Animals can get through winter in all kinds of ways. Cats like to curl up on a cozy couch. Some penguins huddle in groups to create heat. A lot of birds fly south to warmer weather. Perhaps you put on mittens and a coat.

Then there are the hibernators. Some of these animals are bears, skunks, bats, frogs, and salamanders. Hibernation is like a deep, long winter's sleep. But it isn't exactly the same kind of sleep these animals would normally have at night.Hibernation means big changes for these animals and their bodies. The reason they hibernate is to survive chilly winters, the campus veterinarian here at Washington State University.When scientists study hibernating animals, they find that these creatures have slower heartbeats than normal. A lot of animals can go without food for months at a time. Many don't even have to wake up to go to the bathroom. The hibernating grizzly bears here at WSU wake up for about 15 minutes each day. They go for a quick stretch, paw their straw bedding, and rest again.A lot of bears will spend months preparing for hibernation. While we were getting ready to go back to school, some animals were already stocking their food supply. Some animals stored their food in trees or burrows. Bears store food in their own bodies.Researchers at WSU are learning a lot about bear behavior, including how they can survive with such a slow beating heart and so many extra pounds of fat. This year's biggest bear, John, weighed in at 620 pounds. As he hibernates, he will lose fat. In spring, after he uses that stored up energy, he'll be about 500 pounds. Researchers are using what they learn about bears to help us understand more about heart diseases and obesity in humans, too.Grizzly bears are big hibernators. But other kinds of bears have different techniques to survive chilly temperatures. Some panda bears migrate to warmer conditions.Some polar bears can hibernate for about 8 months. They build dens and have other adaptations like thick blubbery fat and extra fur to help them survive in the cold, too.And while some animals have adapted to survive chilly winters, other animals need to survive hot summers. This is called estivation. Instead of storing up food and staying warm, these animals save up water and try to escape the heat.Ask Dr. Universe is a science-education project from Washington State University. Send in your own science question at

http://askDrUniverse.wsu.edu.