英语听力：从南极到北极 4

Day 10. And the mother has let her cubs a mile from the den. It’s time to put them to the test. They’ve grown enormously in confidence, but they don’t have their mother’s sense of urgency. At last it seems that they are ready for their journey. And they are only just in time, for a few miles in the coast the ice is already splitting. Now the mother can start hunting for the seals they must have. But she is leading her cubs into a dangerous new world. Nearly half of all cubs die in their first year out on the ice.

Summer brings 24 hours of sunlight and a thawing, shifting landscape. Futher south, the winter snows have almost cleared from the Arctic tundra. Northern Canada’s wild frontier. Here, nature stages one of her greatest dramas.

Every year, three million caribou migrate across the Arctic tundra. The immensity of theherd can only be properly appreciated from the air. Some herds travel over two thousand miles a year in search of fresh pastures. This is the longest overland migration made by any animal.