Decemeber 14, 2007
By Susan Benson
Director of Education
Cable Natural History Museum
You may have noticed that the cold weather tends to dampen our cars’ fuel efficiency, meaning we have to burn more gas in winter than in summer to travel the same distance.
The same holds true for birds that spend winter in the cold north. Birds, like cars, run high-powered engines at hot temperatures—somewhere between 102 and 112 degrees Fahrenheit for most birds. They need a lot of energy to keep those engines burning, and this at a time when food is least available! How do they survive?
Their first goal is energy conservation, and birds go about this in a number of ways.
Birds have multiple layers of feathers that help them withstand the cold and maintain body temperature. When birds fluff up their feathers in the winter weather, they effectively double their feather volume, and this thick plumage traps an insulating layer of warm air next to their bodies. It would be as if your clothes magically changed into a puffy quilt when it got cold.
Feathers, however, do not protect a bird’s bill, legs and feet. Birds’ beaks are made of a hard material similar to their toenails that is not very vulnerable to harm from the cold. Exposed legs and feet, though, can suffer cold damage. This is where a clever adaptation allows many birds to survive the winter months, even when their legs and feet are in the icy water.
Here’s how it works: the large blood vessel carrying warm blood from the bird’s body into its leg separates into many smaller vessels. The vein carrying cooled blood back from the foot into the leg also divides into many smaller veins, which run alongside and between the blood vessels.
The birds move the heat from the warmer blood vessels to the cooler blood in the veins before the blood reaches the bird’s body—a strategy called “counter current heat exchange.” Birds also can condense the amount of blood entering the legs and feet by reducing the size of the arteries. These adaptations can decrease heat loss in legs and feet by as much as 90 percent.
Another trick birds practice is standing on one leg and lifting the other up into their breast feathers to keep it warm. Often you’ll see ducks in winter weather perched on the ground; when they do this, they wrap up their legs and feet in protective, warm feathers.
Additionally, many bird species that winter in the north can lower their heart rate, respiration, and metabolic rates to conserve heat and energy. Chickadees, for instance, drop their body temperatures from 10 to 20 degrees on very cold nights. Other birds wintering south of here, like some doves, swallows, hummingbirds, titmice, swifts, and nightjars, also can enter this state of dormancy, or torpor, to survive an unusually cold winter night.
During the cold winter nights, birds like woodpeckers and other species curl up inside tree cavities for cover and heat. Other birds crowd together in whatever nooks or crannies they find. Some species of birds that inhabit open fields in the winter months will burrow into snow holes to escape the winds and chill.
Of course, even with all these strategies of energy conservation in play, birds need to eat in order to replenish their energy. Fuel efficiency can only take you as far as you have fuel.
Some birds change their menus in winter. A nuthatch, for example, usually eats insects in summer, but changes its main dinner menu to seeds and nuts in the winter.
In a harsh winter, where snow and ice covers sources of seeds and insect larvae are hard to get to, many bids do die of starvation. This, of course, is why winter bird feeders can be so important in our region. If you have a chance, stop by the Cable Natural History Museum and see our exhibit “Birds in Focus.” It features a display of bird feeders, advice on feeding tactics, and many other resources that can help you learn about safely feeding birds through the winter.
Nature Watch is brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 43570 Kavanaugh Street or on the web at www.cablemuseum.org to learn more about exhibits and programs.