The disappearing polar bears
Hope, the sole polar bear at the St. Louis Zoo, is set to begin another summer of backstroking, ball-playing and other antics in the protective custody of the zoo’s Bear Bluffs exhibit.
Hope in St. Louis
Michael Abbene | St. Louis Zoo
Hope, the only remaining polar bear at the St. Louis Zoo, is 23 years old.
Meanwhile, far to the north, the 20,000 to 25,000 polar bears left in the Arctic wild will continue their precipitous population decline with another year of unusual starvation, drowning and infant mortality – a decline caused by melting sea ice.
Under court order, the Bush administration last week (May 14) reluctantly admitted as much by listing the polar bear as a “threatened” species under the Endangered Species Act. Technically, that means the bear is at risk of becoming “endangered” within the foreseeable future in all or much of its range. An endangered species is considered in immediate danger of extinction.
St. Louis scientists familiar with polar bears and climate change said the listing put into sharper focus the role of the huge white carnivore as global warming’s canary in the mineshaft and further illustrated how climate change induced by human use of oil, coal and other fossil fuels is putting life on the planet at risk.
The listing also was just the next step in an increasingly tragic saga of one of the greatest icons of the natural world, its possible extinction and the legal and political war over economic interests and health of the biosphere.
In recent years, scientists have found a rising number of starved and drowned polar bears, as well as evidence of cannibalism among bears. Some researchers believe a lack of food has cut into the already slow rate of polar bear reproduction. One federal study predicted the extinction of two-thirds of the global polar bear population and all 3,500 in Alaska by 2050.
In announcing the listing, Interior Secretary Dirk Kempthorne acknowledged that loss of sea ice is shrinking the habitat of polar bears, which were “likely to become endangered” within 45 years. But Kempthorne fell short of linking the polar bears’ demise to human-generated global warming.
St. Louis scientists familiar with the issue reflected the mainstream scientific view that the two were connected.
“As the climate changes, many habitats will be deeply affected, but none more than the Arctic,” said Peter Raven, president of the Missouri Botanical Garden and leader of several national and international studies of species extinction and climate change impacts.
“The world would be a poorer place, a diminished place, if there were no more polar bears,” Raven said. “It is well that we have resolved to save them and thus, necessarily, the starkly beautiful ice and snow fields that are their home. ”
Steve Bircher, curator of mammals at the St. Louis Zoo, said the listing was “inevitable.”
Biologists have known for years that polar bears were in trouble, Bircher said. A so-called flagship species, they were cited as vulnerable two years ago by the International Union for Conservation of Nature, the world’s oldest and largest network of conservation scientists, after a process that itself took many years.
“A polar bear is a barometer for what’s happening in their environment,” Bircher said. “Usually the flagship species is the one most sensitive to changes. When the bear is affected, it’s an indicator that something's not right.”
Polar bears live mainly in coastal areas of northern Alaska, Canada, Greenland, Norway and the former Soviet Union. Many migrate long distances to follow the seasonal expansion and contraction of the polar ice pack – their primary hunting grounds. They depend on access to large populations of seals and large expanses of sea ice.
“As the world climate inexorably warms, the many aspects of the habitat that the polar bear needs are shrinking,” Raven said. “Its hunting grounds are getting more and more limited, and the ice is often so slushy in winter that (the bear) can't get out to the places where it catches seals, or from one ice floe to another. ”
Commonly understood threats to wild polar bears include this destruction of their natural habitat, human development and poaching.
Too little genetic diversity
But the main threat now that bear numbers are so low is the loss of genetic diversity and thus, genetic health of the species. The estimated 20,000 to 25,000 bears may sound like a lot, but they are split into many separate groups.
“You have isolated pockets of individuals scattered across a large area,” the zoo’s Bircher explained. “That leads to inbreeding, increased susceptibility to disease and other problems. That’s why we’re so concerned.
“Critics who think, ‘What’s the matter, you still have thousands of bears?’ –- they don’t take these isolated pockets into account.”
Steve Bircher, curator of mammals at the St. Louis Zoo, urged people to visit Hope, who at 23 is near the end of the 20- to 25-year age range for a polar bear in captivity . She is one of about 80 polar bears at member institutions of North America’s Association of Zoos and Aquariums.
“Every year past 20 is a gift,” he said.
Visitors can “make a connection to what’s happening to these animals in the wild, to their environment. Then perhaps they can understand and come to the realization that there’s something we can do.”
That includes supporting political leaders who support steps to conserve the bears and their environment, Bircher said.
Said Peter Raven, president of the Missouri Botanical Garden: “The polar bear, like all other living beings, is a unique product of 3.5 billion years of evolution. Why do we assume that we have a right to end its existence on Earth, or to bring to extinction such a high proportion of what are, as far as we know, our only living companions in the universe?
“We have the power to slow down these changes, and we should do so.”
Kempthorne’s listing announcement came on the day of a court-ordered deadline forcing the Bush administration to follow federal law. Conservation groups sued in December 2005 to get the administration to consider listing the bear. A series of court actions followed.
“This decision is a watershed event because it has forced the Bush administration to acknowledge global warming's brutal impacts,” said Kassie Siegel, an official with one of the groups, the Tucson-based Center for Biological Diversity.
Kempthorne showed maps to illustrate the dramatic melting of sea ice, which last year contracted to a record low.
But he also took the unusual step of ruling that he would not allow the use of the Endangered Species Act to protect the bear by regulating U.S. contributions to global warming.
The polar bear listing “should not open the door to use of the ESA to regulate greenhouse gas emissions from automobiles, power plants, and other sources,” Kempthorne said.
Although they praised the Bush administration for the listing, the conservation groups ridiculed Kempthorne’s ruling, which Siegel said was “illegal and won’t hold up in court.”
"It's not too late to save the polar bear, and we'll keep fighting to ensure that the polar bear gets the help it needs through the full protections of the Endangered Species Act,” she said.
William Allen teaches science journalism at the University of Missouri at Columbia. He reported on science, medicine and the environment for the St. Louis Post-Dispatch from 1989-2002.