How do bears survive the winter in hibernation without dehydrating? — Mike, Stockholm, Sweden
Marshall Brain Answers:
Many different mammals hibernate. In some species, body temperature can drop down near the freezing point. Heart rate and breathing rates slow way down as well.
Bears do not hibernate nearly that deeply, but their body temperatures do fall and metabolism slows down quite a bit. In this state, bears can go up to 6 months without food and water, and without needing to use the restroom.
Bears do it by burning off about a pound of fat a day. A pound of fat contains 3,500 calories. The process of burning the fat also creates water. Bears then recycle the nitrogen in their urine to create protein. When they come out of hibernation, bears are much lighter and very hungry, but they have lost no muscle mass.