时差N小时 自然界的直升机（在线收听）

Most birds flap their wings up and down, but hummingbirds move their wings in a figure-eight pattern.

大多数的鸟是上下拍打翅膀飞行，但蜂鸟不一样，它是以八字形移动翅膀。

With each flap they twist their wings one-hundred-eighty degrees so that they create a downwardthrust on both the forward and backward strokes.

蜂鸟每次拍打翅膀都会旋转180度，以便为前后的拍打创造一个推力。

If each loop of the wings is of the same strength, they hover.

如果每次翅膀旋转的力度一样，蜂鸟就会盘旋在空中。

They can go forward, backwards, orsideways by tilting their wings in the direction they want to go.

它们只要往想去的方向倾斜翅膀，就可以前进，后退，或横向移动。

Kind of like a helicopter.Exactly.

就像直升机一样。是的。

In order to hover, hummingbirds have to be really strong.

要盘旋在空中，蜂鸟必须得很强壮。

Their wing muscles are thirty percent oftheir total weight.

它们翅膀的肌肉重量占身体整个体重的三分之一。

When a small hummingbird hovers it flaps its wings about eighty times persecond.

一只小蜂鸟盘旋在空中时，翅膀的震动频率约为每秒80次。

Hummingbirds have to eat close to fifty percent of their weight in food everyday to keep up theirstrength.

蜂鸟每天吃的东西是它们体重的二分之一，这样才能维持体力。

They eat things that are packed with calories and produce lots of reusable energy, likeseeds, nuts, fruit, and nectar.

它们吃的东西都是高热量食物，能产生大量可重复使用的能量，像种子，坚果，水果和花蜜。