It’s barely dawn. A tiny bird hops along the branch of a dogwood tree. The frosty morning air doesn’t seem to bother this little chickadee. Other songbirds flit around. Cardinals, blue jays and downy woodpeckers join Carolina chickadees and a host of other songbirds that winter here. Red-tailed hawks and turkey vultures patrol the winter skies.
Many birds, of course, leave the Chesapeake to winter in warmer areas. But birds that can switch from an insect diet to a seed diet can stay put throughout the winter. To survive cold weather, birds have developed some remarkable adaptations.
One of obvious feature that sets birds apart from other animals is their feathers. Birds’ bodies are covered with an outer layer of fairly stiff but flexible contour feathers and an under layer of fluffy down feathers. The contour feathers provide protection against wind, rain and snow. The down feathers act as a layer of insulation.
But even this sometimes isn’t quite enough. Some birds puff themselves up as they wait for their turn at backyard feeders. Puffing is a warming mechanism. Because birds control the position of their feathers through muscular movements, they create and trap larger pockets of warm air near their skin, enhancing insulation.
To minimize heat loss from unfeathered legs, the arteries and veins in the legs of many birds lie in contact with each other to retain heat. Arterial blood from the heart is warm, while venous blood is cool. Heat is conducted from the warm arteries to the cool veins.
Nearly one million waterfowl from northern breeding grounds fly to the Chesapeake region each year. Tundra swans, Canada geese, mallards and a variety of other ducks find that the winters here suit them just fine.
They’re often seen preening. Most birds have an oil gland at the base of their tail. In preening, secreted oil is rubbed with the beak or bill over the feathers, conditions them and creating a shield that blocks wind and repels water.
Waterfowl and waterbirds also have fleshy feet with little blood circulation so they are less sensitive to cold. The inner core temperature of a duck or gull standing on ice may be 104 degrees Fahrenheit but the temperature of their feet may be just above freezing.
All of these adaptations help keep our avian friends around during the chilly winter months. Americans do love their winter birds, spending on average $2 billion dollars feeding a year to feed birds. And why not? Birds add to color and life to an otherwise naked, grey landscape, helping us to chase away those winter blues.
For information on feeding backyard birds see http://library.fws.gov/Bird_Publications/feed.html
Photo by Harvey Doerksen, USFWS