It is a surprise because these shelves are frequently faced with cliffs that may be tens of metres high in places. But somehow, the emperors find a way up to breed, and also to come and go as they forage for the seafood that will sustain their chicks. "We thought that in years when the sea ice was bad, they just didn't breed, but they're clearly more adaptable than that," said lead author Peter Fretwell from the British Antarctic Survey.