Birds in Flight In the sky in Europe, Couzin sees a black blob that keeps shiſt ing shape. It stretches like a ribbon. It ripples like a wave. It swirls like smoke from a fire. It gathers into a ball and then stretches out again. As it gets closer, he hears chirps and the rustle


of millions of flapping feathers. He sees that this black mass is really a flock of starlings. Each bird zips as fast as 64 kph through the air, twisting and turning, yet never bumping into its neighbor. T is flock has no apparent leader. Yet somehow the birds fly and change direction together. Suddenly, a hawk approaches the flock. Hawks


hunt starlings. T e starlings closest to the hawk see it and move away from the danger. So does the entire flock, including the starlings on the far side of the flock. T ey can’t see the hawk. Yet they can see nearby starlings. Each starling watches its six closest neighbors.


If one changes direction, the six closest to it change direction, too. T en the six closest to them turn, and so on. In seconds, the movement ripples across the


flock. T is swarm behavior helps the starlings escape the hawk. All these birds are reacting to what they see, or


electromagnetic inputs. T ey may also respond to other sensory inputs, Couzin says. T ey may feel a change in the way the air flows caused by flapping wings. T ey may hear a change in the way feathers cut through the air. T ey may use all these inputs to fly as a flock.


6 NATIONAL GEOGRAPHIC EXTREME EXPLORER


Thousands of starlings form a ribbon of black in the sky, searching for a roost for the night.


Sardines use visual and other sensory cues to stick together and try to confuse predators.


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