Most people would say they are doing it to save energy, which would be correct. But it turns out that birds in a V are actually performing an accomplishment that is more complicated and impressive than anyone had imagined.
Here is the standard explanation for the V formation:
When a bird flutters, a rotating vortex of air rolls off each of its wing tips. These eddies cause the air directly behind the bird to be constantly pushed downwards (downwash) and the air behind and to the sides is pushed upwards (upwash). (See this picture if that’s not clear.) When another bird is flying in one of these updraft zones, it is given free lift. It can save energy by blocking the flow of air created by its flock companion.
All of this makes sense, but it represents decades of largely theoretical work. Scientists have calculated how air should flow around a flying bird based on what we know about airplanes, but almost no one had taken actual measurements. Henri Weimerskirch changed that in 2001 when he equipped Pelikans with heart rate monitors. He found that birds in the back of the V had slower heart rates than those in front and fluttered less often.
It was an interesting study that confirmed that birds benefit from flying in a V. But she didn’t deal with why or how they do it. Steven Portugal wanted to know.
First he needed the right technology. His colleagues at the Royal Veterinary College in the UK developed tiny data loggers that are light enough to be carried by a flying bird and sensitive enough to record position, speed and course several times a second.
The devices had a problem: they don’t emit any information. For example, if you strap them to a flock of geese, the birds fly into the distance with very expensive equipment. “We needed a system where birds actually migrate instead of flying in a wind tunnel, but where we can get the data loggers back!” Says Portugal.
Johannes Fritz had a solution. He works for an Austrian nature conservation organization that is trying to save the Northern Bald Ibis – an endangered species that makes vultures look pretty. The ibis became extinct in Central Europe in the 17th century and Fritz is trying to bring it back to its old range. His team has raised several teenagers and teaches them to fly on their ancient migration routes by leading them in a microlight.
The herd of people / ibis stops at fixed points along the route, and a support team follows them on the ground. This gave Portugal many opportunities to equip the birds with loggers, to record every wing beat over long distances and to call up the data a few hours later.
The recordings showed that the bird flies exactly where the theoretical simulations predicted it: about one meter behind the bird in front and another meter to the side. Some ibises prefer to fly to the right of the V or to the left. Some preferred the center, others the edges. But, by and large, the birds traded a lot, and the flock did not have a permanent leader.
But flying in a V is not just about staying in the right place. It’s also about flutter at the right time.
As each bird flaps its wings, the updraft left by its wing tips also moves up and down. The birds behind can somehow sense this and adjust their own flapping to keep their own wings in this free-lift movement zone. “They follow the same path that the bird pulled through the air in front of them,” explains Portugal.
Imagine a flying ibis leaving a red trail with its left wing tip as it moves through the air. The right wing tip of the bird behind it would travel almost exactly the same distance. “It’s like walking through the snow as a child with your parents,” says Portugal. “If you follow their footsteps, they will make your work easier because they crunched the snow.”
This is a far more active process than Portugal assumed. “We thought they were about in the right range and hit the air about 20 percent of the time,” he says. “Actually, they keep track of the good air throughout their flap cycle. We didn’t think they could. It’s quite an achievement. “
The ibises can also change their behavior very quickly. When they change places in the herd, they sometimes find themselves right behind the bird in front and get caught in its downdraft. When that happens, change your punch to do it the contrary of what the bird is doing in front. Instead of following the same path with its wing tips, it flies almost perfectly out of phase. “It’s almost like taking evasive maneuvers,” says Portugal. “They seem to be able to respond instantly to the wake that hits them.”
How do you manage? Nobody knows. The simplest answer is that they just watch the bird in front of them and flap their wings accordingly. You could use their wing feathers to feel the airflow around them. Or they just rely on simple positive feedback. “You fly around, hit a place that feels good and think: Oh, hey, when I flutter like that, it’s easier,” says Portugal.
Whatever the answer, it is clear that this is not a skill the ibises were born with. When they first followed the microlight, they were everywhere. It took them a while to learn to fly in a V … and that adds one final surprise to the mix.
“It was always assumed that the V-formation flight was learned from the adult birds,” says Portugal. “But these guys are all the same age and learned to fly from someone in an microlight. they learned [V-formation flying] from mutual. It’s almost self-taught. “
Relation: Portugal, Hubel, Fritz, Heese, Trobe, Voelk, Hailes, Wilson & Usherwood. 2013. Upwash exploitation and downwash avoidance through valve phase adjustment in ibis formation flight. Nature http://dx.doi.org/10.1038/nature12939
More about Portugal’s work: Scientist spills water and discovers self-cleaning bird egg