The basic answer is that they go into a light form of hibernation referred to by scientists as “super hibernation“. But this process is not as simple as taking a long nap and waking up in the spring, ready to go. Black bears go through many stages of metabolic changes to adjust to the barren winter conditions, starting with intense feeding cycles. In the summer, bears gorge heavily on nuts and berries and will occasionally hunt fish or small rodents, building up four to five inches of body fat by the fall season. By the time mid-November rolls around, food sources become sparse and genetic signals tell the bears that it’s time to start looking for a den.
In an attempt to conserve their energy, bears’ metabolisms slow down significantly. Their heart rates drop to between 20-40 beats per minute, and sleep begins to consume most of their day. Body temperature drops as well, but still remains relatively high at 88 degrees. This ensures that, in case of danger, bears can become fully alert to protect themselves. It is this particular trait that separates bears as “super hibernators” from true, deep hibernators, which can drop their body temperatures much lower. By late November, bears have made themselves cozy in a den and are getting ready to hibernate.
Where do cubs fit into this picture? Mating season is from May to July, but black bears have a unique trait: right after the egg is fertilized, development pauses until fall. If the mother is in healthy condition and was well-nourished during the summer, the embryo will begin to develop and the cubs will be born around January. Even though the hibernating female will sleep through labor, the cubs’ instincts will keep them close to their mother for warmth and fat-saturated milk. This process ensures that in the spring, the cubs will be strong enough to protect themselves from predators.
During hibernation, eating, drinking, urinating, and defecating cease completely. Even without needing to perform bodily functions, bears still burn around 4,000 calories a day, which depletes most of their body fat. Oxygen consumption, breathing, and blood flow decrease drastically, so it’s no wonder that they need an adjustment period when they awaken in April. During a period of two to three weeks in early spring, food is still limited and their weakened bodies are adapting to being awake, so consumption remains quite low for that time. Once their digestive and respiratory functions have returned to normal, their eating habits pick up again, which usually coincides with the arrival of consistent warm weather. Awake and hungry from the long winter, black bears are ready to repeat the cycle, maybe this time with a few cubs tagging along!
Looking to do an overnight backpacking trip in the Adirondack High Peaks region? Learn more about how to use a bear can and where you can rent one from us. Backpackers are required to carry bear cans in the Eastern High Peaks region between April 1st and November 30th.
A special thanks to Larry Master for giving us permission to use his photos. Check out his work at www.masterimages.org/home.html
Further reading on black bears:
Denali Education Center – https://www.denali.org/denalis-natural-history/black-bear-hibernation/
SUNY-ESF – https://www.esf.edu/pubprog/brochure/bears/bears.htm
New York State Department of Enviromental Conservation: https://www.dec.ny.gov/animals/7225.html