When the front bird moves its wings up and down, the resulting force of the air lifts the next one.

当前面的鸟上下移动它的翅膀时，产生的空气力会带动下一只鸟。

youdao

The bird fluttered its wings up and down.

那只鸟上下地拍动翅膀。

youdao

A ladybug in flight beats its wings up to 85 times per second.

瓢虫飞行时每秒钟扇动翅膀85次。

youdao

Voyager's long wings moved up and down as the winds changed.

VOA: special.2010.10.06

"Some are just sweeping and cleaning,carrying things. Other people,as you can see, are way up high up on the scaffolds putting wings on the eagles.

VOA: standard.2009.12.30

But it appears to be a catalyst-driven chemical system that releases both heat and gas in sufficient quantities to pump the wings up and down.

ECONOMIST: A personal eye in the sky

We pull (the wings) up, pull them down, add weight to them and take them right to the point of breaking.

CNN: SHARE THIS

Its four carbon fiber and foil wings beat up to 20 times per-second, propelling it through the air as if it were swimming rather than flying.

ENGADGET: BionicOpter dragonfly drone flutters about, blows minds