Migrating birds fly in a V-formation to take advantage of the aerodynamic effects of flying behind another bird. Remarkably, birds take turns at the front despite no obvious benefit to the individual.

The dark, smudgy streaks on Xavi Bou's photographs suggest the jerky ink tracks created by a malfunctioning printer, but they actually record the various patterns birds trace while flying in flocks.

Watching starling murmurations as the birds swoop, dive, and wheel through the sky is one of the great pleasures of a dusky winter’s evening. From Naples to Newcastle, these flocks of agile birds are ...