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.
hide captionA flock of Northern bald ibises forms a flying V.
Courtesy of Markus Unsöld
A flock of Northern bald ibises forms a flying V.
Courtesy of Markus Unsöld
"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.