driveway. Perhaps not so surprising is the fact they seem to be concentrated near the oil pan heater.

I received an e-mail recently with an attached photograph of a house sparrow. Mysteriously, though, the bird appears to be extremely dark, almost black. I've had a small number of individual birds in my own yard that exhibited a similar appearance. I don't believe this is some abnormal pigmentation. I think these birds are roosting somewhere where soot is present, such as the exhaust piping from a wood-burning stove.

Finally, there is Fargo's municipal compost area. Some of the piles of grass and leaves are large enough that decomposition is still taking place even in winter. Plumes of steam and snow-free spots are visible during certain conditions. I've seen several different species of birds roosting at these heat sources.

Short of a necropsy, we'll never know why that blue jay perished. Maybe it was just old and its time was up. Or perhaps in some way this individual danced a little too close to that line separating life from death; a line which can become quite thin during winter despite all of nature's survival tools.