Most of the alarms calls were omni-directional, which could be useful in warning other birds of a predator in the vicinity. But some of the bird species -- juncos, warblers and finches -- demonstrated "an ability to focus their calls in the direction of the owl, so these calls could also function to warn off a predator."
Among the birds with this ability, some could sound the alarm in one direction while their heads were turned in a different direction, like a person talking out of the side of his mouth.
"It's not clear how they're accomplishing this," Yorzinski said.
Link via It's Animals
Photo of yellow-rumped warbler courtesy Stockphoto/Franck Leung