Polar bears normally feed on ringed seals that they catch on ice floes(浮冰) offshore. But as the ice disappears in a warming world, many bears are spending greater amounts of time on shore, eating birds' eggs, berries and grass. However the animals rapidly lose weight on land, increasing the risk of death. The polar bear has become the victims for global climate change, but the reality of the impact on this species is complicated.
Increasing global temperatures are now seen as their biggest threat. That's because the frozen Arctic seas are key to their survival. The animals use the sea ice as a platform to hunt ringed seals, mostly in late spring and early summer. But during the warmer months many parts of the Arctic are now increasingly ice-free.
To understand how the animals survive as the ice disappears, researchers carried out a study, where they followed the activities of 20 polar bears during the summer months over a three-year period. As well as taking blood samples, and weighing the bears, the animals were fitted with GPS-equipped video camera collars. This allowed the scientists to record the animals' movements, their activities and what they ate.
In the ice-free summer months, the bears adopted different strategies to survive, with some essentially resting and conserving their energy. The majority tried to search for vegetation or berries or swam to see if they could find food. Both approaches failed, with 19 of the 20 bears in the study losing body mass, by up to 11% in some cases. On average they lost one kilogramme per day. "Regardless of which strategy they were trying to use, there was no real benefit to either approach as far as being able to prolong the period that they could survive on land," according to lead author Dr Anthony Pagano, from the US Geological Survey in Alaska.
"It is likely that polar bears will disappear from areas where sea ice will be lost in future, but difficult to say just when and where," said Jon Aars from the Norwegian Polar Institute who was not involved in the study.
