Melting sea ice forces polar bear to swim for nine days

In a remarkable feat of endurance, a polar bear has been tracked swimming for nine days continuously in a desperate bid to reach new ice floes, covering 426 miles in the process.

The bears are excellent swimmers and are known to travel long distances in search of seals. But scientists working for the US Geological Survey, who logged the animal's plight using a GPS tracking collar, said the animal's exertions were exceptional – and further evidence of the extent to which the melting of the bears' natural habitat due to global warming is threatening their very existence.

The research, published in the Polar Biology journal, found that swims of such extreme distances "may result in high energetic costs and compromise reproductive fitness".

The journey did not end happily for the tracked animal. As well as shedding 22 per cent of her body weight, she also lost her young cub.