They must return to their roosting trees. 它们必须返回栖息地

124. Starlings.
     欧椋鸟
125. In the evening, they come back to the warmth of the city
     夜晚 它们在郊外摄食后
126. after feeding in the neighbouring countryside.
     返回温暖的城市
127. They must return to their roosting trees.
     它们必须返回栖息地
128. But the first to do so are at the highest risk
     但第一个回来的最有可能
129. of being caught by birds of prey.
     被猛禽袭击
130. So, they wait for others to arrive.
     所以它们等候大部队一同抵达

来自《行星地球 第二季 第六集 Planet Earth S02E06 城市》第 127 行