Fox Dives Head First in to Snow | Planet Earth II | BBC Earth

Sixty million tonnes of snow now blanket this herd's territory. Pushing through deep snow is exhausting work, and the bison are now slowly starving. Just keeping warm saps huge amounts of energy. Their thick coats can insulate them down to minus 20 Fahrenheit. It's now minus 40. The only thing that will keep them alive is buried beneath three feet of snow. And that's a problem shared with a surprising neighbour. The food the fox seeks is also deep beneath the snow. The survival of both creatures depends on getting through to the ground. For the bison, it will be a matter of brute strength. Massive neck muscles enable them to shovel five tonnes of snow a day. Their lightweight neighbour needs more precision. The bison have reached their goal. A mouthful of withered grass. And where the bison have dug, the fox now spots an opportunity. Every footstep counts, but he mustn't break through. Yet, he listens carefully to pinpoint his target. It's moving. A vole. Small, but a hundred times more nutritious than a mouthful of dried grass. To get through the winter on these prairies, sometimes brain beats brawn.