Time to Go to Bed
by Josh Palumbo, Forest Management Coordinator
I welcome you to The Nature Foundation at Wintergreen’s attempt to bring some nature and knowledge into your home. The Nine Minute Naturalist borrows from NPR’s lovely 90-Second Naturalist podcast. Since we all have a bit more time on our hands, the goal is to take something that is happening out in our environment and stimulate your brain for roughly nine minutes. Don’t let something as “minor” as a quarantine to keep you from learning. I hope you enjoy!
While the symbol of the resort and The Nature Foundation is a lovely wintergreen plant, our mascot would undoubtably be the black bear. Despite being a constant presence around our homes and on the trails, the black bear is about to make itself scarce. As cold weather begins to bombard us from the cold north, black bears are about to begin their winter rest. This edition of the Nine Minute Naturalist will examine the hibernation of 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.
A period of preparation is vital for every black bear. In order to prepare for a long torpor, the black bear must store fat in volume. Bears will seek to gain 1-2 lbs per day during the fall in order to prepare of the winter. The key attribute for successfully making it through the food drought of winter is acorns. During heavy acorn mast years, bears will gain up to 100lbs in the fall. When acorn production is light, black bears will seek other sources such as apples, cherries, peaches and cultivated corn. As the food supply dwindles and the cold weather arrives, bears begin to head to den sites.
The preferred den 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.
The hibernation period comes to an end for males from mid-March to mid-April and in early May for female bears with cubs. When bears emerge from their den, quenching hunger is their main focus. Spring is not the ideal time to be starving and it causes the bears to frantically search for food. Insects and grubs are a preferred protein source in early spring. Bears will feed heavily on emerging shoots of grasses, leaf buds, and skunk cabbage. Spring is also a time they will be active predators. Baby deer fawns make a desired meal if they can be found. It is also a prime time for bear human interaction. It is essential to monitor your behavior around your house by mid-March. Once bears leave the den they are looking for whatever they can eat and your house is as good a source as any other. Make sure bird feeders are put away by April 1, but it may need to happen sooner depending on your location and the weather.
The time is coming for bears to go to bed for the winter. While this allows for homeowners in bear country to be less diligent with food sources, keep in mind that bears are not beholden to set times or parameters. The bears’ inactivity can end at any time, and we need to be prepared to alter our behavior in response.