Bears hibernate during the winter months in most areas of the world. The denning period in YNP is approximately 5 months. For many years bears were not considered to be true hibernators. Mammals considered true, or deep hibernators, such as chipmunks and ground squirrels, experience a drastic decrease in body temperature during hibernation.
Many researchers now consider bears to be super-hibernators.
Respirations in bears decrease from 6-10 breaths per minute normally, to 1 breath every 45 seconds during hibernation. Grizzly bears and black bears generally do not eat, drink, defecate, or urinate during hibernation. Bears live off of a layer of fat built up during the summer and fall months prior to hibernation. Waste products are produced, however, instead of disposing of their metabolic waste, bears recycle it. It was once thought that bears ate roughage prior to den entrance to scour their digestive tract and form a plug in the anus to prevent them from eating any more food that fall.