
Maine’s black bear cubs are born in dens in January and February. Twins are an indication that their mother had sufficient fat reserves entering hibernation. Photo courtesy of Paul Cyr
It’s February 2010 and I’ve snagged a coveted spot on a field trip near Moosehead Lake with Randy Cross, Maine’s chief bear biologist, and his research team. We’ve been snowshoeing in three feet of snow for an hour in a picturesque spruce-fir forest when Cross raises a hand for us to stop.
Holding what resembles an old-fashioned television antenna high above his head, he rotates 360 degrees on his snowshoes. A radio receiver, attached to his waist and connected by a wire to the antenna, emits a steady beep. “We’re near the bear’s den,” Cross whispers. “We need to spread out and move as quietly as possible.” Several days earlier, Cross told me not to wear metal snowshoes or Gore-Tex clothing. Both make too much noise.
Shanna Wilson, a Unity College volunteer intern student, signals the den’s location by waving her arms and pointing in the direction of a nondescript snow mound. It’s her second den discovery in consecutive days. She has a nose for locating bears’ dens, and an eye on my vintage wood and rawhide modified bear paw snowshoes. “My grandfather had identical snowshoes,” she says. “If you decide to sell yours, please contact me.” I’m unsure if it’s a compliment or unintentional age insult.
The bear crew lays out a dark gray wool blanket, a new radio collar for the sow, vials for drawing blood, a weight scale, tranquilizer drugs and syringes. “OK,” Cross says softly, “we’re ready. Time for the mole to do her thing.”
The mole is Lindsay Tudor — a slender state biologist — nicknamed for her ability to squeeze into tight den openings to see the bear and gauge its weight, critical information in calculating the correct dose of sedatives. Wearing a miner’s headlamp, she enters the den, quickly resurfaces and reports, “The sow weighs about 200 pounds and has two newborn cubs.”
Cross fills a syringe and attaches it to the end of a five-foot aluminum pole called a jab stick. Inside the syringe is a plunger which, on impact, pushes the sedative into a bear’s muscle. With only the pale-yellow soles of Tudor’s Sorel boots showing, she again dives headfirst into the den with the jab stick and pops back out seconds later.
Several minutes later, the drugged sow is dragged from the den and laid on a mesh net and weighed. To keep the cubs warm, Tudor hands one each to Wilson and me. Following instructions, I place the cub inside my buttoned coat with only its head exposed. It starts bawling like a newborn baby, causing Cross to pause from attaching a new radio collar to the sow.
“You’re not holding the cub correctly,” he mildly admonishes me. “Turn it so its head rests on your shoulder. Cuddle it like you would a human baby.” With its cold nose buried in my neck, the cub immediately stops crying.

Randy Cross, Maine wildlife biologist (now retired) and former head of the state’s black bear study, is holding two cubs while their mother is being fitted with a new radio collar. Photo courtesy Paul Cyr
“Sows,” Tudor informs Wilson, “are usually wide awake when I crawl into dens. Their jaws snap in a threatening manner but they’re mostly bluffing.” During her long career as a mole, a bear has bitten her only once, seriously enough, though, to require an emergency room visit.
The air temperature hovers around zero — the lower limit of what Cross considers safe conditions for black bear work — but inside the bear’s lair it’s a balmy 32. A month ago the sow’s twin eight-inch cubs weighed eight ounces at birth and grew quickly, suckling teats on the sow’s sparsely furred underside. Snuggling against her skin, cubs maintain a body temperature of 88 to 98 degrees. Had the sow been unable to store sufficient fat reserves the previous fall, her fertilized eggs would have been aborted.
“Radio collars,” Cross reminds me, “help us better understand bears.” He rattles off important findings: “Some of our radio bears live well into their late 20s. Cubs have a 50 percent chance of reaching their first birthday — starvation being a major cause of death. When bears reach age 2, though, their survival rate jumps to 90 percent.”
Maine’s black bear study — the oldest continuous one in the country — has shed light on a previously poorly understood, reclusive forest dweller. Male bears, called boars, lead solitary lives except during the summer breeding season. Family groups, comprised of adult females and their offspring, have home ranges of 6 to 10 square miles. An independent boar’s home range is about 100 square miles. As 2-year-olds, males develop wanderlust, traveling 100 miles or so before establishing their own home range.
Female cubs also spend two winters with their mom, becoming independent in spring when she enters estrus. “As a sow’s independent daughters mature,” Cross said, “they establish their own home ranges, often near their mother. I’ve seen daughters with cubs visiting their mom with her cubs.” Think of it as a family reunion, minus papa bear.
Onset of hibernation is dictated by food availability. When northern Maine’s forests produce a fall bumper crop of beaked hazelnuts and beech nuts — once every two to three years — bears postpone hibernation until November or December to gorge on the fat-laden nuts that provide foraging bears with 20,000 calories a day. In years of food scarcity, bears will den in early October.
By April, 4-month-old furry cubs, with dark-blue eyes and oversized paws, emerge from dens on unsteady legs to greet a strange new world. In the four months after their birth, cubs will balloon to six pounds. Their lactating mother, though, sacrifices 33 percent of her weight to aid her cubs’ growth. “Sows with multiple cubs,” Cross said, “often emerge from their winter den as walking skeletons.” For the next 18 months, she’ll gain weight teaching her cubs to forage, escape danger by climbing trees, and how to build a day nest in the crown of a tree.
While Cross’ team is preoccupied collecting biological data, I borrow Tudor’s headlamp and play mole by sticking my head inside the sow’s tidy 5-by-5-foot den, which consists mostly of a deep bed of balsam fir needles. It resembles a snow shelter a child might construct in a backyard.

Bear cub being comforted by a member of the state’s bear research team while its mother is being weighed. Photo courtesy Paul Cyr
After administering a drug to reverse the effects of the sedative, the sow is lowered back into the den and the cubs placed on her belly. While waiting for the sow to regain consciousness, Cross shares more of his knowledge from handling and monitoring 3,700 bears during a four-decade career. “For most of Maine’s wildlife,” he says, “winter is the deadliest season. But bears are the exception. Fewer than one percent of Maine’s estimated 30,000 black bears die during the winter.”
With large bodies, high body temperatures and thick pelts, bears are the most efficient hibernators in North America. Hibernation is an evolutionary strategy to survive winter when food and water are in short supply. To conserve fat reserves from October to April — when bears don’t eat, drink, urinate or defecate — their metabolic rate drops by 50 percent. By contrast, chipmunks and woodchucks, whose hibernating body temperatures hover around 40 degrees, must awaken every few days to raise their temperatures to 94 degrees. Not so with bears.
“Bears live on fat reserves for about six months,” Cross says as we leave the awakening bear and her cubs. Their cholesterol levels more than double in winter, which would be lethal in humans. And yet bears suffer no hardening of the arteries, no formations of gallstones, which, in humans, comes about by an imbalance in the chemical makeup of bile in the gallbladder. A bear’s liver produces a bile fluid called ursodeoxycholic acid, which prevents gallstones. The accumulation of urine does not cause urea poisoning as it does with us. Instead, hibernating bears convert urea into nitrogen, which is then recycled to build protein. That explains why hibernating bears emerge after a six-month sleep without losing muscle or bone mass, although they’ve lost considerable weight burning body fat.
In the fading late afternoon sunlight, we snowshoe back to our vehicles amid the sights and trilling songs of courting white-winged crossbills. The end of a magical day in the Maine woods is about to get better for Wilson when Cross pays her the ultimate compliment: “You pinpointed the last two dens. Keep it up and one day you’ll be a mole on a bear crew.”
Ron Joseph is author of Bald Eagles, Bear Cubs, and Hermit Bill: Memories of a Maine Wildlife Biologist, published by Islandport Press
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