They decrease the amount of noisy turbulent  air produced when they flap their wings.

它们减少了拍动翅膀时产生的嘈杂湍流空气量。

" Get in close over the crawler, my Lord; you'll find this interesting." The Duke scowled, busied himself with the controls as they came into turbulent air over the crawler.

“靠近爬行者，大人；您会发现这很有趣。”公爵皱着眉头，忙于操纵控制装置，因为它们进入爬行者上方的湍流空气中。