My son loves to play made up trivia games as we drive. This sometime mind-numbing game brought up an interesting question recently. He asked, “Dad, name five animals (he told me I couldn’t use reptiles and amphibians…he is also a cheater apparently) that hibernate”. My first thought was this was an easy question. Struggling through the question, I had to take a roll call and figure out who is missing from our woods at the moment. This edition of the Nine Minute Naturalist will focus on our mammals that hibernate in the winter.

To honor my son’s question, I am leaving out the obviously dormant species in the reptile and amphibian families. Being cold blooded means functioning in cold weather is not really a viable option. I will focus on mammals and the most obvious animal missing from our landscape is the black bear.

The word hibernation often causes confusion when in reference to black bears. True hibernators have a specialized reduction in their metabolism along with several other bodily changes such as lower heart rates, constriction of blood vessels, reduced breathing and lower oxygen consumption. Many true hibernators will drop their body temperatures to near freezing. Black bears, which are not true hibernators, only reduce their body temperature 10-15 degrees during their period of torpor. As a result, they are much more wakeful hibernators and will leave den sites if disturbed or if there is a prolonged stretch of warm weather. No matter if it is referred to hibernation or torpor, bears do enter a period of prolonged physical inactivity. Their preferred hibernation sites tend to be hollow trees, rock cavities, brush piles and ground dens. Black bears in the western portion of Virginia prefer large, hollow trees and have been found as high as 95 feet off the ground. Dens are entered from November to early January depending on food supply and arrival of winter weather. Once the den site is entered, black bears are able to go the entire time in den without eating, drinking, urinating or defecating. Bears may lose up to 30% of their body weight over the winter. The unique ability of bears to awake from a torpor state allows for females to give birth while in den. Newborn cubs do not hibernate but instead nurse and sleep while the mother is in the torpor state. The mother bear will not leave the den until spring when the cubs are able to walk and follow their mother to food.

Another animal whose presence is especially missed as you drive along the roads of Wintergreen is the groundhog. This common dweller of our roadsides and home sites is one of the few true hibernators at Wintergreen. When the weather begins to get nasty, the groundhog finds a den and stays put until favorable conditions return. Their heart rate slows to 4 or 5 beats per minute to enable a winter long snooze without requiring replenishment of their energy. They generally have a different winter burrow from their summer abode in a more protected spot among trees and shrubs. They spend considerable time making sure the winter resting location is lined with grasses and leaves to maximize the comfort of their sleep. The first groundhogs appear from den in middle to late March at Wintergreen based on the severity of the winter.

The chipmunk is another missing aspect of our local fauna. The chipmunk is much too small to survive a true hibernation. Instead, they go through periods of torpor where they decrease their body temperature from 98.6 to 41 degrees and heartbeats from 350 to 15 beats per minute. They wake every few days to eat and restore lost reserves. Due to having constructed large tunnel systems in preparation of the coming winters, chipmunks don’t have to venture far to reach their food caches prepared for these periodic meals. After eating and defecating, chipmunks resume their winter rest. By early to mid-March our resident chipmunks are back to scurrying across our landscape.

Another true hibernator is the bat. While it is true that some bats greet winter weather by migrating to warmer climates, most of our resident bats enter a true hibernation. Since many of our local bats are dependent on insects, winter is a time to survive not hunt for food. They do this by finding dark, secluded abodes to spend up to six months. Using caves, trees, attics or any other spot they can remain undisturbed, bats enter a state of inactivity that lowers their body temperature, heart rate and metabolic rate. Bats decrease their energy costs by 98% as they live off of fat stores. When they emerge from hibernation their bodies have undergone extreme change. They lose up to a quarter of their body mass during this torpor period. They will emerge from hibernation when the weather warms and prey become available.

The winter of 2022 has been quite rough so far and many are envious of our hibernating creatures as they sleep the winter months away. Although frigid outside, our days are getting longer and soon the footprints of wandering bear or the head of a groundhog peaking over the side of the road will grace us as we wander the Wintergreen environment.