But the skuas have not chanced upon the petrels, they've been waiting for them. 但是贼鸥碰到海燕并非机遇使然, 它们早就等着下手

44. First, though, valuable nesting places must be defended from property thieves.
    不过先得保护好来之不易的筑巢地 免得被其他鸟类占据
45. After laying their eggs, the petrels take time out to clean their plumage.
    产蛋后雪海燕会在抽出时间在雪地里整理羽毛
46. The south polar skua is a formidable opportunist.
    南极贼鸥是可怕的机会主义者
47. But the skuas have not chanced upon the petrels, they've been waiting for them.
    但是贼鸥碰到海燕并非机遇使然, 它们早就等着下手
48. These birds do not need to go to the ocean for their food.
    贼鸥不需要到海洋里捕食
49. The skuas can survive further south than any other predator
    与其他猛禽相比 贼鸥的厉害在于它能在地球的最南端生存
50. by exploiting the petrels' desperate need for bare rock.
    它们知道利用海燕必定寻找裸岩筑巢的弱点

来自《行星地球 第一季 第六集 Planet Earth S01E06 冰雪世界》第 47 行