and fill the branches of their favourite trees. 挑选最喜欢的树枝落脚

134. How, or indeed why, they perform these marvellous aerobatics,
     它们是如何 又是为何成群起舞
135. we still do not fully understand.
     至今我们还无法完全理解
136. Eventually, en masse, they brave the descent
     最终 它们会成群结队地降落
137. and fill the branches of their favourite trees.
     挑选最喜欢的树枝落脚
138. On these cold winter nights, the city's extra warmth
     在这样寒冷的冬夜里
139. can mean the difference between life and death.
     城市的温暖可能事关生死存亡
140. A city, of course, can provide
     城市不仅能提供大量食物与庇护所

来自《行星地球 第二季 第六集 Planet Earth S02E06 城市》第 137 行