The way Yellowstone’s wildlife prepares for and responds to winter provides some amazing opportunities to study animal adaptations. Some species migrate to lower elevations or latitudes. Some species are able to stay here due to adaptations. A subset of those, hibernate for the winter, and hibernation is one of the most fascinating adaptations in nature.
Marmots, ground squirrels and some mice here in Yellowstone begin preparing for winter almost as soon as summer begins. A stash of nuts, roots, seeds and other plants will be needed, along with a good layer of fat, just to survive the winter. These animals are considered “deep hibernators.”
When “deep hibernators” den, they quickly fall into a dormant state; their heart rate drops to just a few beats per minute and their body temperature can drop to below 40 degrees F. While they are not easily disturbed, they do wake-up from time to time. During these active periods, deep hibernators eat, drink, urinate and defecate, before returning to a dormant state.
Hibernation is different for Yellowstone’s bear population. By August, they are in an overeating phase called hyperphagia. During this time, bears consume as much as 20,000 calories a day until they enter their den, usually by mid-November.
There is a black bear den I’ve been watching in the woods near here. A bear will take weeks to drop into a deep slumber, but an undisturbed bear can remain that way for months. A bears’s heart rate drops like other hibernators, but their body temperature only drops a few degrees.
This small drop in temperature enables bears to respond to disturbances quickly. Bears never eat, drink, urinate or defecate while denning. All nutrients come from their fat layer. These differences have led many to say bears are not “true hibernators,” which is not true. I have also heard biologists call them “super hibernators,” because of their efficiency.
Scientists have identified an opiate like substance in hibernators that could revolutionize human organ transplants. It is the connections between science, nature and our health as a species that make protecting wild places like Yellowstone so important.