The three recognized subspecies have varying levels of conservation concern. Of the two that occur in the neotropics, one breeds in the region and the other disperses from the tropical south Atlantic into waters off Brazil.
P. a. mesonauta:
In the Atlantic, the Antillean and Caribbean population has been estimated at only 1600+ (van Halewyn and Norton 1994) to 2,500 pairs (Walsh-McGehee 2000). This increase in the population estimate was based largely on the discovery of 1,000 pairs nesting on Saba and not a result of an actual population increase. Bradley and Norton (2009) revised this to 1,800 nesting pairs. In the Pacific, Red-billed Tropicbirds have not been detected on the Ecuadorian mainland in recent years (Duffy and Hurtado 1984). The population on the Galapagos Islands consists of only a few thousand pairs in 30 colonies (Coulter 1984), the Gulf of California population consists of 350 pairs at 2 colonies, and the numbers of pairs nesting along the Pacific coast of Central and South America are small and perhaps extirpated. In the tropical eastern Atlantic, this subspecies nests on the Cape Verde Islands where their total population is estimated to be less than 500 pairs (de Naurois 1969) and is perhaps as few as 100 pairs. The status of the population on the islands off Senegal is unknown, but believed to be small, and the one in the Madeleine Archipeligo is comprised of 30 pairs. Thus the total neotropical population is likely not to exceed 5,000 pairs of breeding adults and the total Atlantic population is certainly less than 6,000 pairs.
P. a. aethereus:
This southern tropical Atlantic race breeds on only 3 islands. There are an estimated 600 pairs nesting on Ascension (Dorwood 1962), 86 pairs on St. Helena (Edwards et al. 1981) and a few on Fernando Noronha. The total population of this subspecies is well below 1,000 pairs.
This race is found in the Gulf of Suez, the Red Sea, the Persian Gulf, the Gulf of Aden, the Gulf of Oman and the eastern Arabian Sea. No real population assessment is available, but a census on islands off Qatar show the species present on 5 islands with individual islands supporting only 1 to 500 pairs. Likewise surveys in Oman, Saudi Arabia, and Yemen indicate only a few nests on the majority of 12 islands, although one island off Oman supported 200 pairs (Gallagher et al. 1984). Due to its restricted geographic distribution it is likely that this race currently consists of only a few thousand pairs.
(In progress-more information to be added)