When you get out of bed on a cold winter morning, you step into a heated room. You get dressed in warm clothes, eat a good breakfast and head out the door to walk to the bus stop. Wait a minute -- you forgot your hat and gloves!
We human beings have invented effective ways to cope with the cold temperatures winter brings. We provide ourselves with cozy shelter and clothing, and we can get food easily. All it takes is a trip to the grocery store. But have you ever wondered how animals cope with the hardships of winter?
There are three basic tactics animals use to survive in the cold. Some leave cold areas, traveling to warm wintering grounds in the south. This survival strategy is called migration. Some animals spend the warm months storing up lots of body fat. As the days shorten and the air gets cooler, these creatures find protected caves or dens where they sleep away the winter months. This technique is called hibernation. Then there is a third method, called resistance, used by the winter-active animals that stay put and tough it out.
Only a few mammals actually hibernate throughout the winter. The woodchuck is one of them. As it sleeps, the animal's life processes slow way down. They practically disappear. The woodchuck's heart rate drops from about 80 beats per minute to about four, and instead of taking 25 breaths per minute, it takes one breath every five minutes or so. Its body temperature drops to near freezing. These changes mean that the animal's body uses as little energy as it possibly can. It can make it through the winter on its supply of body fat.
Most people think of bears as hibernators. While it's true that they do sleep through much of the winter, they sleep lightly compared to true hibernators like the woodchuck. And they wake up from time to time. On a warm day, they may even emerge from their dens and take a stroll. Female bears give birth to cubs during the winter months. The black bear, for example, has a cub (or two) in January or February. The mother bear licks the cub clean, attaches it to a nipple so it can eat and goes back to sleep. As she sleeps, the baby feeds, and feeds and feeds. By the time spring calls the bear and its cub out into the world, the mother has gotten slim. But the baby is a butterball.
Winter-active birds and mammals have to keep themselves warm to survive. They grow more feathers or thicker fur coats. Even your pet cat and dog do this. Warmth also comes from burning the energy locked up in food and body fat -- so the animal has to eat, too. This is hard in wintertime, when the ground is often covered with snow. Some animals solve this problem by storing up food during the warm months and then eating it in winter. You have probably seen squirrels collecting nuts in the fall.
Another good trick animals use for staying warm is huddling. When a few small creatures curl up together, less body surface area is exposed to the cold. Congregating, or gathering, in dens is also a good way to keep warm. Small rodents called voles gather in dens underground. A group of five to 10 crowd in together. Their body heat warms up the den -- raising its temperature as much as 25 degrees higher than the air outside. When one or two of the voles go out to search for food, the others stay behind to keep the nest warm. That way, the voles returning with food come back to a nice, warm, centrally heated house.
But what about birds? They can't add much body weight, because then they'd be too fat to fly. They don't live in dens, and their bodies aren't designed for comfortable huddling. Even so, birds manage to get through the cold season pretty well. You see them all over this area -- especially if you have a bird feeder near your house. On a cold day, they fluff out their feathers to provide extra insulation. They pull their necks in close to their shoulders to reduce the amount of the body exposed to the air. They shiver to produce heat. And they eat as much as they can find. They have to. During one long, cold winter night, a bird may burn up more than one gram of its body weight. If a human being burned energy that fast, a 150-pound adult would lose 20 pounds every night.
When you walk home to your warm house this afternoon, keep your eyes open. You may see some winter-active animals going about the important business of survival. Try This
While birds are experts at finding food, they can use a little help. If you put a feeder out, you'll be doing the birds a favor. Put it near trees or bushes where the birds can retreat for shelter if danger -- like a cat -- sneaks up on them. But remember: Once you begin, you must keep the feeder filled until late spring when wild seeds are plentiful again. The birds will come to depend on your food.
Feeding birds in winter doesn't have to be complicated or expensive. It's nice to have a fancy feeder hanging from a tree, but birds will also happily eat sunflower seeds spread across the top of a picnic table or bird seed piled on top of an old stump. Put a plastic tray under the seeds. Be prepared to clean up the mess of shells when spring comes, though, or you'll be popular with the birds but not with your parents.
Catherine O'Neill is a free-lance children's writer based in Silver Spring.