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Bear Track & Sign Weekend with Sue Mansfield

posted May 22, 2018, 8:28 AM by Jonathan Poppele   [ updated May 22, 2018, 8:28 AM ]
Over the weekend of May 4-6, renowned black bear researcher Sue Mansfield led a group from the tracking club on a deep dive into identifying and interpreting bear sign at her old study sites around Bear Head Lake State Park near Ely. We studied bite marks and scat, examined sun bleached hairs, and even crawled into an old den to further our understanding of one of the largest mammals in Minnesota. Here is some of what we learned...

Dens

Black bear den sites include underground burrows bears excavate or find, inside large hollow trees, under root wads, in caves, under porches, or even in above ground pits they dig. Sue showed us a den site where a mother and her cubs used an old campground's concrete latrine as a den. Black bears may line the den with branches of coniferous trees, grasses, and other vegetation. Female bears generally select more secure sites than males. Also, as bears age they select more secure sites, whereas inexperienced bears might select sites that are more exposed to weather.

After bears put on fat from voracious eating during warmer months, their metabolism slows and they enter the den. In northern Minnesota males males typically enter their dens in September, but even as early as late August, while mother-and-cub families enter in later October to give cubs more time to feed. A female carrying fertilized eggs will give birth in the den. The eggs remain in suspended animation until mid-November or December when the embryos implant in the wall of the uterus. Cubs are born in January or February in the den and nurse.

During hibernation black bears decrease their body temperature by 7 to 8 degrees and their metabolism by 50 to 60 percent. They lose about 20 percent of their weight.

Here is the den site used by Aster during her second and third year. The den was excavated under a mound of tree roots. The entrance angles downward and then flattens. A mother bear and newly born cubs would be cozy. Several of us climbed into the den and found we could curl up at the bottom and be more than 5 feet from the opening.

Scat

Kersey Lawrence once describe black bears to us as "hungry little tanks." Sue Mansfield helped bring that lesson home when she shared her wealth of knowledge and bear scat samples with us. The sheer variety of items in her 20+ samples was astonishing - different seeds, nutshells, vegetation, insects, small chips of bone. Likewise, the videos Sue shared of June and other research bears showed gentle but persistent feeding across a wide variety of foods. They consumed vast quantities of calla lilies, delicately stripped leaves off of stems, nipped catkins and berries from branches broken off the tree, and vacuumed up ant pupae from rotten logs and under stones in an abandoned railroad bed. The sole mammalian casualty was a fawn that could not yet walk.

Sunday morning, we were delighted to find fresh examples in the field. The first scat we found was remarkable for its volume alone: large blunt-tipped ropes of stool exceeding the usual output from a large canid. As we kneeled down and leaned in for a closer look at contents, the fragrance was musky and earthy, not unpleasant. As we picked it apart we discovered lots of plant matter, mostly grasses, and also a few deer hair. Sue remarked the deer hair was unusual - perhaps this bear had scavenged an old deer carcass. And, she encouraged us to take a sample home to sieve it, to see what else might be there. Results of that stool test are still pending! The second scat we found was comprised almost entirely of sunflower seed hulls. That bear was clearly returning from someone's backyard feeder!

Key features for identifying bear scat:
  • Large volume with blunt-tipped segments 1+ inch in diameter. May be loose if bear has consumed fruit.
  • Composition and cohesion varies strongly depending on season and available foods.
  • May contain grasses, nuts and shells, fruits & seeds, insects, and small chips of bone. Less likely to contain deer hair.
  • Fragrance is musky and earthy, not unpleasant or sharp

Bites

It is normal to see wooden signs and telephone posts in Northern Minnesota with gouges in them. It is so common, that many of us had come to think of such damage as simply the way old signs look in the woods. But as Sue sowed us, much of this damage is in fact the marking behavior of black bears. Bears select trees, poles and other suitable objects along travel routes and near feeding areas to mark their presence. Black bears commonly mark trees by standing on their hind legs and rubbing their backs against the trunk. They will also bite the trees--often by reaching over their shoulder while standing against the trunk. The bite marks are particularly distinctive. For some reason, bears are particularly drawn to cedar posts and signs (used so often in the back country because of their resistance to rot) and poles treated with creoseal.

Black bear bites show up as a dot-dash pattern on the trunk of a tree--commonly close to eye level (though they sometimes are much lower, especially on cedar posts and creoseal treated poles). The "dot and dash" are formed by the canine teeth coming together. The lower canine acts as an anchor forming the "dot" and the upper canine drags across the wood forming the "dash." The bite is typically at a shallow angle across the trunk--about 15-30* from horizontal.


After a day-and-a-half in the field, our group ventured into Ely to visit the North American Bear Center--which features a great many videos, exhibits and displays put together by our host, Sue Mansfield. The center also has four resident bears, who we got to see up close during one of the regularly scheduled tours. Seeing the exhibits and watching the bears after a weekend of studying their sign was a real treat, and a great way to cap off a rich weekend in the field. We all extend a warm thank you to Sue Mansfield for sharing her deep knowledge, understanding and love for these animals with us. We are all looking forward to our next opportunity to venture into bear country and see the signs of these amazing animals.