Why do brown bears hibernate?

Answer 1

They hibernate in the winter when it is the coldest and food is scarce. Contrary to popular belief, not all bears go to sleep in the beginning of winter and emerge in the spring. Most bears will come out a few times during the winter but go back in to continue to hibernate.

Answer 2

During hibernation, bears need less food. so they hibernate when there isn't enough food available to stay awake.