When the team recaptured the bears 8 to 11 days later, changes in the ratio of isotopes in their blood gave a measure of metabolic rate. "This study identifies the mechanisms that are driving those declines by looking at the actual energy needs of polar bears and how often they're able to catch seals".
Best estimates say there are 20,000 to 30,000 polar bears in 19 different groups or populations scattered across the top of the U.S., Canada, Greenland, Norway, and Russian Federation.
The GPS told them the distances the bears wandered, and the video camera recorded if the bears were successful in killing and eating prey.
According to recent measurements, the extent of Arctic sea ice is decreasing at a rate of about 14 percent in every 10 years, which can significantly reduce polar bears' access to seals.
The bear videos showed researchers all sorts of usually private aspects of polar bear life, including courtship and hunting. And every additional mile that a polar bear has to traverse under its own power is that much more food the bear has to eat.
But the scientists found the bear's metabolic rate was 1.6 times greater than previously thought - akin to that of other carnivores. Because of the video footage, the researchers know that these bears gained weight because they caught seals.
While four bears put on weight, five bears lost up to 10 per cent of their body weight - between 18 and 20 kg - in 10 days.
But Canada must do more to improve its oil spill response capabilities and to protect polar bear habitat.
Retreating ice sheets, a result of climate change, are forcing the bears to travel greater distances to find the food they need. That helps the bear to gather a lot of fats and help them to survive more a long time without any foods. To minimize their energy consumption the bears still-hunt, waiting for hours by seals' cone-shaped breathing holes in the sea ice.
Mr Pagano and his collaborators monitored the behaviour, hunting success and metabolic rates of bears as they hunted on the sea ice in the spring. Polar bears rely on seals for their vast caloric needs-the four bears that lost 10% of their weight didn't catch a single seal during the study and relied on scavenging-and sea ice is pretty much a requirement for polar bears to catch seals. Less sea ice means the bears have to work harder to find them. In the Beaufort Sea, sea ice starts to retreat away from the continental shelf in July, and most of the bears move north on the ice as it retreats. It has been hard, however, for researchers to study the fundamental biology and behavior of polar bears in this very remote and harsh environment, Pagano said.
Photographs of super-skinny polar bears with ribs poking through snowy-white coats have become a doomsday image of the problems faced by these highly specialised creatures - now down to as few as 22,000 individuals - because of climate change.
Polar bears are starving during their prime hunting period as Arctic ice melts because of climate change, according to a United States study published Thursday that analysed the animals' metabolism for the first time.
Previous studies had tried to estimate polar bear metabolic rates and energy expenditures based on some assumptions about their behavior and physiology.