Mongolian gazelle. 蒙古瞪羚

15. In the distant reaches of outer Mongolia,
    在遥远的外蒙古大草原
16. one of the planet's great migrations is underway.
    地球上规模最大的迁徙大军正浩浩荡荡地行进着
17. Few people ever see this extraordinary annual event.
    这一蔚为壮观的场面一年一次 但却很少有人亲眼目睹
18. Mongolian gazelle.
    蒙古瞪羚
19. Two million are thought to live here, but no one really knows.
    共约两百万只瞪羚生活在此处 但具体数量仍不得知
20. For much of the time, they're scattered through this vast landscape,
    瞪羚在大部分时间里 都各自流浪在这片广袤的大地上
21. but once a year they come together to have their young.
    然而 每年总有一次 这些它们将会聚集在一起 繁衍后代

来自《行星地球 第一季 第七集 Planet Earth S01E07 伟大草原》第 18 行