Scientists have found that birds position themselves and time their wing beats so perfectly that, according to aerodynamic theory, they minimize their energy use. It's a task that requires each bird to monitor subtle changes in its wing mates' flight and alter its own path and stroke accordingly.At the end of the video at the link a researcher muses over the question why smaller birds don't also fly in v-formations. My theory is that perhaps large birds use this pattern, in part, to take advantage of the aerodynamic benefits, but also to avoid collisions with other birds in traffic. By aligning themselves with regular spacing they diminish the chances of banging into surrounding members of the flock which would be catastrophic for large flyers like geese and swans.
The new results "once again remind us that animals are much more complicated … than we often give them credit for," says Kenny Breuer, a professor of engineering and ecology at Brown University who was not involved with the study. "They're reacting in very sophisticated ways to maintain these V formations."
Aircraft can save fuel by flying in a V, leading scientists to predict how closely bunched birds in a V-shaped flock should be to save the most energy. But it's no easy feat to measure the coordinates of a bunch of geese or gulls flying fast and high overhead. "It's not something you can do with a pair of binoculars and timing it 'one Mississippi, two Mississippi,' " says study author James Usherwood of Britain's Royal Veterinary College.
When the researchers analyzed the data from 14 young ibises flying in a V, they found that each ibis placed itself an average of four feet behind the bird in front of it and at an average angle of 45 degrees. That's just the configuration needed for individual birds to catch the rising air generated by the flapping of the bird in front of it. By capturing this rising air, or "upwash," the bird stays aloft more efficiently.
But the birds do more to save their strength than simply choosing the right spot. Measurements of the ibises' flaps showed the birds time their wing beats so precisely that they continually catch the upwash left behind by the moving wings of the guy or gal ahead. That means a bird regulates its stroke so its own wingtips trace the same path in the sky as the bird in front. If a bird happens to get a little closer to or farther from the bird it's following, it instantly adjusts its wing beat accordingly, the researchers report in this week's Nature.
Smaller, less massive birds are able to react and maneuver much more quickly than large birds, which means the smaller birds can fly in tight flocks without colliding with their neighbors. Moreover, it may be that smaller birds don't create the air turbulence that bigger birds do so the aerodynamic benefits of flying in a formation are probably not as great for the smaller birds.
I have not a shred of scientific evidence to back any of this up, of course, but that's my theory and I'm sticking to it.
Here's a video of a starling murmuration that shows smaller birds maneuvering and reacting to each other in ways that appear instantaneous and which make collision avoidance seem almost miraculous:
