By now most grizzly bears are snug in winter dens, safe at last from poachers, big game hunters, and other dangers. Last week, to the relief of her many fans, Number 399, the rock star grizzly matron of Grand Teton Park, was seen with her two yearling cubs making their way back towards her denning area along Pilgrim Creek. She and her family had stayed up later than most grizzlies because they could feast on the abundant remains of elk killed by hunters in Jackson Hole. Once again, this 21-year-old veteran mom had miraculously survived a landscape bristling with guns as well as other hazards that come with her life strategy of living close to people.
What does the next four to five months of life look like for her and other grizzly bear moms? Let’s peer into her lair and find out.
In the darkness below the snow, we find miracles and mysteries. I like the fact that, despite industrial-scale research, hibernation remains magical and elusive. Wild animals will always defy circumscription by the human intellect – and throw us back on heart, soul, and imagination.
There are some things that we do know about hibernation. Bears don’t eat or drink or excrete waste for between 150 and 180 days. (If it were you or me, we would have died after just a few days.) But when bears crawl out of their dens in the spring, they are specimens of health. They don’t lose much bone strength or lean muscle mass, even though they may lose as much as 30% of their fall weight. And their kidneys, liver, and hearts don’t fail.
Unlike deep hibernators, bears are not unconscious during their winter slumber. Nor, like ground squirrels, does their body temperature plummet to freezing. Which is why mother bears can give birth in the dead of winter to a cub or two, each the size of a teacup, which she groggily nurses in her den until sometime during April or even May. Her milk has the highest fat content of any terrestrial mammal, and so cubs grow super fast – from about a pound at birth to roughly 20 pounds at 12 weeks when they leave the den.
How does a mother bear pull off this incredible feat? Part of her secret involves obesity. Gorging on foods ranging from meat and moths to ants and whitebark pine seeds, a grizzly bear packs on several pounds a day during her late summer and fall hyperphagic feeding frenzy. Amazingly, she consumes roughly 30,500 kcal of digestible energy every day during the fall, compared to the approximate 2,700 kcal that a 200-pound couch potato human would need to survive.
Although grizzlies mate during late spring, the female’s fertilized eggs do not implant till she dens. If she is not fat enough to pull off a successful pregnancy in the den--which could kill both her and her cubs—she spontaneously aborts. Miraculous or what?
Her choice of a den site helps boost her chances of success. She digs her den at higher elevations and on north-facing slopes where snows pile deep enough to cover the entrance hole and provide not only good insulation but also absolute safety from predators. Often taking advantage of a natural roof provided by boulders or tree roots, she makes the den a tad larger than her body for a snug fit.
The Miracle of Hibernation
What happens next to the bear is physiologically both fascinating and confounding. Researcher Dr. Lynn Rogers provides an intimate although perhaps intrusive peek at the life of a wild black bear family in their den, thanks to a miniature video camera– complete with contractions, delivery, nursing, baby noises (from purrs and grunts to screams) and, ultimately, the cub’s emergence into the big wide world—by the scruff of the neck.
The potential importance of hibernation is not lost on medical researchers. Scientists have long suspected that the mysteries of bear hibernation, if unlocked, could benefit people with heart disease, diabetes, osteoporosis, and traumatic injuries.
Have scientists gotten closer to unveiling the grizzly bear’s secrets? Yes and no. They are far from realizing the dream of putting people who have experienced traumatic injury into the kind of suspended animation that characterizes hibernation. They hope that by inducing hibernation in someone undergoing a stroke or cardiac arrest, they could buy doctors precious treatment time. So far, the closest they have come is applying cold fluids, internally and externally, to temporarily slow metabolic processes.
Scientists are making more headway divining treatments for human osteoporosis. If we are inactive for months, even weeks, our bones deteriorate to the point we can no longer walk. But bears produce a parathyroid hormone that maintains bone density and strength. Today, some doctors are treating humans suffering from osteoporosis with a manufactured hormone that matches what bears produce.
Researchers have a rudimentary understanding of how hibernating bears avoid diabetes, but not enough for practical application. Even though “healthy” bears get manifestly obese by late fall, they do not get Type 2 diabetes. Diabetes occurs when cells are no longer able to take up sugar in response to infusions of insulin. When humans who are starving or who have uncontrolled diabetes rely on fat for energy, the body cannot handle the toxic byproducts of fat catabolism. Not so for bears. They are able to recycle these byproducts into making more fat. If that is not a miracle, what is?
Kidney function in bears is similarly weird and wonderful. If our kidneys did not excrete otherwise toxic wastes such as uric acid, we would soon die. But get this: bears have microbes in their guts that, during the winter months, convert urea to nitrogen to make new amino acids that are the building blocks of protein. This enables bears to maintain lean body tissue in the comfort of their own dens without eating or eliminating waste. It is no accident that researchers are looking to bears for some answers about how to feed malnourished populations in developing countries with limited access to protein-rich foods.
To scientists, hibernating bears are mind-blowing for yet more reasons. For example, when they implanted a defibrillator in a bear’s heart to measure heart rate during hibernation, the bear’s body forcibly ejected it. Same with implants in its gut. The bear’s basic response to implants of foreign objects is to powerfully reject them. Maybe that is why bears rarely get infections. Researchers are especially intrigued with the possible role of ursodeoxycholic acid, a bile acid named for Ursus (Latin for “bear”) that is elevated during hibernation and could help treat human injuries.
And here is yet another surprise: bears actually stop breathing during hibernation for as much as 25-30 seconds at a time. With lower oxygen requirements, they don’t have to breathe as much. When oxygen levels get low enough, their brain sends a signal to take another breath. And get this: when a bear inhales, its heart rate can increase 800-fold, while a human’s increases only by one-fortieth as much. What athlete doesn’t want to borrow that trick?
Scientists studying bear hibernation are not the only ones who at some point just throw up their hands in awe.
Awe lies at the heart of the relationship between ancient cultures and bears. All species of bear share the ability to seemingly die in winter and remerge in spring with new life. Because of this, bears have symbolized transformation since time immemorial. Seeking the bear’s gifts, we have looked to this creature as teacher, guide, and healer. Today, our use of the bear’s name for sports teams and stock markets is hardly accidental. Moreover, the word “bear” in English shares the same root as “birth,” “breath,” “bury,” and “beer.”
In modern ecology, you hear that the grizzly bear is an “umbrella species.” The health of grizzly bear populations engenders health for entire ecosystems. Ancients had a different way of orienting to the same issue. There is an old story of a bear that goes into her den to dream the world into being each winter. She dreams of antelope and whitebark pine and buffalo. In her imagination, she creates each being and entire ecosystems during the long barren months. When she emerges in the spring, trailed by a young cub, she is celebrated by all the creatures of the earth.
In my gathering of bear stories over the years, I have found only one that truly baffles me. It is the story that legitimizes killing bears as trophies and extolls destroying bears when nonlethal approaches are available for resolving conflicts. This story is the opposite of reverence and wonder. It is about domination, violence, and death.
This utilitarian narrative, which drove the genocides of bears, bison, wolves, and native peoples, survives today in many forms, particularly in western states. Despite harboring the last populations of wolves, bison, and grizzlies in the continental US, wildlife managers in Wyoming, Montana, and Idaho are relentless proponents of hunting these species, ostensibly to control populations – although the best available science shows that grizzlies are self-regulating.
For decades, these managers and their political masters have doggedly worked to remove federal Endangered Species protections for grizzly bears in the Yellowstone (GYE) and the Northern Continental Divide (NCDE) Ecosystems–succeeding in the case of wolves, which are again being slaughtered outside our National Parks. Despite setbacks imposed by a court order in September that restored federal protections for Yellowstone’s grizzlies, state politicians and their regressive allies are not giving up. Last week the NRA, Safari Club, and state of Wyoming appealed the relisting order. At the same time, the state of Montana adopted new regulations designed to facilitate removal of ESA protections for NCDE grizzlies. And we can expect more attempts to legislatively delist grizzlies during future Congressional sessions.
Elsewhere in the country, other states have broadened their financial and political base beyond hunters and fishers. This shift is boosting conservation of nongame species as well as respect for all wildlife, not just species that can be hunted. The explosion of public interest in seeing and photographing rare and iconic wildlife such as grizzlies encourages a similar approach in Northern Rockies states. But here, managers still cling to their traditional “clientele” of hunters, even though the number of hunters afield are in precipitous decline. The stage is set for ever-greater conflict among those with opposing world views about wildlife.
As grizzly bears disappear into high-country dens to undertake the annual miracle of hibernation, we ourselves can pause for reflection. What kind of world will we dream for grizzly bears this winter? What sort of world will grizzly bears wake up to next spring? Will it be a world in which wonder is diminished or renewed?