27 September 1998

Birds Of A Feather Flock Together

Watching a flock of dozens or even hundreds of birds can be amazing because the separate birds often move as if they possess a single mind. What's more amazing, bird flocks often move harmoniously without any sort of leader or external cue, especially when they are traveling over short distances. Studying bird flocks may seem to be the exclusive domain of ornithologists. But physicists too have become captivated by the remarkable ability of birds--and many other living creatures--to move flawlessly as an organized group.

In the October issue of the journal Physical Review E, John Toner of the University of Oregon and Yuhai Tu of the IBM Watson Research Center in Yorktown Heights, NY present a detailed theory of how birds manage to move together as a single unit, even if the individual birds make frequent misjudgments and can only see an extremely small fraction of the other birds in the flock.

By making a few simple modifications, the authors say that their theory can also describe movements in herds of wildebeest, schools of fish, swarms of bacteria--in short, any collection of independently moving animals that rely on each other's cues to move as a group.

Potentially, their theory can even be applied to the seemingly unrelated topic of automobile traffic flow.

To explain the flocking process, the researchers draw parallels between the motion of flocks and several phenomena in physics: namely, the lining up of magnets, the flow of fluids, and the transfer of heat. But the field of "flocking dynamics" didn't begin in the realm of physics. It didn't really begin in the outdoors. It began in the world of microscopic organisms.