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Flocks That Fly as One

You’ve all seen it. Flocks of pigeons in the city wheeling and turning as one. Sandpipers at the beach doing the same thing. You watch in amazement, wondering how they do it. Are they following a leader? Is there some other mysterious force keeping them in unison? If you’re baffled, you have company. For years animal behaviorists have pondered how hundreds and even thousands of birds in a flock move and turn as one. Now someone has come up with an answer​—Wayne K. Potts, biologist at the University of Washington, writing in the scientific journal Nature.

The birds are reacting like a chorus line. Slow-motion films have shown that dancers in a chorus line react to an unrehearsed change in tempo faster than if they just picked it up from their neighbor. The tempo change propagates down the line twice as fast as it would from a visual cue from her neighbor. The dancer sees the change coming before it arrives and adjusts her tempo to the new beat. Slow-motion film studies of flocks of thousands of sandpipers reveal that they do the same thing. The turn may be initiated by a single bird, from any position in the flock. Nearby neighbors respond within 15 thousandths of a second, but when the wave spreads out through the whole flock, it travels at speeds “three times higher than would be possible if birds were simply reacting to their immediate neighbors.” And this happens even if the bird that initiates the change is in the back of the flock!