Experts say the slow formation of winter ice on Hudson Bay this year has pushed some of Canada's polar bears to the brink of starvation and forced them to scrounge for food near old garbage dumps.

The bears weren't able to get onto the ice to hunt seals until late November this year, which observers say is becoming the norm.

David Barber, one of the world's top Arctic researchers, said Hudson Bay polar bears have lost six weeks of hunting time on the ice due to climate change.

The bay often doesn't freeze up until early December now and thaws earlier in the spring, he said, leaving polar bears with less time to bulk up on fatty seal meat.

'They're basically starving'

"Those bears are all lining up along the coast line waiting for the ice to form," said Barber, who holds the Canada research chair in Arctic science at the University of Manitoba.

"They're basically all starving. They are really at their limit biologically."

Polar bears depend on winter hunting to build up enough fat to carry them through the lean summer months on land. The bears lose at least one kilogram of fat a day when they aren't on the ice.

Given they are off the ice for up to 150 days, the hefty bears can lose well over 100 kilograms — leaving some emaciated by the time the ice freezes again.

Canada is home to about two-thirds of the world's polar bears but experts say climate change could make the Hudson Bay population extinct within a few decades.

"We don't expect the situation in Hudson Bay to go back to where it was in the '70s. We expect it to continue to deteriorate," Barber said.

"If the bears can't get back onto the ice until late November or early December now, 20 years from now it will be three weeks later than that. They're at their limit of their ability right now to fast for that length of [time]."

Starving bears spotted at garbage dumps

Peter Ewins, director of species conservation at World Wildlife Fund Canada, was at the Hudson Bay community of Churchill, Man., in November to observe the state of the bears first-hand.

As the temperature hovered around freezing, Ewins watched starving polar bears nosing around old grain stores and garbage dumps while others were found dead. The odd berry patch and goose egg nest isn't enough to sustain the massive mammal, he said.

"The weaker individuals, the ones who are less proficient at hunting, they were in poorer condition and it was visible this year," Ewins said. "It's just an indicator that those less fit, poorer quality bears were really up against the wall already."

With less time on the ice to gorge on seals, it's only a matter of time before starvation affects the fit bears as well, he suggested.

Daryll Hebman, regional wildlife manager with Manitoba Conservation, said he's been watching temperatures in the north closely and they haven't dipped below –40 C yet. He said that temperature is crucial to solidify ice and make it stable for hunting.

The lack of winter ice starts a vicious cycle, he explained. Bears can't get on the ice to hunt and, since the ice is not as thick, it doesn't last as long in the spring. Polar bears come off the ice thinner than they should be and can't last the five months until the ice forms again.

It's especially critical that female bears get as much ice time as possible, he added.

"If they're stressed going into that den and in less-than-perfect body condition, they may be walking out of that den with no cubs at all," Hebman said.

Trudy Wohlleben, senior ice forecaster with the Canadian Ice Service, said the freeze-up was about three weeks late in the fall. But ice conditions now on Hudson Bay seem to be close to normal with most of the water covered by a thin layer of first-year ice.

She said she doesn't know how long the ice will last since the service doesn't forecast beyond the next few weeks.