You may have noticed less evidence of black bears out and about on the mountain now that late fall is in full swing and the delicious insects, small mammals, berries, grasses and root plants have disappeared or hardened off (gone brown and dormant). After feasting for weeks on calorie-rich foods to gain as much weight as possible, Anarchist’s bears have started to hole up for the cold, snowy winter months ahead.
With all the fires the past few years, bears, like other large wildlife, needed to roam further, and often into residential areas, to find sufficient calorie-rich food. Some bears will move to lower elevations in the fall to take advantage of the apples and grapes that are easy pickings.
Did you know that hibernation in black bears is different from ‘true or deep hibernators’ like rodents (ground squirrels, chipmunks, marmots) and bats? In true hibernators, the animals sleep so deeply that they are almost impossible to wake up – their heart rate and respiration drop drastically, and their body temperature drops to close to the ambient (outside) temperature. The onset and duration of hibernation, and activities leading up to and following this period, are genetically programmed in black bears based on things like regional temperature and daylength and food availability, all of which differ across North America. Young male bears often roam longer than adult bears or young females before heading to sleep. Teenagers!
The reason black bears hibernate is likely to conserve energy when food sources aren’t readily available and the weather turns cold. During hibernation they won’t eat or drink for extended periods of time, their body temperature lowers slightly, and they don’t move very much. This behavior can last as long as 100 days. In milder climates like on the coast, black bears may choose not to hibernate or only sleep for short periods of time if there is sufficient nutritious food available.
So what happens during hibernation?
Come October/early November, black bears start looking for a place to lay low for the winter months. While they typically do not return to the same den site every year, if a suitable ‘once used’ site is found – well, why not… A good den site could be in a pile of rocks or rock crevice, a large brush pile, a hollow in a stump or a standing or downed tree, or a shallow hole dug into the hillside. Dens are usually only a few degrees warmer than the ambient and soil temperature, so a bear’s main protection from the cold is its fur and body fat.
Black bears are generally solitary throughout the year, with the exception of a mom with cubs. Cubs born the previous winter will hibernate with mom and be pushed out on their own come spring. The only time adult males and females will be seen together is in late May through June when mating occurs. Female bears have a built-in survival adaption called ‘delayed implantation’. This means that the embryo doesn’t implant in the bear’s uterus until fall, and only if she has gained enough body fat through the summer and fall to get her through the winter months (https://www.ontarioparks.com/parksblog/bears-hibernation).
Six to eight weeks after the embryo has implanted and sometime between mid-January and late February, female bears give birth to one to three blind, nearly hairless cubs that weigh less than a pound. Mom will doze off and on for the rest of the winter as her babies feed, grow a fur coat and get chubby and cute.
Because black bears aren’t true hibernators, its important to remain diligent when enjoying the backcountry during the winter. An early wake-up call can be lethal for someone who inadvertently stumbles on an occupied den and for the bear(s) occupying it. It requires a lot of energy for a bear to wake up during hibernation and this kind of surprise won’t be well received. And, if it’s a mother with newly born cubs, depending on the type of disturbance, she can choose to abandon the den and her cubs.
During hibernation, black bears don’t eat, drink, urinate or poop, and they will lose between 15 to 30 percent of their fall body mass. Talk about a weight loss program!!!!! This explains why bears are so darn hungry when they come out of hibernation in the spring. Remarkably, a bear retains most of its muscle and internal organ mass and all of its strength. This is possible by utilizing the nitrogen contained in urea, a by-product of fat metabolism, to synthesize proteins. Bears are also able to recycle their own water all winter, helping to avoid dehydration and kidney failure. While this self-contained system sounds awesome, come spring black bears need to seek out native plants like skunk cabbage that acts as a laxative to help remove all the poop that has built up in its intestines over the winter. So, if you’ve always wondered if a bear does in fact poop in the woods, well HECK YEAH!
Adult male black bears are typically the first leave their dens in the spring, followed by females with year old cubs and then moms with newly born littles.
Interested in reading more about black bears and hibernation, see the following links: