Flocks of birds can get only so big before falling apart. A new study shows that flocks of different sizes behave differently, and could help explain how animals like birds and fish coordinate their movements. Previous work has shown that in large flocks, changes in distance between members propagate rather like sound waves. Now a study by Andrea Cavagna of the Sapienza University in Rome and colleagues has found that changes in flying direction also spread like a wave, but dampen more quickly - as if moving through mud rather than air.
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