Scientists have gained new aerodynamic insight into why many species of birds fly in a V formation. The results, published in the journal Nature, suggest that the distinctive formations are the result of each bird catching a little lift from the bird ahead.
You may have heard that flocks fly in the shape of a V to save energy — like bicycle racers. Since as early as the 1920s, scientists have assumed the same thing. But they didn't have any proof.
"All it was, was theory — no one was ever actually able to measure anything," says Steven Portugal, a researcher at the Royal Veterinary College in London.
For a long time, the main problem was that the technology to measure things like a bird's position or vital signs was just too heavy to be put on the back of a flying animal. But the computer age has changed all that.
Portugal is a member of a lab that's built special devices small and light enough to fit on a bird's back. These gadgets have GPS and accelerometers to measure position and flapping. But they don't have transmitters. The only way to get the data out is to take the device off the bird.
So Portugal had to find a special flock — one that flies in a V, but lands in a predictable place, and whose members don't mind getting handled by people.
The Northern bald ibis is not the world's most attractive bird, but it does, ahem, fit the bill. It hasn't been found in Europe in the wild for more than 300 years, and now conservationists are trying to hand-rear a new generation. Right after hatching, baby ibises are assigned human foster parents. Once the ibises are big enough to fly, the foster parents hop aboard a microlight aircraft and teach the birds where to go. "They teach them the migration routes that they're doing historically," Portugal says.
These birds are perfect for study, because they take off and land whenever the plane does, and they don't mind being touched by people. On top of it all, they naturally organize themselves into a V formation.
"When they first start flying around ... they will naturally put themselves in a V formation," Portugal says. Because the birds are young, those early formations may not be great, he adds. "But it seems like with practice, they gradually get better and better at flying in a good V."
By comparing the birds' flight data to computer simulations, Portugal found that the ibises are apparently drafting — catching an uprush of air from the wingtip of the bird ahead. "Furthermore, when they're in that position, they time wing beats perfectly," he says. "So they don't just sit there passively hoping to get some of the good air from the bird in front."
They actually flap along the perfect sweet spot. Portugal thinks there's a very good reason why the ibises do this. Previous studies have shown that flying is hard work.
"When we get exercising, our heart rate gets up to around 180 beats per minute on a good day," Portugal says. "When birds are flying, it goes up to 400 beats per minute."
But not everyone believes that the questions around V-formation flight have been solved. Michael Dickinson, a flight researcher at the University of Washington, says that the research does confirm theoretical predictions about how birds can save the most energy. But, he says, it doesn't directly measure whether the birds are having to work less hard — the team didn't measure heart rate. "Although this is a cool study, it is not a smoking gun," he says.
AUDIE CORNISH, HOST:
If you've ever looked at a flock of birds passing overhead, you've probably noticed that they tend to travel in the shape of a V. Well, scientists writing in today's issue of the journal Nature say they now know why. NPR's Geoff Brumfiel has this story of high-flying research.
GEOFF BRUMFIEL, BYLINE: You may have heard that birds fly in V's to save energy, that they're drafting like bicycle racers. And for a long time, scientists have thought the same thing. But they didn't have any proof.
STEVEN PORTUGAL: All it was was theory. No one ever actually was able to measure anything.
BRUMFIEL: That's Steve Portugal from the Royal Veterinary College in the U.K. Portugal is part of a lab that's built special devices that can fit on a bird's back and record the stuff you need to know if you're into bird physics. These gadgets have GPS and accelerometers. But they don't have transmitters. The only way to get hold of the measurements is to take the device off the bird's back.
And this meant Portugal needed just the right birds to study formation flying: birds that fly in a V, take off and land in a predictable place, who don't mind getting handled by people. And that's where these guys come in.
(SOUNDBITE OF NORTHERN BALD IBIS)
BRUMFIEL: Meet the Northern bald ibis. That's its mating call, and it looks about as ugly as it sounds.
PORTUGAL: Only a mother could love them, perhaps. But they are - they're very endearing. And they're just a bit different.
BRUMFIEL: Actually, the Northern bald ibis has a lot of fans in Europe. It disappeared from the wild there more than 300 years ago, and now, conservationists are trying to bring it back.
(SOUNDBITE OF BIRDS CHIRPING)
BRUMFIEL: These baby ibises are given human parents right after they hatch.
PORTUGAL: The human foster parents spend every day, every waking moment of every day with the ibis.
BRUMFIEL: Once the ibises are big enough to fly...
PORTUGAL: Then these foster parents hop in a Microlite, these little lightweight planes that you sort of see roaming around. And the birds then follow the Microlite because they're following their foster parent. And they teach them the migration routes that they would have done historically.
BRUMFIEL: OK. So these birds are the perfect test birds. And, as it turns out, they naturally organize themselves into a V formation.
PORTUGAL: When they first start flying around, they will naturally put themselves into a V formation, but it won't be great. But it seems like with practice, they gradually get better and better at flying in a good V.
BRUMFIEL: Portugal and his colleagues put their gadgets on the ibises. Then they compared the data to computer simulations. And the birds are drafting. They catch an uprush of air from the wing tip of the bird ahead. What's more, the birds were synchronizing their wing beats to maximize the effect. Portugal thinks there's a very good reason why the ibises do this. Flying is harder work than, say, running.
PORTUGAL: When we get exercising, our heart rate goes up to about 180 beats per minute on a good day. When birds are flying, it goes up to 400 beats per minute.
BRUMFIEL: Because they're working so hard, Portugal says he thinks ibises notice right away when they're catching a little lift from the bird ahead.
PORTUGAL: Suddenly they hit a spot where they can sense that they're not having to work as hard, and then they go, oh, this feels a bit easier. I'll stay here. And then if all the other individuals are doing the same, eventually they'll create a V formation.
BRUMFIEL: This isn't the end of the research, though. There are still more questions to be answered, like who's the bird that gets stuck at the front? Geoff Brumfiel, NPR News. Transcript provided by NPR, Copyright NPR.