On Thin Ice
Already struggling with pollution, oil drilling and other threats, can polar bears survive global warming's devastating effects?
- Daniel Glick
- Dec 01, 2006
FOR MORE THAN AN HOUR, the solitary polar bear tossed what appeared to be a plastic toy around a frozen lagoon along the Beaufort Sea. Looking through photographer Steven Kazlowski's telephoto lens, I watched as the unusual plaything--a walrus flipper--came into focus. The white-fleeced female twirled the flipper in her teeth, hurled it 10 feet in the air, and watched it land in a watery hole in the ice. She then dove headlong under the frigid water to retrieve the flipper, leaving only the bottoms of her furry hind paws pointed toward the blue sky. Surfacing, she heaved her 350-pound frame back onto the ice edge with a jaw-dropping display of strength, then shook her darkened, water-slicked fur until she was fluffy and white again. As the afternoon light edged toward perfect, the bear lobbed the flipper some more, jumped in the water and repeated the process again and again. Her curious behavior had no possible explanation besides what it seemed to be: a young, well-fed polar bear playing on an autumn afternoon as if she didn't have a care in the world.
Unfortunately, this lighthearted scene showcasing the bear's remarkable adaptation to its icy habitat belies the challenges facing Ursus maritimus, a species heading toward an uncertain future in a rapidly changing circumpolar world. From chemical pollution to oil drilling, hunting to tourism, polar bears are up against an agonizingly familiar series of threats that endanger thousands of species around the globe. But polar bears, which evolved during the late Pleistocene era to survive in one of the planet's most inhospitable environments, must also negotiate an overarching obstacle that uniquely challenges their survival: melting sea ice. Because of global warming, the ice that the bears depend on to supply food and shelter is literally melting under their paws.
Andrew Derocher, a professor at the University of Alberta and chairman of IUCN-The World Conservation Union's Polar Bear Specialist Group, likens global warming's impact on polar bears to the effects of clear-cutting a forest or destroying a desert by building tract homes. "That's essentially what you're doing when you take away the sea ice," he says. "If you have an erosion of the bears' habitat, you'll see the populations erode and retreat northwards."
The flipper-tossing female, which Kazlowski estimated to be four years old (and nearly ready to begin her reproductive life), was coming of age in a region where global warming is no longer hypothetical. In recent decades, scientists have measured Arctic temperatures rising many times faster than anywhere else on the planet, resulting in a reduction in the amount of sea ice, melting permafrost and a host of ecological changes that are affecting everything from riparian ecosystems to animal behavior.
Already, polar bear biologists have recorded strange happenings across the species' range, which spans five countries (Russia, Canada, Greenland, Norway and the United States). For several years, Derocher and biologists Ian Stirling and Nick Lunn from the Canadian Wildlife Service have been documenting that polar bears at the southern edge of their range in Canada's James and Hudson Bays are becoming thinner, with lower reproductive rates and declining body condition. Between 1980 and 2004, the average weight of a mature female dropped from 650 to 507 pounds. Derocher has also detailed unusual pseudohermaphroditism, or females displaying some male sexual characteristics. In other species, exposure to man-made chemicals, especially during pregnancy, has been associated with such unusual gender-bending effects.
In 2004, researchers from the U.S. Minerals Management Service discovered four drowned polar bears in the Beaufort Sea, an unprecedented find among animals that are notoriously strong swimmers and routinely travel long distances between ice floes. Researchers attributed the drownings to the fact that the polar ice cap had retreated a record 160 miles north of the Alaskan coast, meaning the bears had to swim extremely long distances to find solid ice.
And last year, polar bear expert Steven Amstrup, a U.S. Geological Survey researcher, published a shocking study on polar bears "stalking, killing and eating other polar bears" in the southern Beaufort Sea. Although the bears have been known to kill others' cubs, competition for scarcer food may have pushed them toward cannibalism.
Photographer Kazlowski, who is working on a book about the effects of climate change on polar bears, took me to the "bone pile"--a mound of bowhead skeletons left by Inupiat whalers--near the border of the Arctic National Wildlife Refuge (ANWR). Here at the continent's edge sat three bowhead carcasses, with giant vertebrae sticking into the sky and glaucus gulls alighting on the arched, red-stained jawbones. A polar bear female and two cubs tore and gnashed at the frozen baleen and whale ribs.
While the bears fed on the carcasses, Kazlowski and I shivered in the truck and talked about the species' predicament. With Congress once again considering a proposal to allow oil drilling in ANWR, and several offshore drilling proposals already moving forward, the subject turned to the possible effects of industrial activity on the bears. To date, the animal most associated with the ANWR debate has been the caribou. But Alaska's approximately 3,500 polar bears may be even more affected. Proposals to expand oil production, both onshore and offshore, mean that oil spills could soil more ringed and bearded seals (the bears' main prey). Increased industrial and human activity would also impact hunting, mating and denning success with more roads, more ship traffic and more hunting by humans.
Already, persistent pollutants that have worked their way into the Arctic ecosystem are threatening the bears. Long-lasting PCBs flowing from southern climes into Arctic rivers are transported upward through the food chain in ever-higher concentrations. As an apex predator, polar bears are at the top of this chain, and scientists have reported high levels of toxins in the bears, especially in East Greenland and the Barents Sea, which seem to be affecting the animals' reproduction and health.
So far, most polar bear populations remain relatively healthy, the worldwide total having rebounded from a low of about 10,000 animals in the mid-1960s to a current estimated 20,000 to 25,000 bears, most of them living in Canada. A 1973 international agreement halted most nonsubsistence hunting, but some native locals make a living from outfitting and guiding nonnative hunters who pay more than $25,000 to bag a polar bear. Derocher worries that in an increasingly fragile population, every breeding female of this slow-reproducing, long-lived mammal may become too important to lose to a bullet. Even tourism, while not a threat itself, presents increased opportunities for human-bear interactions that can place bears on the wrong end of a rifle.
ICE AND LIFE
The specter of ongoing climate change, however, trumps all these other threats. Polar bears are, in the parlance of wildlife biologists, "highly pagophilic," which means they are ice-loving and literally cannot live without it. The entire life cycle of the species is tied to seasonal changes in Arctic sea ice; bears routinely travel 3,000 miles a year, moving from ice floe to land to ice floe, completely comfortable on their frozen, floating homes. In one study, half of all polar bear maternity dens in Alaska were discovered on ice packs several hundred miles offshore.
Polar bears have a low reproductive rate. Females will not usually mate until they are five and generally have two cubs per litter, with a roughly 50 percent survival rate. They do not mate again until their cubs are grown (at about three years) and will not reproduce at all if conditions are unfavorable. The breeding season runs from March to May, but females may delay implantation of fertilized eggs until they are ready to den in late fall and conditions are right to bring their pregnancies to term.
Blind newborns weigh only about 1.5 pounds and spend their first several months in an ice den burrowed by their mother. During the long winter, the young bears nurse, growing to about 10 to 20 pounds by the time they emerge from the den in late March or early April. Then the cubs head out toward the sea ice to begin their rapid growth into the world's largest living land carnivore. (The biggest males can reach 1,800 pounds and stand up to 13 feet tall while on their hind legs.) Once the young leave the den with their mother, their lives become a sort of ice dance, moving farther offshore from May through August and back south in October. The relationship between ice and polar bear health and survival cannot be overstated.
The same can be said about the ringed and bearded seals that the carnivores feed on. Polar bears are as tied to the lives of these seals as lynx are to snowshoe hares and sea otters are to sea urchins--among the most singular predator-prey relationships in nature. Polar bears usually emerge ravenous from their long winter den in spring (they do not hibernate, per se, but expend little energy, lose weight and don't even defecate) looking to feast on newborn ringed seals. If ringed seals, which utilize snow caves to give birth and raise pups, lose a few weeks of their habitat because of earlier melting, their survival rates will likely drop. When unseasonable April rainstorms melted seal dens in recent years, for example, foxes and bears preyed more easily on the pups, raising the specter of seal population crashes. "Ice-dependent seals, walrus and polar bears--I don't know what they're going to do," says Craig George, a biologist with the North Slope Borough Department of Wildlife Management in Alaska.
After I left Kazlowski last October, the polar bears we had been observing dispersed when the near-shore sea ice froze solid. By early November, Kazlowski's guide, Jack Kayotuk, tracked one pregnant sow about 60 miles to where she established her den on a bluff overlooking the Beaufort Sea. He took a GPS coordinate and left the female to her long under-snow winter.
In early March, when darkness still enveloped the North Slope, Kazlowski awaited the cubs' appearance. Blowing snow had covered the den, but he observed a small hole with a cub's head sticking through. When a pair of young bears finally emerged, Kazlowski got a good look at them. "These little 10-pound balls of fluff" came out in 20-below weather, even at that tiny size, perfectly adapted to their environment. He watched the two cubs playing and sliding down a snow hill, nursing and roughhousing with their mom. Red foxes would come by, hoping to scavenge something, but kept a wary distance.
Watching the cubs with their mother, Kazlowski says, it was hard not to get a chill of fear that these young bears might not survive the dramatic and rapidly accelerating changes to their environment. "What are these cubs going to face in the next 20 to 30 years of their lives if things continue the way they're predicting?" he wonders.
A few days later, Kazlowski watched as a red fox came by and sat near the den hole, a sure sign that the polar bear mom and her cubs had made their way into the world, poised to face a profoundly different landscape--and a dubious future.
Colorado-based Daniel Glick is the author, most recently, of Monkey Dancing: A Father, Two Kids, and a Journey to the Ends of the Earth.
NWF Priority: Combating Global Warming
Global warming is posing a pronounced threat not only to polar bears and other Arctic animals but also to a wide range of species throughout the world. Combating this global danger is a top priority for NWF, which is backing bipartisan congressional legislation to reduce greenhouse gases, publishing reports on the effects of warming on wildlife and working with state affiliates on a variety of grassroots efforts involving climate issues. For more information, go to www.nwf.org/globalwarming.