Most birds have to fly long distances to migrate.

大多数的鸟类不得不飞行很长的距离进行迁徙。

《柯林斯英汉双解大词典》

How do birds fly?

鸟儿怎么飞翔？

youdao

Wings help birds fly.

翅膀帮助鸟飞翔。

youdao

And the other part about it is if feathers were twice as heavy, or half as strong, then birds couldn't fly."

VOA: special.2010.06.01

Why,if there was two birds setting on a fence, he would want you to decide which one would fly first so he could win money.

VOA: special.2009.08.29

And hundreds of kinds of birds have been sighted in the park which serves as a stopping area for birds as they fly to other places.

VOA: special.2009.10.30

Unlike shooting partridge in Spain, where the birds fly low due to the landscape, here they are much higher.

WSJ: Scotland's Cawdor Estate

Breeders of homing pigeons have been prevented from letting their birds fly freely.

NPR: China's Bird Flu Response Shows New Openness

According to a 1998 study by Louisiana State University, more than 500 million birds fly over the Gulf and enter the United States along coastal areas in Louisiana and Texas each spring.

CNN: Oil spill could be disaster for animals, experts say