PLANET EARTH Ice Worlds
The calves are born well before the spring melt giving them a head start when summer finally arrives. It must get to grips with its new ice world benign one minute life threatening the next. Even in spring winds chill to the bone（寒风刺骨）. The calf must stay close to its mother to avoid getting lost in the sudden blizzard.
Arctic wolves. In the whiteout, the threat is almost impossible to detect but the musk oxen instinctively retreat to higher ground. Forming a defensive ring around their calves the adults present a barricade that few hunters could breach but the wolves need not risk injury today. A calf has been left behind in the panic.
With each passing day the sun climbs higher in the sky and it's rays strike the Arctic more directly. It's spring and new life stirs. The polar bear cubs emerge from the den in which they were born. Their mother stretches her legs after five months under the snow. They're just two months old and instinctively follow her lead. A steep slope makes the best site for a den but it's a tricky place to take your first steps. It may look like fun, but this is serious training for the task ahead. There's no food on the slopes and the family will need to head out across the frozen sea, before the mother's milk runs dry.
