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.

BND photojournalist Derik Holtmann recently captured images of a huge flock of birds flying in unison before sunset near Illinois 4 in Mascoutah. A gigantic flock of birds is a familiar site around ...