January 23, 2012

Flying Into Winter

By Margaret Gillespie

A thick hemlock tree thrives just outside my office window and I am pleasantly surprised when birds unexpectedly appear on its branches to open sunflower seeds from the nearby winter feeding station. At a time of year when tracks in the snow are the major evidence of local wildlife, these lively visitors are a welcome burst of color and action. During this frosty, snowy, windy season, it is amazing how birds survive without all the technology that we humans depend upon for warmth and food. We might be tempted to call their existence the “simple life” but birds’ winter adaptations are far from simple!

Black-capped Chickadees are frequent and entertaining visitors to bird feeders. Have you ever noticed that they come in a flock and seem to be on a schedule? This winter grouping generally includes about six birds consisting of a dominant pair that nested during the summer, some of their offspring, as well as other juveniles and adults. Specific bird feeding stations become preferred sites on their daily circuit of three or more good foraging spots. Chickadees may be the ultimate “weight-watchers,” except that they need to gain about 10 per cent of their weight in fat per day in order to stay warm over cold winter nights. Don’t even think about how you could compete by adding 12 or 15 pounds of fat to your frame from sunrise to sunset! At night these birds turn into the ultimate energy conservationists by lowering their body temperature. Peter Marchand in Life in the Cold describes how chickadees become hypothermic by reducing shivering to the point where their temperature lowers 10 to 12 degrees Celsius, with the result that they use 20 per cent less energy in heat production.

A key component of winter survival for birds is their insulating feathers. In late summer, many birds begin molting or losing their summer breeding plumage and replacing those feathers with new ones. Although often more drab, the new plumage in winter resident birds has been found to weigh 25 per cent more than the old plumage, providing needed insulation. Smaller birds have more surface area for their size from which to lose heat but birds like Chickadees and Kinglets actually have proportionally more feathers than much larger birds. In addition, as birds fluff out their feathers, air is trapped and warmed near the body. Birds preen to take care of their feathers and to spread oil from a gland near the base of their tail, preventing rain and wet snow from getting through to their insulating down.

Where is a good sheltered spot for the night? Chickadees retire to thick evergreens which protect them from wind. A tiny tree hole makes a good spot for one chickadee although the bird emerges the next morning with a temporarily curved tail! But what about those exposed legs and feet? Winter birds have a special trick under their scales -- it’s a wild version of a heat exchanger! In the legs and feet, arteries bringing warm blood from the heart are right next to veins bringing cold blood back from the feet. Arterial blood is cooled somewhat so not so much heat will be lost to the air through the feet. Venous blood is heated somewhat so cold blood will not be returning to chill the bird’s core. Of course there is always the one-legged bird trick where one foot is drawn up into the feathers. Perhaps the most secretive ploy is one the habit ruffed grouse have of tunneling into the snow to spend the night under an extra insulating blanket – a good spot during snowstorms too.

With all these winter adaptations tucked under their feathers, do birds really need our help? Hibernating insects, winter berries and seeds can be challenging to find. As we all know, winter can be unpredictable. While providing a bird feeding station is not essential, it may give birds, especially first year birds, that extra boost needed to get them through our harshest season. Besides, bird feeding is an opportunity for us to observe birds and their behaviors – a fascinating pastime. Watch the parade of Nuthatches, Goldfinches, Tufted Titmice and Cardinals, to name a few. Put out black, not striped, sunflowers that give birds lots of food energy. Don’t forget to hang some suet or peanut butter to keep the Woodpeckers coming. Birds will place your feeder on their internal daily map so try to be consistent with your feeding and be sure food is out early in the morning when they need to replenish their energy, even if it means loading feeders in the evening.

Winter isn’t just for the birds! Check out the winter landscape on foot, snowshoes or skis. Take some of the lessons you learn from birds with you – insulate, eat well and be active!

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