Home Is Where the Heat Is
When you're all comfy and warm, watching the snowflakes pile up against the frozen windowpane, you might wonder, what about the poor animals? Stuck outside in the cold. No fire. No cocoa. No blankets. How do they stand it?
Well, it's really people who aren't designed to live in cold climates. Animals have lots of cool ways to survive the winter. Think about it. Geese have built-in down comforters. Bears have fur coats. Robins just fly south. But look at people. No fur. No feathers. No fair! And not everyone can jet off to Florida when it snows.
So what do people have to help them beat the cold? Mainly, our big brains. Still, it's taken us a long time to figure out how to cope with cold weather, and along the way we've borrowed a few tricks from the animals, too.
When you put on a jacket or snuggle under the covers, you feel warm. Why? Because your coat or the blanket act as insulation, trapping the heat your body produces. Your body uses the food you eat as fuel to stay warm. If you run or jump around, you feel even warmer. Active muscles burn more fuel and produce more heat. That's why you shiver when you're cold. By shivering, your body is doing its best to get your muscles moving and warm you up. Birds, chipmunks, and even bees shiver to keep warm.
The most imporant part of your body to keep warm is your head. Even in the coldest weather, your brain needs lots of warm blood. That's one reason why your feet and hands get cold—your body is sending heat to your brain. If you put on a hat, you will find that your feet and hands get warmer.
A bird's feathers are great insulation against the cold. Outer, or contour, feathers block the cold wind. Nearer the skin, soft down feathers trap a layer of warm air that keeps the bird (or you, if you have a down coat) nice and toasty. As temperatures drop, the down feathers fluff up to trap more heat. Fur works the same way. A bear's winter coat of coarse hair and its thick undercoat are ideal for trapping air and heat next to the skin.
Many animals also need to stay dry to stay warm. Think of how good it feels to get wet on a hot day. That's because water carries heat away from your skin as it evaporates, making you feel cooler. But on a winter day, you don't want to lose any heat. When an animal gets wet, its fur slicks back close to its body. The fur's not fluffy anymore. It can no longer trap a layer of warm air. Think of your down coat. If it gets wet, it can't puff up with warm air to keep you comfortable.
Some animals, such as sheep and ducks, have oil on their fur or feathers to help keep cold water away from their skin. What about polar bears, seals, and whales that swim in icy waters? Lots of blubber is the answer. A bowhead whale can have a layer of blubber up to 20 inches thick. Under their thick fur, polar bears have a four-inch layer of fat to keep the cold out.
A polar bear has another secret. Its hairs are really transparent, not white. They're hollow tubes that let warm sunlight reach the polar bear's skin. Air trapped inside the tubes warms up, too, and provides good insulation. What color is the polar bear's skin? Black. (Really!) Dark colors absorb heat better than light colors (try touching a black car and a white car that have both been sitting in the sun). The polar bear's fur looks white because of the way light reflects off its clear hairs.
Getting through the winter is hard for everyone. Not only is it cold, but food is scarce. It's easy to go hungry. Staying warm is especially hard for small animals, since they don't have as much fat as larger animals. Many smaller animals have to keep very active to stay warm. And to keep active, they need a lot of food. If they don't eat, they will run out of fuel and heat, and they will die.
Some animals prepare ahead of time. Squirrels busily bury acorns in the fall (they eat about 40 pounds of acorns during the winter). Other animals don't store food. The tiny kinglet, a bird less than two inches tall, needs lots of energy to keep its body warm. It eats almost constantly to stay alive.
Bears, chipmunks, and groundhogs stuff themselves with so much food in the summer and fall that they can take winter off—they hibernate. Groundhogs eat and eat until they get so fat they can barely walk. The fat helps to keep them warm and provides energy during the long winter. While hibernating in its burrow, a groundhog seems almost dead. It hardly breathes—taking a breath just once every five minutes. Its body temperature drops to just above freezing and its heart beats only four times a minute—compared to 80 times a minute when it's awake. This way, it needs very little energy to stay alive and comfortable until it emerges from its burrow in spring.
A grizzly bear digs a deep den and lines it with moss, grass, and soft branches when it's time to hibernate. Its body temperature barely drops, and its heartbeat and breath rate stay about normal. But for months, the bear doesn't eat or drink—or go to the bathroom. Grizzly bears do give birth while they're hibernating. The tiny babies—usually two—stay safe and warm in the den.
Beaver lodges seem to use the igloo principle—a house in the snow will keep you warm.
A few animals really chill out in winter—they freeze! Most animals would die if they froze. Sharp crystals of ice in the blood would cut and destroy their living cells. But woodfrogs make a kind of chemical—like antifreeze in a car—that protects their cells. In the spring, they thaw out, ready to hop again.
Finding shelter in winter can be easier than finding food. Many animals dig burrows in the snow, which is an excellent insulator. The frozen crystals act like a blanket to keep fierce winds out and body heat in.
If you could look under the snow in the northern forests, you would find a world of activity. A ruffed grouse makes snow her home when temperatures drop at night or during a storm. Mice and other small animals live all winter under the snow, searching for insects and other food. (But foxes and owls have good ears to hear them, and can crash in on their snowy tunnels.)
People, of course, sometimes make homes out of snow, too. What's it like inside an igloo? Warm enough that the walls need to be lined with animal skins so that they don't melt. The heat comes from human bodies, and usually there is a small fire pit with a vent in the ceiling to let the smoke and stale air out. To keep out the wind, a tunnel leads to an underground entrance. The tunnel dips to act as a trap for cold air, which is heavier than warm air and acts as a block to keep the warm air up in the igloo. Inhabitants might sleep on a raised bed—higher means warmer.
People build the most elaborate shelters of all animals, but until recently, our houses did quite a poor job of keeping us warm. Before there were windows with glass, people could only close the shutters to block out the worst of the cold air. When the winter winds roared, it was both cold and dark inside. All of the heat came from a fireplace, but any spot that wasn't right near the fire was chilly. Throughout most of human history, you could expect to wake up seeing your breath on a cold morning. Even worse, no one had indoor plumbing, so to use the outhouse, you had to get your boots and your coat and go outside. Brrr!
Castles, made of stone, were colder than igloos, unless you were standing right by the fire. Tapestries were hung on the wall for warmth—but kings and queens didn't wear all those royal robes just for looks.
An igloo is usually temporary housing for a hunting expedition. Two skilled people can build an igloo in about an hour.
The igloo's entrance curves down, providing a space for heavier cold air to collect and allowing warm air to rise into the igloo.
To learn more about how animals survive the cold, read:
- Do Not Disturb by Margery Facklam
- The Seven Sleepers by Phyllis S. Busch
- Why is a fire in a fireplace a poor method of heating an area?
- What methods have people developed to heat their homes? Why are these more effective than fires in fireplaces?