Apart from the “free ride” strategy,scientists were also surprised to observe that migrating birds timed their wing beats and adjusted their positions in a very precise way to maximize the lifting effect while avoiding areas where the air moved downward.

　　“They’re able to sense what’s going on from the bird in front,where this ‘good air’ is coming from and how to position themselves perfectly in it,” lead researcher Steven Portugal told BBC.

　　In fact,the “V” formation has long been thought to help birds fly more efficiently(效率高地).A previous study showed that birds’ heart rates went down when they were flying together in a “V” formation.Jet fighters were also found to be able to reduce their energy use by up to 18% by staying near the wingtips of other jet fighters.Both of these findings led scientists to suspect that the “V” formation had an efficiency purpose,but until now they still lack proof.

　　“For scientists,the new study provides an insight into an interesting natural phenomenon.But it could mean even more for aircraft companies—helping them understand how they can imitate that with their plane formations to save fuel,”said Portugal.

　　【语篇导读】这是一篇说明文。研究人员发现,鸟类在迁徙途中总是排列成V字形,这样做是为了在迁徙途中节省体力。

　　9.What is the author’s purpose in writing this article?

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