Polar bears are at greater risk of extinction than ever before as they are unlikely to adapt to longer Arctic summers, warns new research.
The more time the giant predator spend stranded on land and away from sea ice means a greater risk of starvation, said scientists.
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.
During three summer weeks, 20 polar bears closely observed by scientists tried different ways to maintain energy reserves – including resting, scavenging and foraging.
Yet nearly all of them lost weight rapidly: on average around 2.2 pounds per day, according to the findings published in journal Nature Communications.
During three summer weeks, 20 polar bears closely observed by scientists tried different ways to maintain energy reserves – including resting, scavenging and foraging
Some experts have speculated that polar bears might adapt to the longer ice-free seasons due to climate warming by acting like their grizzly bear relatives and either rest or eat terrestrial food.
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 Centre, said: ‘Neither strategy will allow polar bears to exist on land beyond a certain amount of time.
‘Even those bears that were foraging lost body weight at the same rate as those that laid down.
‘Polar bears are not grizzly bears wearing white coats.
‘They’re very, very different.’ Usually larger than grizzly bears, adult male polar bears can reach 10 feet in length and weigh 1,500 lbs (680 kilos) compared to grizzly bears’ eight feet and 800 lbs (363 kilos).
To maintain their bulk, polar bears rely on the energy-rich fat of seals, which they best catch on the ice.
Little was known about polar bear energy expenditure and behavior when confined to land, so researchers used collars fitted with video cameras and GPS to track them summering in the western Hudson Bay region of Manitoba in Canada
Little was known about polar bear energy expenditure and behavior when confined to land, so researchers used collars fitted with video cameras and GPS to track them summering in the western Hudson Bay region of Manitoba in Canada.
The team wanted to see what the specialized ice-hunters ate and did during the extended time on land when their preferred seal prey was out of reach.
The researchers also weighed the bears before and after the observation period and measured their energy expenditures.
Study lead author Dr Anthony Pagano, research wildlife biologist with the US Geological Survey Polar Bear Research Program, said: ‘We found a real diversity of bear behaviors, and as a result, we saw a diverse range of energy expenditures.’
He said many of the adult male polar bears simply laid down to conserve energy, burning calories at rates similar to hibernation.
Others, actively searched for food, consuming bird and caribou carcasses as well as berries, kelp and grasses.
Yet nearly all of them lost weight rapidly: on average around one kilo (2.2 pounds) per day
Overall, the researchers found a five-fold range in energy expenditure from an adult male that rested 98 percent of the time to the most active who clocked 205 miles (330 kilometers).
Some adult females spent as much as 40 percent of their time foraging, but the researchers found that all that activity didn’t pay off. Dr Pagano said: ‘The terrestrial foods did give them some energetic benefit, but ultimately, the bears had to spend more energy to access those resources.’ Three polar bears went for long swims – one swimming 175 kilometers (about 110 miles) across the bay.
Two found carcasses in the water, a beluga and a seal, but neither bear could feed on their finds while swimming nor bring them back to land.
Only one bear out of the 20 gained weight after stumbling across a dead marine mammal on land.
The study focused on the southern-most extent of polar bear range in the western Hudson Bay, where climate warming is likely impacting the bears at a faster rate than other Arctic regions.
The polar bear population in the area has already declined by an estimated 30 percent since 1987.
The new study indicates that polar bears across the Arctic are at risk of starvation as the ice-free period continues to grow.
Dr Pagano said: ‘As polar bears are forced on land earlier, it cuts into the period that they normally acquire the majority of the energy they need to survive.’
He added: ‘With increased land use, the expectation is that we’ll likely see increases in starvation, particularly with adolescents and females with cubs.’