they're worth tolerating because they provide a valuable early warning system. 它们还是值得忍受的 它们可以在危险来临之前给鼠兔预先的警告
they are liable to feed and drink for just a few hours 饮水的饮水 吃草的吃草 个个毫无留恋之情
They come and go as they please and much of their behaviour seems unfathomable to an outsider. 随兴而来随兴而去 对于外人来说 这些雌驴的脾性好像是不可捉摸的
they can cover nearly 2,000 miles during the summer months. 差不多整个夏季能够行进2000英里
The wolves will starve if they don't find the caribou. 狼若找不到驯鹿 就会饿死
As soon as couples arrive, they must stake a claim to a nesting patch. 一对雪雁来了之后就必须取得自己的筑巢地
Exhausted and starving, they touch down inside the Arctic Circle, 虽然早己精疲力竭 饥肠辘辘 但它们终于返回了北极圈
They winter along the Gulf of Mexico, and in spring they fly the entire length of North America to reach the Arctic tundra. 它们在墨西哥湾越冬 等到春天便一路飞过北美洲 来到这里的北极苔原
They trim the grass down to its roots, leaving little in their wake, 这些角马拼命地吃草 把草根上面的草茎部分全部吃掉