Gearing up for a long winter ahead
Vail, CO Colorado
With the onset of our first official snow fall, our brains begin to shift gears. The days of rafting and mountain biking fade into lingering memories of summer and the thoughts of floating through knee-deep powder and picking the perfect line through the aspens and evergreens come to the forefront of our minds.
As our brains begin to gear up for the winter season ahead, we have many things to do in order to prepare ourselves – get out our down coats and boots, wax and edge our skis, and make sure our snow pants still fit. We are not the only ones getting ready for the long winter ahead. Rather than gearing up for playing in the winter wonderland that will soon surround us, black bears are getting ready for a long winters nap. These local mammals are currently making a final ditch effort before entering their winter lairs from which they will not appear for the next five months.
Currently foraging up to 20 hours a day, these hungry bears will consume up to 20,000 calories each day. That is the equivalent of eating 30 cheeseburgers with the works from any fast food restaurant! I would not recommend that for anyone who still wants to fit into his or her snow pants. Good thing bears don’t wear pants.
Black bears are opportunistic foragers, eating whatever they can find, primarily any remaining berries, nuts, seeds, leaves, roots, and other vegetation. They will also scavenge from the carcass of prey that was taken down by another predator or go for the easy target – our trash cans (which is not a safe option for either humans or bears). According to the Colorado Division of Wildlife, until bears hit the hay in mid-November, they can gain 30 pounds per week and add an additional 4 inches of fat to their bodies. This additional weight will provide bears with the warmth and fat reserves their bodies require to make it through the winter.
Once the black bears have gathered sufficient fat reserves, they then begin to determine the location of their winter lair. Their dens are typically found in burrows, caves, hollowed-out trees, and in rock crevices. Bears will form a nest inside their chosen den with leaves, twigs, and other plant material. In addition, their fur thickens into a very warm winter coat.
Gathering of food and locating a winter lair are crucial for the survival of the black bear through the winter months. Because food sources are sparse during the cold months ahead, black bears have adapted to enter a state of torpor through the winter. This is similar to hibernation, but contrary to popular belief black bears are not true hibernators. Yes, they do sleep through the winter, but there are some distinct differences between hibernation and torpor.
Hibernators tend to lower their body temperatures and heart rates quite a bit more than animals entering into a state of torpor. One example of a local true hibernator is the yellow-bellied marmot. When a marmot hibernates it drops its heart rate from 80 beats per minute to 4 or 5 beats per minute. Their body temperature drops to 39 degrees Fahrenheit. Both of these changes happen relatively quickly upon entering hibernation. However, when a black bear first enters into torpor, its heart rate only drops to 45 beats per minute before plummeting to 8 beats per minutes a couple of months into their winter slumber. While true hibernators lower their body temperature to just above freezing, the black bear only lowers its internal temperature to about 88 degrees Fahrenheit, merely 12 degrees colder than their summer time temperature. Because of their size, black bears would not survive the winter lowering their body temperatures to just above freezing.
Another difference is activity throughout the winter. While true hibernators enter into a much deeper sleep than animals in a state of torpor, they will wake up periodically to eat food from storage and to relieve themselves of any metabolic waste. This arousal depletes hibernators of much of their winter fat reserves. Black bears on the other hand, are much lighter sleepers and are able to wake up if disturbed. If you happened to come across a bear in torpor, there is a good chance it would wake from its slumber after several minutes. Since it does not have to raise its body temperature as much, it does not require as much energy to wake up. If you stumbled upon a hibernating marmot however, it would be in such a deep sleep you could punt it across the alpine tundra like a football. Again, I do not recommend this as the marmot would eventually wake up very confused.
While they do not eat, drink, or go to the bathroom during the winter months, female black bears will wake up briefly to give birth to their young. After licking off their newborns, females go back to sleep and the blind cubs instinctively nurse from their mom and snuggle in her fur to keep warm until they are able to leave the den together once the spring rolls around.
As the snow begins to fall keep in mind that all living things, including ourselves, encounter challenges in order to survive the cold and harsh conditions of winter. While black bears are making their final push towards torpor, be bear aware! Stay observant while hiking trails so you do not startle foraging bears and be sure to secure your trash inside or in a bear proof trash can. These things can help keep both humans and bears safe and ready for the long, snowy winter on the horizon.
Beth Garrison is the curriculum specialist for Walking Mountains Science Center. When she is not developing curriculum, she can be found daydreaming about powder days.