For Emporia physician Jack Havenhill, the good news is that polar bears finally may be put on the threatened species list. The bad news is that public hearings will delay a government decision for about a year.
Then a plan will need to be devised and implemented to slow global warming and save the bears’ habitat, which Interior Secretary Dirk Kempthorne says “may literally be melting.”
Whether they’re grizzlies, black bears, Alaska Coastal bears, polar bears or others, Havenhill has a well-rounded knowledge of all of them. To study them, he and his wife, Ann, have visited a host of wilderness areas that are home to all sorts of bears.
He chartered a float plane, landed on the water off Kodiak, Alaska, and waded in for a close look at Alaskan Coastal bears. Later, the Havenhills went to Churchill, Manitoba, Canada, for an up-close look at the largest single cohort (herd) of polar bears known.
Polar bears, which evolved from the Alaskan Coastal bears, a variety of grizzly, began moving onto the ice about 100,000 years ago.
“They’re really ‘Ursa maritimus,’ which means ‘sea bear,’” Havenhill said, “so a better name for them would be ice bear. Their livelihood is completely tied up with sea ice.”
They leave the ice only to den and to sleep.
That is where global warming and a threatened species enter the picture. Worldwide, he said, there are about 25,000 polar bears that live in about 20 different groups. About 15,000 of those live in Canada, which has more polar bears than any other country. The Churchill cohort consists of fewer than 1,000 bears, which den and sleep south and east of Churchill, near the Hudson Bay. A decade ago, the polar bear population was around 1,200 at Churchill.
As average annual temperatures continue warming, Hudson Bay’s ice melts earlier and cuts off the polar bears from the ice and the fatty food they need to survive during the time they are marooned on land.
Havenhill said that one climatologic model predicts the Arctic will be ice-free in the summer by 2100; another mentions the year 2040. Either way, the lack of sufficient ice and food could drive polar bears to the brink of extinction.
Even though they are carnivores, they rarely eat fish, Havenhill said, and because running polar bears use about double the energy of other animals, they cannot hunt moose and other potential prey. Instead, they hunt on the ice by lying near ring seals’ breathing holes and snagging the seal pups as they come up for air. Polar bears often eat only the plentiful fat layers of the seals, which provides higher caloric value and thus more stored fat for their trip to shore.
“They are tied to the ice. They have one major and almost exclusive food, and that is ringed seal,” he said. “So, as the ice decreases, the habitat of the polar bear decreases and it may well be that its food supply, the ringed seal, will also be reduced.”
Perhaps the greatest problem is the effect the early ice melts have had on the polar bear’s reproduction process.
Females’ pregnancies rely on weight gains to be successful. They breed in April and May, when the female weighs 400 to 450 pounds.
“She has to gain at least 200 pounds between the time she mates and the time the ice breaks up in July,” Havenhill said. Pregnancy for a 660-pound polar bear is a “marginal proposition.” Ideally, she should weigh closer to 800 to 900 pounds.
Early ice melts have shortened the feeding period about three weeks, making it difficult for the female to make the essential weight gain to support a pregnancy. Unlike most animals, there is a lapse of months between egg fertilization and the time the fetus implants itself securely in the female to develop.
“Implantation and pregnancy do not happen until September,” Havenhill said. When the other bears leave Churchill, after the ice reforms in late October and early November, the pregnant females stay in the den and sleep, not returning to the ice until sometime in March.
Unlike other bears, the polar bear does not hibernate, she merely sleeps. While a hibernating bear is next-to impossible to rouse from hibernation, polar bears can be wakened easily and are ready to defend themselves. In the den, the polar bear’s heartbeat slows from about 70 beats per minute to 10-12 bpm. The body temperature, however, drops only about 10 degrees, to 90 degrees Fahrenheit, instead of the 40 degrees common with other bears.
“They have to have a high enough metabolic rate to handle the pregnancy and to nurse the cubs,” Havenhill said. Higher metabolic rates and warmer body temperatures associated with sleeping consumes calories much faster than does hibernating. That, combined with an inadequate feeding period, creates trouble.
“Insufficient weight gain impairs fertility and litter size is reduced,” Havenhill said. “It used to be that twin cubs were the most common litter size. Now they’re not.”
Most females give birth now to only one cub, and the cub survival rate has dropped because the underweight mothers simply don’t have the energy to take care of them, he said.
The threat to maintaining healthy populations of polar bears is exacerbated by the reproduction cycle of the bears themselves.
“Female polar bears sexually mature at five,” Havenhill said. Cubs stay with their mothers for about two and a half years.
“So she’s only going to have a litter every three years.”
With a 20-year expected life span and three years between each pregnancy, the bears have about four opportunities to reproduce and even then, they are producing about half the number of cubs they did in years past.
Havenhill worries that before too many years pass, zoos may be the only place that humans can get a look at a live polar bear.
That was one of the reasons the Havenhills wanted to go to Churchill to see them in the wild. They flew over the area to sight the bears and toured in a Tundra Buggy, a high-tracked, multi-windowed vehicle that is sturdy enough to withstand face-to-face encounters with the aggressive polar bears. Passengers are forbidden to get off the buggy, for their own safety, until it returns to town.
One of the Churchill bears had killed a student in 1968, and since that time, residents and naturalists have worked together to find a way to co-exist peacefully with the bears.
The city adjusts its activities to accommodate the presence of the bears. Humans do not go outside after sunset because that often is when the bears come to town. The exception is on Halloween night, when helicopters fly around the city limits to frighten the bears away and allow children to trick-or-treat safely.
The city has built a “polar bear jail,” Havenhill said, to house bears who’ve become too aggressive in town. They are drugged and hauled to the jail and later taken out and set free in the wild, miles away. Repeat offenders who come to the jail for the third time have to be destroyed, for the safety of the community.
To the extent possible, however, some humans already are working to maintain the polar bear population as long as possible.
Hunting already has been prohibited, except in limited numbers taken by natives, and it is illegal to trade in polar bear skins. Others are trying to find ways to stop what appears to be a steadily changing climate.
“What people don’t realize,” Havenhill said, “is that just as global warming will affect the polar bear, it will affect all of us.”