PLANET EARTH Ice Worlds

Crammed into this scrum, the birds are remarkably good natured, but they have to be. If the huddle breaks even for a moment, precious heat escapes. It's imperative（势在必行的） they reform as quickly as possible for only by as acting as one can the males withstand the elements, and protect their eggs. But their greatest test lies ahead. As winter advances, frequent blizzards drive the temperature down.



It's now 60 degrees below zero. The birds at the edge of the huddle bear the brunt（进攻） of the hundred mile an hour winds and so provide shelter to those taking their turn in the middle. Abandoned by the sun the males are left alone with their eggs to face the coldest darkest winter on Earth.



At the northern extreme of our planet the sun rises for the first time in months, illuminating a very different ice world. Unlike Antarctica, the Arctic is a vast frozen sea surrounded by land. Here winter is coming to an end but this bleak wilderness remains locked in ice. Eider ducks（艾德鸭） break the silence. They have stayed here braving the northern winter, instead of flying south to warmer climes.