The red-billed tropicbird ("Phaethon aethereus") is a tropicbird, one of three closely related species of seabird of tropical oceans. Superficially resembling a tern in appearance, it has mostly white plumage with some black markings on the wings and back, a black mask and, as its suggests, a red bill. Most adults have that are about two times their body length, with those in males being generally longer than those in females. The red-billed tropicbird itself has three subspecies recognized, including the nominate. The subspecies "mesonauta" is distinguished from the nominate by the rosy tinge of its fresh plumage, and the subspecies "indicus" can be differentiated by its smaller size, more restricted mask, and more orange bill. This species ranges across the tropical Atlantic, eastern Pacific, and Indian Oceans. The nominate is found in the southern Atlantic Ocean, the subspecies "indicus" in the waters off of the Middle East and in the Indian Ocean, and the subspecies "mesonauta" in the eastern portions of both the Atlantic and the Pacific Oceans and in the Caribbean. It was one of the many species described by Carl Linnaeus in his 1758 10th edition of "Systema Naturae".