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When crested¹ pigeons spot a predator², they give a little whistle. But the sound doesn’t come from their beaks³. And according to a study published by The Royal Society, that whistle warns the rest of the flock to flee.

There’s safety in numbers, and a flock offers protection in part because it has so many eyes watching for danger. But it’s not clear how an individual sounds the alarm when it spots a predator. Maybe anytime one or two birds fly off, they all do. Just in case. Of course that kind of knee-jerk reaction could produce a lot of false alarms. So how can birds tell when their flockmates are seriously headed for the hills?

Scientists recorded the sounds made by the wings of crested pigeons during a routine liftoff (wing sound 1). And the noise their wings make during an emergency takeoff (wing sound 2). And they found that the sound make by wings flapped in terror includes a distinctive⁴ sort of whistle.

That noise alone will scatter⁵ a flock of feeding pigeons just as quick as the shadow of a passing hawk⁶. And gives a whole new meaning to the expression, “on a wing and a prayer.”

—Karen Hopkin