Winter

Winter is the greatest test for life in the polar regions, as temperatures plummet to 70 below and winds reach 200kph. Only a few remarkable survivors gamble on remaining in these extreme conditions. In the Arctic, a female polar bear treks into the mountains to give birth. Out on the frozen ocean, the entire population of the world's spectacled eider ducks braves the winter in a giant ice hole. The forests are transformed by frost and snow and within, wolf and bison fight a desperate battle - and a remarkable alliance is made between raven and wolverine. More winter survivors hide beneath the snow, including tiny voles and their predators, the least weasel. In Antarctica, male emperor penguins face their darkest hour as they protect their eggs from fierce polar storms. Meanwhile, weddell seals escape to a hidden world of jewel-coloured corals and bizarre creates but ice stalactites reach down with deadly effect.