A frantic cacophony of loud, rapid birdcalls tells other birds there’s a predator on the prowl. It’s called “mobbing” as birds clamor and dart — back and forth — at the threat. An ongoing study of mobbing and other bird warning behavior suggests that some birds listen in on the warnings of other birds. A wave of warning calls spreads from one hillside to another at more than 100 miles per hour. So vulnerable birds may be clued in to the movements of predators like this Northern Pygmy-Owl, giving them time to take cover. Learn more at BirdNote.org.