When feeding or roosting, shorebirds often pause for a second or two and tilt their heads to the left or right. They're doing this to check they sky above for avian predators, particularly raptors. Species like Peregrine Falcons and Merlin often prey on other birds, so flocks of shorebirds cast a wary eye to the sky to make sure they aren't in the area. Since their eyes are on the side of their heads, birds don't tilt their heads backwards like we do to look up, but tip sideways. Birds recognize the silhouettes of raptors and know which shapes signal danger and which they do not need to be concerned about, so a passing Brown Pelican won't cause a flock to take flight, but when a falcon swoops in, they flush immediately.

On a recent survey of roosting American Oystercatchers, several birds stood in a row and took turns looking up. This continued for the twenty minutes or so that I watched them. No raptor was in sight, but perhaps one had passed by before I arrived and left the flock on edge.

Flocks have this advantage over lone birds, which have only one pair of eyes to keep a look out with, like this Wilson's Plover.

-- Lindsay Addison