Summit Outside: How birds that do not migrate survive the winter
Special to the Daily
In my last article I wrote about bird migration. What about the birds that live year round in Summit County? We see quite a variety of birds here in the winter including, crows, ravens, chickadees and nuthatches.
Since a major reason for certain species to migrate is a source of food, it would stand to reason that they would have to find a food source or hibernate. We do not think of birds as hibernators, but they must have adapted a means of staying warm on those bitter winter days when a few minutes of exposure on our skins would mean frostbite. Do you wonder where the birds are on those bitter winter nights when the wind is howling and all we want to do is huddle by a nice fireplace?
Why don’t those skinny, little, toothpick legs freeze? Birds actually use several tricks to keep their legs from freezing. For instance, they can stand on one leg and pull the other up under their feathers when one leg starts getting too cold. If it gets really cold, they can squat on their perches and cover both legs. If you see a bird doing this, he or she very well may be getting uncomfortably cold legs.
Birds also have unique scales that cover their feet and legs, which minimize heat loss.
The circulatory system in their legs allows them cope with cold temperatures as well. Warm arterial blood on its way to the bird’s feet passes through a network of small passages that travel along the cold returning venous blood from the feet. The circulatory vessels act like a radiator exchanging the heat from the out-going arterial blood to the cold venous blood. This system insures that no heat is lost and the bird’s feet receive a constant supply of warm blood. The good blood supply is a reason why ducks can swim in freezing water and not freeze their feet and legs.
Birds have a higher body temperature than humans, and a higher metabolism. While the average human’s body temperature is 98.6º F, the average bird’s body temperature is approximately 105º F.
Birds have feathers coated in oil which is important for waterproofing, and snow proofing as well. Some birds actually grow more feathers during late fall to give them extra protection for winter, much like mammals that winter over and grow a thicker fur coat. They can also fluff up their feathers during particularly colder days and nights, which can reduce the amount of heat loss by up to 30 percent.
Bird body feathers are like little down jackets that hold the heat of the body.
Other methods to stay warm include tucking their bills into their shoulders, fluffing out their feathers to create air pockets for additional insulation.
Birds have a special kind of white fat which differs from the “fat” in humans. It is used as a high-energy fuel to power the birds warming process, which is shivering. When they shiver they produce five times more heat than normal and can maintain a normal body temperature for six to eight hours at very cold temperatures. They will often try to store extra fat for winter.
Crows can go into a state called torpor. They lie on the ground with their bills half-open when sunning themselves. This is actually a state of unconsciousness where their core temperature drops approximately 10-12 degrees. This causes the breathing and heart rate to drop and the bird’s body then needs less energy to maintain body temperature.
On sunny winter days, many birds will take advantage of solar heat by turning their backs to the sun, thus exposing the largest surface of their bodies to the heat and raising their feathers. This allows the sun to heat the skin and feathers more efficiently. Their wings and tail feathers may also spread while sunning.
Many birds roost in large flocks at night and crowd together in a small, tight space so they can share body heat. You can often see thousands of crows roosting together. As many as ten bluebirds have been found to roost in the same tree cavity on cold nights. Groups of chickadees may be found huddled together in logs and cavities. Birds can also use dense shrubs and tree cavities for protection against the cold.
Birds that don’t migrate must rely on food sources such as berries, seeds, and grains. They can supplement their natural diets with the food they can get at bird feeders. Many birds also cache food in various locations such as bark crevices, knotholes and pine needle clusters in the fall.
Research shows that some birds such as chickadees develop new brain cells to help them remember and recover their cached food.
In general larger birds cope with the cold better than smaller birds. Small birds need relatively more food than larger ones, and they generally eat smaller items, so they are more likely to be affected by a blizzard. A small bird’s survival may depend on how well it can conserve energy during a storm.
A chickadee, for instance, will increase its feeding intensity during cold weather.
Put out winter bird foods such as suet, seeds and other bird foods high in fat. Put out fresh water daily. This will save them the energy of trying to find water. Keep your feeders full, and check daily, and you will be rewarded by getting a close look at these wonderful, feathered friends.
Breckenridge resident Dr. Joanne Stolen is retired from teaching microbiology at Rutgers University.
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