Back in Antarctica,the emperor penguins' trek to their breeding grounds is well underway.
It's a long slog and the frozen sea ice presents all kinds of challenges.
But the occasional slip-up is the least of their worries.
A small crack has appeared.
It's enough to stop the whole march in its tracks.
Cracks form as the sea beneath the ice rises and falls.
He's nervous,but the march must go on.
The rest try their luck with varying degrees of success.
They have reason to be frightened-leopard seals patrol these tide-cracks,looking for struggling penguins.
As more pile in,they pulverise the ice,making it even harder to escape.
But they possess a useful tool-an ice pick that gets them out of trouble.
