Skimmers are Tern-like birds having a very strangely developed bill. The lower mandible is much longer than the upper and very thin, the upper edge being as sharp as the lower. The lower mandible is rounded at the end while the upper is more pointed. Young Skimmers are said to have both mandibles of the same length, the abnormal development not appearing until after flight. Skimmers are very graceful birds, and, as implied by their name, they skim over the surface of the water, rising and falling with the waves, and are said to pick up their food by dropping the lower mandible below the surface, its thin edge cutting the water like a knife. There are four species of Skimmers, only one of which is found in North America.