Polar bears failing to adapt to global warming

Polar bears are unable to adapt their behaviour to cope with the food losses associated with warmer summers in the Arctic, the BBC reports.

Scientists had believed that the animals would enter a type of 'walking hibernation' when deprived of prey, however new research suggests that bears starve when hotter conditions prevail and food becomes scarce.

The authors of the paper, published in the scientific journal Science, say that the implications for the survival of the species in a warmer world are grim.

The study required some 200 people, as well as the hiring of an icebreaker and helicopters, and researchers believe that the endeavour is unlikely ever to be repeated,

Back in 2008 polar bears were listed as a threatened species, and at that time, the Secretary of the Interior noted that the dramatic decline in sea ice was the greatest threat the bears faced. Research shows that polar bears survive on a diet of seals that they hunt on the sea ice. However,  increased melting in the summer reduces seal numbers, and as a result the bears struggle to find a meal.

Some researchers have argued that polar bears would deal with a reduced calorie intake by entering a low-activity state termed 'walking hibernation', similar to the way that many species of bear cope with winter.

Scientists embarked on a dangerous and expensive trial to test this idea. The test consisted of attaching satellite collars and surgically implanting logging devices to track the bears' movements and record physiological details.

The study reportedly involved more than two dozen bears in the Beaufort Sea, north of Alaska, and it concluded that in the summer seasons, the bears didn't slow down, but simply starved when food was short.

"Their metabolism is very much like a typical food limited mammal rather than a hibernating bear," said John Whiteman from the University of Wyoming, the paper's lead author.

He added however, that while the bears may not be able to change their behaviour when it comes to food, they do seem to have a significant adaption that helps them to cope with swimming in cold water.

"They have this ability to temporarily allow the outermost portion of the core of the body to cool off substantially and this protects the innermost vital organs - there was not an expectation of that, it was very surprising," said Whiteman.

The researchers detailed the extraordinary swimming ability of the bears in their study, with one female surviving a nine day, 400 mile swim from shore to ice. When she was re-captured some seven weeks later, the bear had lost 22% of her body mass, as well as her cub, the researchers added.

"We've uncovered what seems to be a fascinating adaptation for swimming in cold arctic waters, but I don't think that is going to play as big a role in determining their fate as the loss of hunting opportunities will," said Whiteman.

"We think this data also points towards their eventual decline," he added.