By international zoo standards, this enclosure is not bad. Some polar bears are displayed on small concrete shelves above tiny pools, says Victor Watkins, the wildlife director of the World Society for the Protection of Animals. "The facilities in Japan are particularly appalling, some as small as 20 square metres." The Edinburgh Zoo enclosure is built of stone, about 40 metres in diameter with rocks and logs and the L-shaped moat. The pen lacks only three things: ice, seals and space. Especially space.
In the wild, Mercedes would be travelling thousands of kilometres across the Arctic pack ice in search of the holes where seals emerge to breathe. She might have to wait patiently for hours, but then, with one swipe of a giant forepaw, would claim a meal. By autumn, this diet would have built up a layer of fat 12cm thick, enough to keep her sustained all winter. The prospect for polar bears is of global warming reducing the extent of the ice. And, possibly doomed as feral creatures, they can hope for little by way of quality of life in zoos. In captivity, large animals, especially carnivores, often demonstrate "stereotypical behaviour" - repetitive movements such as pacing in a figure eight or bouncing up and down. Zoologists believe it's a way of coping with the stress of imprisonment. Polar bears suffer from this more than any other species. A zoo in Canada had to put one on Prozac.
An estimated 1,000 polar bears live in captivity around the world. Most reputable zoos have been reconsidering the ethics of keeping them, but polar bears, like elephants and big cats, attract lots of young visitors. In Calgary, Alberta, the zoo promised never to bring in another polar bear. Under new management, it has now reversed that policy, sparking public opposition led by a group called Zoo Check. The same thing is now happening at Edinburgh, which said in 2003 that after Mercedes died it would not bring in any more. Now it has changed its mind. "Keeping polar bears in captivity is completely unjustifiable," says Ross Minett, the director of Advocates for Animals, which is leading the fight against replacing Mercedes. "Your average polar bear enclosure in a zoo is one millionth of the area of a home range in the wild," he says.
This is my first visit to Edinburgh Zoo, but it's possible that I've seen Mercedes before. She was a three-year-old adolescent when she was captured in Churchill, Manitoba, 22 years ago. I had worked for a freight company there between university terms two years earlier, and had often gone to the town dump to see the polar bears foraging as they waited for Hudson Bay to freeze over. Mercedes could easily have been one of the cubs I saw learning how to survive from their mothers. I'd love to learn more about Mercedes, but the zoo isn't talking. "We've had a lot of bad press," explains a spokeswoman. What I do know is that Mercedes is 25 and was named after the German motor company that paid to ship her from Canada. Her mate, Barney, suffocated in 1996 when he swallowed a child's plastic toy in the moat. The pair had two cubs, both now dead. One of them, Minty, was the mascot for Fox's Glacier Mints.
A sign on Mercedes's enclosure says she was rescued from almost certain death after being caught three times in Churchill. This would have been no idle threat. No one walks around unarmed in Churchill. Polar bears are the top of the food chain, and an adult male can weigh as much as six brawny men. When humans and polar bears meet in the wild, it frequently results in death, usually the bear's. Those that are spotted in town, if they're not an immediate threat, are sedated with a dart gun and carted off to the polar bear jail where they cool their paws until the bay freezes over.
Persistent offenders are tagged as "nuisance" bears and can be culled by wildlife authorities. The Arctic explorer Sir Ranulph Fiennes is a polar bear fan, calling them "magnificent" and "beautiful", yet even he has been forced to shoot at a bear in self- defence. Near the end of his three-year circumnavigation of the globe via the poles, he spent three months drifting on an ice floe. "We had 19 separate bear visits," he recalls. "Most of them we scared away by banging cooking pots, but one didn't respond. It had one thing in mind. I had a .44 Ruger and fired over its head and through its legs but to no effect. Finally, when it was 15 metres away, I aimed for its death point, in the chest. I missed and hit its foot. Fortunately it made a noise and lurched off backwards. If we had killed it we'd never have been able to shift a two-ton animal to the edge of the floe."
Ursus maritimus is a young species. Polar bears evolved from grizzly bears between 200,000 and half a million years ago, long after early hominids emerged. Yet in that time they have adapted perfectly to their extreme environment. Their large paws, up to 30cm in diameter, are partly webbed, and work like paddles in the water and snowshoes on land. At sea, they have been tracked for 100km, but they could easily swim much further. On land, their paws have a non-slip surface, one claw permanently extended to dig into the ice.
Although their double layer of fur is white, the skin below is the same pitch black as their snouts. A popular myth is that the outer guard hairs act like fibre-optic cables, carrying sunlight past the thicker, inner fur to be absorbed by the skin. It's not true, and scientists say that even if it were, the bears would not get enough heat from it to make much difference. Polar bears have a keen sense of smell and can detect a seal from 32km. But seals aren't stupid, and hunting them requires tactics. When stalking prey on the ice surface, some bears put their paws over their black noses to make themselves less conspicuous, says Rob Laidlaw, a biologist with Zoo Check in Canada. Others will push a pile of snow slowly in front of them, like Birnam Wood sneaking up on Dunsinane.
But for all their strength, specialisation and wiles, polar bears are in trouble as their habitat deteriorates. Professor Julian Dowdeswell, the director of the Scott Polar Research Institute at Cambridge, says that since satellite observation began 30 years ago, the sea ice has retreated by 5 to 15 per cent. In Churchill, that has extended the ice-free summer by three weeks. And every week cuts the amount of fat a bear will have accumulated by the onset of winter by 10kg to 20kg. As females don't eat for the eight months of their pregnancies, relying entirely on stored fat, this trend could have a catastrophic effect on the species' reproduction.
"You're not going to have sea ice in summer in the Arctic well before the end of the century, and some time around then you're not going to have polar bears," says Samantha Smith, the director of the WWF arctic programme in Oslo, Norway. And within 45 years, three polar bear generations, their numbers are expected to fall by 30 per cent from their current level of 21,000-25,000 bears. On the western side of Hudson Bay, their most southerly range, numbers have already started to decline, falling from 1,200 in 1987 to 950 in 2004. The threat is so great that polar bears were added to the Red List of endangered species for the first time last month.
Sir Ranulph argues that the only solution is for zoos to take on the task of species preservation. "If they don't exist any more because the territory is no longer under ice, the decision is clear. By that time we must have a supply of polar bears in zoos."
The Arabian oryx, a type of antelope, was reintroduced to Oman from zoos in 1982, a decade after hunters drove it to extinction in the wild, he notes. Polar bear preservation enclosures would have to be much larger than anything that exists today, Sir Ranulph says. And the captive population would have to be big enough to avoid inbreeding.
At the opposite pole, Ross Minett of Advocates for Animals is appalled by the preservation proposal. No polar bears have ever been reintroduced to the wild; they wouldn't have the skills to survive and would be too familiar with humans. "I'd rather they go extinct than be kept in captivity," he says. "What is the point of preserving a species if there's nowhere for them to go except to be driven to madness?"
LIFE CYCLE OF A POLAR BEAR
Females are ready to mate at four to six years, males a little later. The season is between April and May, and a week or so after mating, the normally solitary animals go their separate ways
After gestation of 39 weeks, polar bear cubs, usually two but up to four, are born between November and January. At birth they are 30-35cm long, blind, toothless and weigh little more than 500g
By April, the cubs are fully furred and emerge from the den. They stay with their mother until the age of two. Then they leave, and she starts the breeding cycle again
A full-grown bear can be more than 3m long,
and is the world's largest carnivorous land animal. It lives only in the Arctic, with around 60 per cent of the total population in Canada
They normally live 15 to 18 years in the wild, until the challenge of finding food (they have been known to walk 80km a day) becomes too much. In captivity, they can survive until their late thirties