The study suggests that polar bears need more energy to survive than previously thought-and they might not be catching enough prey to meet those demands.
"The other bears either scavenged or they fasted, and they all lost mass", as much as 20 percent of their body mass, Mr. Pagano said.
Until now, there's been little information available on polar bears' daily energy demands and how they're affected by their day-to-day movements.
To measure the energy needs of wild polar bears, a team of biologists tracked free-ranging bears on sea ice near the northern coast of Alaska during spring, the animals' prime hunting season.
An adult male polar bear still-hunting at a seal hole on the sea ice of the southern Beaufort Sea
Using the Global Positioning System and video collars and the metabolic information, the researchers determined that the more a bear had to search for food the more energy it used.
'We found a feast and starvation lifestyle - if they missed out on seals it had a pretty dramatic effect on them, ' said a biologist who led the research. But later in the year, after the bears' long summer fast, those young seals are older and wiser, meaning polar bears are not able to catch as many. Last month, a video of a starving polar bear went viral, but it is from a different part of the Arctic and unlikely to be related to global warming, Durner said. He's been studying locomotion and metabolism in polar bears, including captive bears at the Oregon Zoo, for more than 10 years.
By comparing the bears' blood samples before and after, they could calculate the amount of carbon dioxide that the animal had produced, and thus its metabolic rate.
"The bears are moving with the ice and moving into these deeper water areas where it's thought they are having much less opportunity to catch seals". As the ice retreats farther and farther north, the bears may be forced to walk or even swim long distances just to reach a suitable hunting ground. The study shows If the bears don't eat that amount of food, they will lose weight quickly. As ice is now vanishing gradually, polar bears cant hunt seals.
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Catching enough to eat isn't the only challenge polar bears face. But some populations have seen sharp declines, while other researchers have found bears in some communities are smaller and less heavy than they used to be, he said.
The loss of sea ice has a domino effect on the species, which, in 2008, became the first animal listed under the Endangered Species Act due to threats from climate change.
The researchers monitored the bears' activity levels and metabolic rates while they hunted. "Unfortunately, with the rapid environmental changes occurring in Arctic sea ice, the specialization that once allowed polar bears to live in this challenging habitat has painted the animals into a physiological corner and led to devastating consequences", said wildlife eco-physiologist Terrie Williams, a study co-author who heads the university's Center for Marine Mammal Research and Conservation.
Until then experts had assumed that polar bears required less energy because they have no natural predators and their hunting method does not involve a lot of physical exertion: They sit on ice floes and wait for seals to emerge.
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Globally, the polar bear population is thought to be holding roughly steady at around 25,000-30,000, Andrew Derocher, who has studied the species Canada's University of Alberta since the 1980s, told Seeker.
However, it has been hard for scientists to analyze the behavior and fundamental biology of the bears in this harsh and remote environment, according to Pagano.
"Two-thirds of the world's polar bears could die out by 2050", cautions WWF, demanding an immediate decline in greenhouse gas emissions so the bears can stand a chance of survival.
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