The smaller the bird, for example, the more agile the flying — a swan may need the equivalent of two football fields to take off and get lift, while a hummingbird can rise like a helicopter.

例如，鸟类的体型越小，飞行动作就越灵敏——天鹅就需要两个足球场大的面积才能完成起飞和抬升动作，而蜂鸟就可以像直升机一样垂直起飞。