One of three bird species, genus Rhynchops, in which the lower mandible of the bill is longer and flatter than the upper, and fits into it like a penknife blade into its handle. They are found on inland and coastal waters in the tropics, and are related to the gulls and terns. They feed on small fish and other aquatic life taken from just below the surface of the water by skimming it with the beak, hence their name.