Why starlings murmur

On winter evenings, just before they roost, thousands of starlings pour across the sky as one shape that folds, splits and heals itself. Nobody is in charge of it.

Each bird watches only its nearest six or seven neighbors and copies their turns. That one small rule, copied fast enough, is all it takes: no bird leads, and yet the whole flock turns as one.

A turn that starts at one edge crosses the whole flock in moments, faster than any single bird could fly across it.

Scientists call it scale-free correlation. Everyone else calls it one of the best free shows on Earth.