英语听力：自然百科 大迁徙 Great Migrations—15（在线收听） |
Soon there may be violence as males joust to win female affections. But for now, everyone enjoys a touching reunion. The calf, out of his depth among these goliaths, returns to the mentoring eye of his mother. He may not leave her for another 10 years to join other young males in wandering bachelor groups. And he may be forty before he masters the global oceans on his own. It's September in North America. And over one billion monarchs have been winging their way south, racing to get to Mexico before the first frost. By soaring on wind currents, they save enormous amounts of energy and about half will survive the 2,000-mile journey. Their flashy coloration signals their toxic nature. But some predators can withstand the toxins like the praying mantis.
After more than two months, and up to 900 hours of flying, survivors begin to flutter into their wintering grounds in late October. Hundreds of millions of them now alight on this threatened patch of Mexican forest. They cluster in the same grove, sometimes even the same tree, as the great grandparents who started this strange odyssey. |
| 原文地址：http://www.tingroom.com/lesson/zrbaike/2010/259353.html |