name is derived from Ancient Greek phaethon, "sun", while the species epithet comes from the Latin words ruber "red" and cauda "tail". English ornithologist John Latham wrote about the red-tailed tropicbird in 1785 in his General Synopsis of Birds, recording it as common in Mauritius and the South Pacific. He also reported a black-billed tropicbird collected from Palmerston Island that ended up in Banks' collection. Latham did not give them binomial names, however. It was left to German naturalist Johann Friedrich Gmelin to describe the species, which he did as Phaeton phoenicuros and P. melanorhynchos respectively in the 13th edition of Systema Naturae in 1788. Latham later described this black-billed specimen as the New Holland tropicbird, giving it the name Phaethon novae-hollandiae. The British naturalist Walter Rothschild reviewed the described names and specimens in 1900 and concluded that the original use of P. erubescens was a nomen nudum. He concluded that the populations of Lord Howe, Norfolk and Kermadec Islands belonged to a distinct subspecies which he named P. rubicauda erubescens, due to their larger overall size, more robust bill and prominent reddish tinge to their plumage. He also classified P. melanorhynchus and P. novae-hollandiae as juveniles. The Australian amateur ornithologist Gregory Mathews then applied the name P. rubicauda roseotinctus to Rothschild's P. rubicauda erubescens. "Red-tailed tropicbird" has been designated the official name by the International Ornithologists' Union (IOC). Other common names include red-tailed bos'nbird or silver bos'nbird, the names derived from the semblance of the tail feathers to a boatswain's marlin spikes, and strawtail. The New Zealand Māori call it amokura, and the native Hawaiians koae ula. Its closest relative is the white-tailed tropicbird (P. lepturus), the split between their ancestors taking place about four million years ago. Four subspecies are recognised by the IOC: P. r. rubricauda Boddaert, 1783 the nominate subspecies, from the western Indian Ocean. Subsequent specimens from the Cocos (Keeling) Islands were allocated to this taxon. P. r. westralis Mathews, 1912 from the eastern Indian Ocean. Mathews described it as separate on account of its larger wings. More extensive analysis in 1989 showed that the wing and beak size overlap between this and the nominate subspecies, leaving intensity of colour as the only distinguishing feature. P. r. roseotinctus Mathews, 1926 from the southwestern Pacific Ocean, including populations on Kermadec, Lord Howe, Norfolk and Raine Islands. P. r. melanorhynchos Gmelin, 1789 from the western, central and