Speaking of pied shorebirds as I did yesterday ... when I see American oystercatchers I'm reminded of black skimmers (Rynchops niger). Both have bold black-and-white plumage and long beaks but their differences are striking.
Unlike oystercatchers, skimmers have very short orange legs and a beak whose mandibles are two different lengths. They use their long lower mandible -- 2-3 cm longer than the upper -- to skim food from the ocean's surface in flight. Click here to see.
Black skimmers aren't born like this. At hatching their beaks are normal but by the time they fledge four weeks later their lower mandibles have grown 1 cm longer than the uppers, halfway to this striking adult appearance.
One more amazing beak fact: Black skimmers' beaks look fat from the side but if you see them straight on they are knife-thin like this.
The better to skim with, my dear.
(photo by Steve Gosser)