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| A large black bear near Park Falls lies curled and hibernating inside its den about five feet underground. Patrick Durkin|For the State Journal |
But the veteran logger knew it was no ordinary hole, so he silenced his chainsaw and approached for a closer look. The crusty snow tapering into the hole had a frothy quality -- the kind that whitens eyebrows on sub-zero days.
He knew what that meant, so he knelt atop the hole and peered inside. Less-experienced eyes might glance and mistake the shadowy-black circle for a bottomless pit. The logger, however, let his eyes adjust and recognized a 3-D shape.
He smiled. The old black bear -- a male, most likely -- had made it through another hunting season and returned to the dirt cave to hibernate. The logger and his friend have monitored the den for several winters. This marks the third straight year its occupant is a lone, large bruin, making them think it's an old male.
That's about the extent of the loggers' "research" into this particular bear. They leave those academic endeavors to University of Wisconsin students and professors. These days that includes Professor Tim Ginnett at UW-Stevens Point and graduate assistant Karl Malcolm and Professor Tim Van Deelen at UW-Madison.
Ginnett took over UWSP's long-running black-bear studies in 2001, about a year after his storied predecessor, Ray Anderson, died. Ginnett and his students work almost exclusively with female bears to study their survival rates and reproductive patterns.
They've found northern Wisconsin's bears almost immune to variations in weather and hunting pressure. No matter how dry, cold, wet or warm their environment; and no matter how many hunting tags the Department of Natural Resources issues, female bears in these studies have about an 80 percent annual survival rate. In addition, they nurture about 2.5 cubs to adulthood during each breeding cycle, which occurs every other year.
Ginnett knows this because each winter he and his students crawl into dens where bears hibernate, locate a foreleg on the mother, and inject a sedative into the lean muscle on its lower end. This ensures she won't get irritable while they record information and attach or remove tags or collars that help tell her life story.
Such den work is less complicated when a sow has recently given birth, which usually occurs in early January. Newborn cubs are easy to work around because they weigh mere ounces and quickly gravitate to a nipple to nurse. They'll weigh about 6 to 8 pounds by winter's end and then grow to about 50 to 60 pounds before hibernating the next winter for a second and final time with their mother.
"When you crawl into a den when Mom has three or four yearlings, that's a lot of bear in one hole," Ginnett said. "It's not clear where one bear ends and another begins and it's not easy to tell their head from their rear when they're curled up."
Ginnett said hibernating black bears inhale and exhale two to five times per minute and some have heart rates as low as 10 to 20 beats per minute. They also remain incredibly nimble despite remaining immobile for weeks or months. Some hibernating bears awaken and hit the ground running.
Malcolm said "runners" are usually bears that hibernate among thick grasses or fallen treetops in above-ground "nests."
Because they tend to be less groggy and more unpredictable than bears in cozier dens below ground, they might flee at the first sight or sound of intruders. Therefore, researchers sometimes use dart guns to tranquilize them from a safe distance.
The bears' ability to regain "their form" after prolonged immobility intrigues medical researchers in Madison. How can bears awaken free of bed sores, stiff joints and cramped muscles?
"Human muscles quickly atrophy without activity," Malcolm said. "When people are laid up because of serious illness or surgery, they can barely stand when they're finally allowed out of bed. Bears don't have those problems. Is it something chemical? There's a lot to be learned."
Malcolm's research, however, focuses on the growing bear population in agricultural areas between Highway 10 and the state's northern forests. He's studying how and where yearlings disperse to new range in habitats dominated by fields and fragmented woodlots. Most of these bears - which are monitored with GPS collars - come from dens near Colfax/Eau Claire and Wausau/Weston.
Like the loggers who rarely reveal a bear den's location, researchers also conceal den sites for fear that unwanted visitors will pester the bears. Although hibernating bears might not protest your presence, that doesn't mean they welcome it.
