Wildlife biologist Ian Bullock is a seasoned visitor to the Arctic, but even he was surprised by what he saw last month: a thin female polar bear, shadowed by her cub, trying to challenge a much bigger, stronger male for food.

It wasn't much of a challenge, but it showed just how desperate she was, 

That desperation, he feels, stems from the fact that the Arctic's summer sea ice — which polar bears using as floating stations from which to hunt seals — has been shrinking over the last few decades due to a warming Arctic, forcing polar bears into smaller areas and more intense competition. 

"She was the thinnest female with cub I have ever seen," he said. "She had a single cub which implies she has already lost one other cub this year.

"If she cannot feed, she cannot suckle her cub; with a hungry cub it is even harder for her to hunt effectively, so from what I saw her last cub is at risk and ultimately so is she," he added. "This is why she was challenging a big male with food. She was hungry enough to take a big risk