Wildlife Wednesday — Hibernation

Torpor, hibernation, brumation, true hibernation and even super hibernation. These terms can be confusing and often misinterpreted. In fact, they all exist on a continuum of torpor and reflect a reduced metabolism, body temperature, respiration, and heart rate. Torpor is the most basic term and can last for periods of hours to several days. Hummingbirds may go into a state of torpor to make it through a chilly night while a chipmunk may go through bouts of torpor to make it through the winter. Brumation is a similar condition seen in ectotherms, animals like snakes and lizards that cannot internally regulate their body temperature. True hibernators greatly reduce their metabolism, heart rate and respiration, as well as body temperature. Then we have the super hibernator, like the Black bear. Although their body temperature may drop just a few degrees they can go months on end without waking. That means no eating, drinking, defecating, or urinating -- amazing!

The Wyoming ground squirrel has the longest hibernation of all. Not only do they sleep away the winter but they also miss the fall! Wyoming ground squirrels generally enter their dens from late July to September and don’t emerge until late March or April! Like other ground squirrels their hibernation is not continuous but includes brief periods of arousal to pee and poop.

The Western Terrestrial Garter Snake, the only snake in the Estes Valley, goes dormant through the cold months. They rest deep in burrows of other animals, crevasses, or tree stumps that stay above freezing. As ectomorphs their body temperature is the same as the ambient temperature. During brumation their activity level drops so much they don’t need to eat at all and their digestion comes to a halt. If the temperature gets warm enough, however, they could emerge even in winter.

There is some controversy if the Least Chipmunk hibernates at all. They winter away in long tunnel systems. There they go dormant for periods of days at a time curled up in a ball to reduce surface area to conserve heat. But they are prepared, creating some chambers in their burrows for food they stored away and using others for bathrooms.

The Yellow-bellied marmot is the largest of the true hibernators. They are able to drop their body temperature to just a degree or two above freezing. Marmots do not collect and store food for the winter so they rely on stored body fat to fuel them through the cold months.

Bears earn the prize as super hibernators. While their body temperature drops only a few degrees, their respiration drops to a single breath or two per minute and heart rate down to about ten. They have the unique ability to do this while avoid taking in or relieving food or water. Female bears even have the ability to give birth and nurse right through hibernation!