Polar bears are at greater risk of extinction than ever before as they are unlikely to adapt to longer Arctic summers, new research warns.
The more time the giant predator spends on land and away from sea ice, the greater the risk of starvation, scientists said.
Polar bears live in Arctic regions such as Canada, Alaska, Russia, Greenland and Norway.
Much of a polar bear’s time is spent on sea ice, where they hunt seals, rest, breed and care for their young.
Over three weeks of summer, twenty polar bears, closely observed by scientists, tried different ways to maintain their energy reserves, including resting, scavenging and foraging.
Still, almost all of them lost weight quickly: an average of about 2.2 pounds per day, according to the findings published in the journal Nature Communications.
Over three weeks of summer, twenty polar bears, closely observed by scientists, tried different ways to maintain their energy reserves – by resting, searching and foraging.
Some experts have speculated that polar bears might adapt to the longer ice-free seasons due to climate warming by behaving like their grizzly bear relatives and resting or eating terrestrial foods.
But the polar bears in the new study tried versions of both strategies, with little success. Study co-author Dr Charles Robbins, director of the Washington State University Bear Center, said: ‘No strategy will allow polar bears to persist on land beyond a certain time.
“Even the bears that were foraging lost their body weight at the same rate as the bears that were lying down.
‘Polar bears are not grizzly bears with white coats.
“They’re very, very different.” Adult male polar bears are usually larger than grizzly bears, but can grow up to 10 feet (3 meters) long and weigh 1,500 pounds (680 kilograms), compared to grizzly bears’ 700 pounds (363 kilograms).
To maintain their size, polar bears depend on the energy-rich fat of seals, which they catch best on the ice.
Little was known about polar bears’ energy consumption and behavior when confined to land, so researchers used collars equipped with video cameras and GPS to track them during the summer in Canada’s western Hudson Bay region.
Little was known about polar bears’ energy consumption and behavior when confined to land, so researchers used collars equipped with video cameras and GPS to track them during the summer in Canada’s western Hudson Bay region.
The team wanted to see what the specialist ice hunters ate and did during the extended periods of time on land, when their favorite seal prey was out of reach.
The researchers also weighed the bears before and after the observation period and measured their energy consumption.
Lead author of the study Dr. Anthony Pagano, a wildlife biologist researcher at the US Geological Survey Polar Bear Research Program, said: ‘We found a real diversity of bear behavior, and as a result we saw a wide range of energy expenditure.’
He said many of the adult male polar bears were simply laying to conserve energy, burning calories at a rate comparable to hibernation.
Others actively foraged for food, eating carcasses of birds and caribou, as well as berries, kelp and grasses.
Yet almost all of them lost weight quickly: an average of about one kilo per day
Overall, the researchers found a fivefold range in energy expenditure, from an adult man resting 98 percent of the time to the most active man running 205 miles.
Some adult females spent as much as 40 percent of their time foraging, but the researchers found that all that activity bore no fruit. Dr. Pagano said, “The terrestrial food provided them with some energetic benefits, but ultimately the bears had to expend more energy to access those resources.” Three polar bears went for a long swim – one swam 175 kilometers (about 110 miles) across the bay.
Two found carcasses in the water, a beluga and a seal, but neither bear was able to feed on their finds while swimming or bring them back to land.
Only one of the twenty bears gained weight after encountering a dead marine mammal on land.
The study focused on the southernmost part of polar bear range in western Hudson Bay, where climate warming is likely to hit the bears faster than other Arctic areas.
The area’s polar bear population has already declined by an estimated 30 percent since 1987.
The new study indicates that polar bears in the Arctic are at risk of starvation as the ice-free period continues to grow.
Dr. Pagano said: ‘As polar bears are forced onto land earlier, the period in which they normally acquire most of the energy they need to survive is shortened.’
He added: ‘With increased land use, the expectation is that we are likely to see an increase in famine, especially among adolescents and women with cubs.’