During the winter months, many animals seem to disappear as temperatures drop and the days grow shorter. Some of them migrate, but others hibernate. Hibernation is a state in which animals fall into a deep sleep-like state. The marmot hibernates for up to eight months every year! But it's not just mammals that hibernate. Reptiles such as snakes and turtles also hibernate. While the box turtle hibernates, its heart beats once every five to ten minutes, and it doesn't have to breathe--instead, it takes in oxygen through its skin. When warmer spring temperatures arrive, hibernating animals wake up and go out in search of food to fill their empty stomachs.

Learn more about hibernating animals on the Earth Rangers Wild Wire.

Get facts on your favorite animals on National Geographic Kids.