听力文摘：自然界的直升机

Nature's Helicopters

自然界的直升机

Most birds flap their wings up and down, but hummingbirds² move their wings in a figure-eight pattern. With each flap they twist their wings one-hundred-eighty degrees so that they create a downward thrust on both the forward and backward strokes.

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。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 hover³. They can go forward, backwards⁴, or sideways by tilting⁵ their wings in the direction they want to go. Kind of like a helicopter.Exactly.

如果每次翅膀旋转的力度一样，蜂鸟就会盘旋在空中。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。就像直升机一样。是的。

In order to hover, hummingbirds have to be really strong. Their wing muscles are thirty percent of their total weight. When a small hummingbird¹ hovers⁶ it flaps its wings about eighty times per second.

要盘旋在空中，蜂鸟必须得很强壮。它们翅膀的肌肉重量占身体整个体重的三分之一。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 their strength. They eat things that are packed with calories and produce lots of reusable energy, like seeds, nuts, fruit, and nectar.

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。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。

1 hummingbird   

n.蜂鸟

参考例句：

• The hummingbird perches on a twig of the hawthorn.小蜂鸟栖在山楂树枝上。
• The hummingbird is the only bird that can fly backward.蜂鸟是唯一能倒退向后飞的鸟。

2 hummingbirds   

n.蜂鸟( hummingbird的名词复数 )

参考例句：

• Hummingbirds have discovered that nectar and pollen are very nutritious. 蜂鸟发现花蜜和花粉是很有营养的。
• Why do hummingbirds and gorillas both have backbones? 为什么蜂鸟和大猩猩都有脊骨？

3 hover   

vi.翱翔，盘旋；徘徊；彷徨，犹豫

参考例句：

• You don't hover round the table.你不要围着桌子走来走去。
• A plane is hover on our house.有一架飞机在我们的房子上盘旋。

4 backwards   

adv.往回地，向原处，倒，相反，前后倒置地

参考例句：

• He turned on the light and began to pace backwards and forwards.他打开电灯并开始走来走去。
• All the girls fell over backwards to get the party ready.姑娘们迫不及待地为聚会做准备。

5 tilting   

倾斜，倾卸

参考例句：

• For some reason he thinks everyone is out to get him, but he's really just tilting at windmills. 不知为什么他觉得每个人都想害他，但其实他不过是在庸人自扰。
• So let us stop bickering within our ranks.Stop tilting at windmills. 所以，让我们结束内部间的争吵吧！再也不要去做同风车作战的蠢事了。

6 hovers   

鸟( hover的第三人称单数 )； 靠近（某事物）； （人）徘徊； 犹豫

参考例句：

• A hawk hovers in the sky. 一只老鹰在天空盘旋。
• A hen hovers her chicks. 一只母鸡在孵小鸡。