Most bears hibernate in the winter because the weather is harsh and it is difficult to find food. The only bears who do not naturally hibernate are polar bears.Typically, bears hibernate from December to March. To prepare for hibernation a bear will build a den and eat much more than usual, almost 90lbs of food a day! A den is a secure place in the ground or in a cave where a bear can safely hibernate and store extra food. Before hibernation bears will gain 30 pounds a week. When a bear begins hibernation they go into a deep sleep. During hibernation bears do not eat or drink. Unlike other animals, bears are in a semi-hibernation state and they can come out of hibernation to defend their cubs or den if need be.