Any of three species (family Rynchopidae) of waterbirds having a red bladelike bill, with the lower mandible longer than the upper. Skimmers live chiefly in estuaries and along wide rivers in warm regions. At twilight, they skim calm, shallow water with the open bill tip submerged; when a fish or crustacean is hit, the upper mandible snaps down. Skimmers are dark above with white underparts, face, and forehead, red legs, and black wings. The American black skimmer (Rynchops nigra) grows to 20 in. (50 cm) long.