This content was created by the National Sleep Foundation
Find out what hibernation is, exactly, and how bears' habits change with the seasons.
If asked to describe how bears sleep, most people would probably say something about how they hibernate all winter. That’s true…sort of. The deciding factors in how much these animals sleep are the season and how much foraging for food they need to do.
In the coldest three to five months of the year, bears go into hibernation. But the act of hibernation isn't the same as everyday sleep, because their bodies go through more drastic changes during hibernation. For example, while hibernating, bears experience a reduced heart rate and blood flow, their body temperature falls by about 10 degrees, and their metabolism drops to about half of what it normally is (so they can survive without eating). The bear doesn’t go to the bathroom and rarely wakes up (it will only if something comes into its den). It also loses up to 25 percent of its weight. What do bears choose for their bedroom? Most often they make a den under a rock, in a hollow tree, snuggled under a fallen tree, or in a brush pile.
In the springtime, as snow melts and food sources become more available, bears wake up from their long hibernation. During the next few months, they rarely sleep at all. It makes sense: They haven’t eaten in a long time and are hungry, so they spend almost the entire time looking for food and getting their body weight back to normal.
Once the long days of summer hit, bears split their time a bit more evenly. They nap and relax during the day and spend the nighttime looking for food. When autumn hits, bears see it as a signal that they need to stock up on food before the winter begins. Gone are those summer naps and, instead, bears spend up to 20 hours a day in the autumn eating. That leaves just a handful of hours to sleep.
What about polar bears? Similar to brown bears and grizzly bears, polar bears are usually hunting or sleeping. From July through December, there isn’t a lot of ice for the polar bears to hunt on, so they rest for up to 87 percent of their day. When it’s time for a polar bear to sleep during the spring, summer, or fall, it either sprawls out onto the ground or ice (if it’s warm outside) or curls up in a temporary shelter (when it’s cold outside). In the deep winter, polar bears hibernate just like other bears.