Blane Klemek column: Bears find a variety of hibernation dens
I've written about black bears many times over the years, including about not only one particular Minnesota black bear, but about her and other black bears' dens.
How a black bear goes about choosing a den is highly interesting. In fact, I'm not sure anyone really knows. Indeed, from curling up inside a cave to crawling into the tangled branches of a brush pile, the American black bears aren't - as it turns out - especially choosy about where they end up spending any given winter.
As most everyone knows, black bears are abundant throughout most of the northern half of Minnesota. In fact, no other North American bear is more widespread than black bears are. Though their former range included forested habitats from Mexico to Alaska and Canada, today black bears occur in about 40 of the 50 states. Their Canadian and Alaskan presence is probably very close to historical abundance.
Minnesota's northern forested regions, including suitable wooded habitats in the central and northwestern parts of the state, support thriving populations of black bears. Even so, observing one is still a rare event. And as I've written in the past, even rarer than observing a black bear is finding a black bear den. Commencing around late October into November through March and into April, Minnesota's black bears hibernate in a variety of interesting and secretive places.
I have been lucky to visit active bear dens each of the past two winters with DNR bear research biologists Dave Garshelis and Karen Noyce to collect important data from a radio collared female bear and her cubs. The black bear, dubbed the "gold-faced bear" because of the extent of her brown facial coloration (just the muzzles are brown on most black bears), had been wearing a collar for a number of years. Outfitting bears with radio collars enables research biologists to learn about the health, reproduction, habitat preference, home range, and much more, about black bears.
Needless to say, I have been thrilled with the experiences of not only helping with the black bear research, but also in handling the sow's cubs. But, as I've also mentioned before, what is also very interesting is the types of dens that the sow had chosen from one year to the next. What's often believed is that bears hibernate in the same dens year after year. This, in fact, is not necessarily the case.
For instance, in 2008 the sow black bear chose a hollow "root-wad" of a wind-thrown balsam fir tree to den inside of. An adjacent tree that the fir tree struck when it originally blew over prevented the balsam from completely reaching the forest floor. Consequently, the balsam's roots did not come out of the ground to create the classic ground depression that a wind-thrown tree's roots typically leave behind. In the case of this tree, its roots remained bound in the soil and, instead, a cavity was formed within.
The sow and her three yearling cubs were all sleeping comfortably inside the root-wad. Once we had removed all four bears, I poked my head inside the cavity and examined the interior with a flashlight. I was surprised by the relative comfort of the den. It was completely dry inside and its floor was covered with grasses that were evidently put there by the sow. The den's odor was not at all unpleasant; I could smell only the scent of vegetation and soil.
The dimensions of the den were no larger than four feet by four feet, probably smaller, and were between two and three feet high. Its entrance hole was small as well, scarcely big enough for an average man to fit through. It was obvious to me that the bear den, with four bears sleeping snuggly inside, was a safe, warm and dry place to spend the winter.
So, one would think, with den selecting skills like this, the sow black bear would have probably chosen a similar, if not the same, den last year, right? Wrong. Her den-site selection surprised all of us, given what we found her inside of in 2008. The two dens were also polar opposites of each other, despite being relatively close in proximity.
As we followed along behind Karen as she tracked the bears' location with her radio telemetry equipment, we all wondered what type of den we would find the bear sleeping inside of, in addition to wondering whether or not she had newborn cubs with her.
We soon found out.
The gold-faced bear chose a "den" in the wide open air. Instead of the snug and dry confines of her root-wad dirt-cave that she and her cubs used the winter before, last winter's den was on the cold ground at the edge of a swamp within a corral of logs underneath the open sky and a few trees. Her den wasn't a shelter of any kind, yet there she was, along with her four newborn cubs, comfortably sleeping no worse for the wear.
Nonetheless, the sow black bear chose the specific site for a reason that only she could have known. She took care in gathering plenty of vegetation to build a soft nest for herself and her cubs. The bed of plant materials included an abundance of grasses, leaves, and ferns. So hidden was she behind the screen of logs that I'm certain that if not for radio telemetry, one would nearly have to trip over the logs in order to have discovered her secret bed.
Unfortunately, the gold-faced bear is no longer outfitted with a radio collar, and so a new research bear is currently being sought in the Bemidji area. In fact, DNR is asking the public to report any known and occupied bear dens to the local Wildlife Office so important black bear research and education can continue.
As such, right now, in forests throughout Minnesota, black bears are sleeping in a surprising variety of places as we get out and enjoy the great outdoors.
Blane Klemek is the Bemidji area assistant wildlife manager, DNR Division of Fish & Wildlife. He can be reached at firstname.lastname@example.org