are sufficiently unique that they have their own order Phaethontiformes containing a single family Phaethontidae and a single genus Phaethon. There are three species in this genus:

Red-billed Tropicbird Phaethon aethereus
(tropical Atlantic, eastern Pacific, and Indian oceans)
Red-tailed Tropicbird, Phaethon rubricauda
(Indian Ocean and the western and central tropical Pacific)
White-tailed Tropicbird, Phaethon lepturus
(widespread in tropical waters, except in the eastern Pacific)