Black bears are built to climb. Their prodigious upper body strength, coupled with a unique skeletal adaptation, enables bears to scurry squirrel-like up tall trees in seconds. The ursid shoulder blade is key to this success. A flange-like extension from the rim of the scapula accommodates a specialized muscle attachment that dramatically increases the bear’s strength and leverage while simultaneously minimizing debilitating wear and tear on the shoulder joint.
When confronted by danger, a bear leaps up with full force onto a tree with outspread limbs. It then immediately proceeds to bound up the trunk, flexing and extending the spinal column, which provides some upward momentum while the bear simultaneously shoves with its hind feet and grasps with its front paws in unison. Less urgent climbs are achieved by simply walking up the tree with three-point foot contact at all times. The bear’s front feet are angled out to the side or even behind the tree’s trunk. Hind feet are positioned directly beneath the bear, where leverage and extra traction are achieved simply as a result of the bear’s own body weight pushing the feet inward towards the trunk. Sometimes bears use their teeth and strong jaws to hold onto tree limbs for extra grip while climbing. When descending the tree, a bear looks over its shoulder and climbs down the way it went up. On smaller trees, the hind feet are deliberately wrapped around the sides of the tree; this allows the legs to provide some friction, much as we would do while shinnying.
Bear-climbing sign is obvious on smooth-barked trees like American beech, serviceberry, and aspen. Sign can be harder to detect on other trees, including apple, hickory, and black cherry. To decipher how the bear climbed the tree, inspect the bole for a sequence of parallel claw marks corresponding to the placement of front and hind feet. Position your body the way you would if you were to start to climb. Approach the uphill side of the tree and look for reachable limbs that you would grasp. Look closely for hind foot and front foot claw scars where first steps might have been made. Note that scars made by the front feet are most typically found on the sides of the trunk, or behind it, depending on the size of the tree, and that frontclaw marks are angled as much as 45 degrees because the bear was reaching around the tree when it made them. Hind-claw scars, meanwhile, are always straight up and down since the hind legs were directly below the bear. To confirm ambiguous scars, look closely for black hairs which may have snagged on rough bark, protruding broken branches, or fruit spurs during the bear’s ascent.
Susan C. Morse is founder and program director of Keeping Track in Huntington, Vermont.