the world's entire population in a single flock. 仅这一群便集中了世界上所有的花脸鸭

160. but most must make special preparations for winter and a life with little sun.
     而更多的却得专门为冬天做好准备 以度过缺少阳光的日子
161. Whole populations of animals are now forced to travel great distances in pursuit of food and warmth.
     动物们成群结队踏上 寻找食物和温暖的长途旅程
162. 300,000 Baikal teal gather to escape from the Siberian winter by migrating south to Korea -
     30万只花脸鸭集体迁往南方的韩国 躲避西伯利亚的严冬
163. the world's entire population in a single flock.
     仅这一群便集中了世界上所有的花脸鸭
164. But there are parts of the world that have no seasons.
     但是 世界上有些地方却没有四季
165. In the tropics the sun's rays strike the earth head on
     在热带地区 太阳辐射直射大地
166. and their strength is more or less constant all year round.
     全年始终或多或少地 受到这种影响力的控制

来自《行星地球 第一季 第一集 Planet Earth S01E01 从北极到南极》第 163 行