S1, E4: Polar landscapes in autumn are transformed as the big freeze returns. Most animals leave on epic journeys, some now battle to breed, and for the hardy few it's a time of opportunity. In the Arctic, polar bears gather in large numbers on the coast to wait for the return of the ice. Tempers soon fray and violent contests break out. Off the coast 2,000 beluga whales head for a special estuary, a gigantic `whale spa'.