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In my younger days, I loved to go grouse hunting, especially during the winter season. Grouse hunting without a dog is certainly one of the most strenuous hunts.
The weather made these winter grouse hunts even tougher. The temperature was usually in the single digits and felt like zero when the wind was blowing. During these hunts, I always trudged through heavy cover, with many evergreen trees that were used by the birds to block the wind. I remember seeing a flock of robins on one of these hunts. This sighting was unusual here in Bradford County because most robins head for the sunny south in early fall.
There are many folks that dread winter, with its snow and ice, and travel south to avoid the icy fingers of winter. And then there are others (Mary Alice) that love winter and enjoy walking through the snow.
Birds also face winter in similar ways.
We have about 340 species of birds that leave North America to winter in tropical regions; however, many birds remain in our area year-round.
Birds have a greater resistance to cold than mammals. Heat loss from a bird's body is not only diminished by a coat of feathers, which encircles and insulates with confined air.
Also, a bird's legs and feet are tendinous, with no fleshy parts as in mammals. The bill is made of horn and gives up little heat.
There is very little skin exposed to the air, no fleshy ears, tail or legs from which heat is lost. When perching, a bird can tuck one foot into its belly feathers, and on a very cold day, a bird can also tuck its bill into feathers. A bird also has air sacs under its skin that can give protection with an insulating air against the cold.
Resting birds will shiver for a short-term adjustment to the cold, which increases its heat production by converting muscular energy into heat; however, this used energy must soon be replaced.
There are birds, such as the evening grosbeaks and northern finches, that can store relatively large amounts of food in their crops, which helps in maintaining a high metabolism for overnight. The common redpolls are able to survive colder temperatures than other songbirds. Research has shown that a redpoll has a higher rate of energy intake due to a special storage pouch in its esophagus, which the bird fills with food just before darkness.
A redpoll also selects high-calorie foods, such as birch seeds over other foods. During the night this food is digested, allowing the redpoll to maintain a high metabolism.
In early fall, we could still have birds in our area if a cold spell hits. At this time, birds, such as hummingbirds, become torpid overnight, lowering body temperatures and metabolism. By doing so, they conserve their food energy supply. Mourning doves can also be found in our area during the cold and snowy winter months when food becomes scarce.
The mourning doves do not become torpid but can use a physiological mechanism that decreases their metabolic amounts and conserves energy, which is an aid to survival.
Have you ever wondered why some birds remain in the area throughout the winter months, while others migrate to warmer climates? Birds that remain in the area year-round can switch from an insect diet to a diet of seeds.
During the extreme cold and snow of winter, smaller birds appear to save body heat by roosting in sheltered places and reducing their activities. Chickadees, nuthatches, and woodpeckers sleep in holes in trees; up to a dozen bluebirds have been known to pack together inside a nesting box; grosbeaks and cardinals roost among the densely needled branches of coniferous trees.
On a bitter cold day, with heavy snow cover, I was grouse hunting when I came upon a wisp of steam coming from a small hole in a snowbank. I leaned over the hole to determine what was causing the steam when a grouse burst out of the snowbank, throwing snow all over and making the familiar wing beat sound.
Although I had read about these snow roosts, I was startled and glad that I did not have heart problems at the time
In Northern United States, a winter's night can be as long as fourteen hours. This means that birds must be able to endure the cold for this length of time without food. Research done on house sparrows showed that these birds could go 67 ½ hours without food during the summer when the temperature was 85 degrees. During winter months when the temperature dropped to 50 degrees, there was a rapid decline in the ability of the sparrows to resist starvation. To survive the winter's cold, small birds must feed every day to replenish energy loss occurring during the night and build up a reserve for the night to come.
Bill Bower is a retired Pennsylvania Game Commission Wildlife Officer. Read his blog and listen to his podcasts on the outdoors at www.onemaningreen.com.