The Physics Of The Flying V

Scientists have figured out how and why birds stay in formation:

[F]lying in a V isn’t just about staying in the right place. It’s also about flapping at the right time. As each bird flaps its wings, the trail of upwash left by its wingtips also moves up and down. The birds behind can somehow sense this and adjust their own flapping to keep their own wings within this moving zone of free lift. “They trace the same path that the bird in front traced through the air,” explains Portugal. Imagine that a flying ibis leaves a red trail with its left wingtip as it moves through the air. The right wingtip of the bird behind would travel through almost exactly the same path. “It’s like walking through the snow with your parents when you’re a kid,” says [Steven] Portugal. “If you follow their footprints, they make your job easier because they’ve crunched the snow down.”

This is a far more active process than what Portugal had assumed. “We thought they’d be roughly in the right area and hit the good air maybe 20 percent of the time,” he says. “Actually they’re tracking the good air throughout their flap cycle. We didn’t think they could do that. It’s quite a feat.”