Tropic-bird (Phaëthon), a genus of birds of the family Phaëthonidae. The bill is strong, pointed, and almost arched; the head completely feathered; the tail short; the four toes united by a web. In general aspect and size they closely resemble gulls or terns. They often follow in the wake of ships, and are known to sailors as 'Boatswains.' The two very long tail-feathers are in one species red and in the two other species white. Their flight is very unlike the usual flight of sea-birds, its chief peculiarity being the rapid and constant strokes of the wings, more like a duck than a gull. Three species are known, all tropical, and often seen very far from land. They breed in cracks of cliffs or ledges of rock, but make no nest. The Common Tropic-bird (P. aëthereus) is about the size of a partridge, white, with curved lines of black on the back; some of the quill-feathers black, tipped with white. It is found in the Atlantic Ocean. In the Indian and Pacific Oceans another species, the Red-tailed Tropic-bird (P. rubricauda or phaenicurus) appears, which is larger in size, of a deep roseate tinge, with red bill and the retrices and long feathers of the tail red. The Yellow-billed Tropic-bird (P. flavirostris or candidus) is the smallest in size; it breeds in Bermuda, and occurs numerously in the South Atlantic, the Indian, and a great part of the Pacific Ocean.