A polar bear stirs.

She has been in her den the whole winter.

Her emergence marks the beginning of spring.

After months of confinement underground, she toboggans down the slope, perhaps to clean her fur, perhaps for sheer joy.

Her cubs gaze out of their bright new world for the very first time.

The female calls them, but this steep slope is not the easiest place to take your first steps.

But, they are hungry and eager to reach their mother, whose delayed feeding them on this special day.

Now she lures them with the promise of milk, the only food the cubs have known since they were born deaf and blind beneath the snow some two months ago.

Their mother has not eaten for five months and has lost half her body weight.

Now she converts the last of her fat reserves into milk for her cubs.

The spring sun brings warmth, but also a problem for the mother.

It starts to melt the sea ice.

That is where she hunts for the seals she needs to feed her cubs, and she must get there before the ice breaks up.

For now, though, it's still minus 30 degrees, and the cubs must have the shelter of the den.