Justification of Red List Category
Although this species may have a restricted range, it is not believed to approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size may be small, but it is not believed to approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
The population is estimated to number 5,000-20,000 individuals, roughly equating to 3,300-13,000 mature individuals.
The population is suspected to be in decline owing to predation by invasive species and unsustainable levels of exploitation.
This species ranges across tropical waters of the Atlantic Ocean, the north-west Indian Ocean and the eastern Pacific. Breeding colonies are found on the Galapagos Islands, Ecuador, off the Pacific coast of Mexico, in the Caribbean, Cape Verde, on islands in the southern Atlantic, and on the coasts of Yemen, Oman and Saudi Arabia (del Hoyo et al. 1992).
This species is found in tropical and sub-tropical seas and is mostly pelagic. It feeds primarily on small fish, especially flying fish, but will also take squid. Most prey is caught by plunge-diving but flying-fish are sometimes taken in flight. Breeding is seasonal in places but can be more or less continuous in others. It is loosely colonial, nesting in rocky crevices, or on the ground on small, remote oceanic islands preferentially on cliffs where take-off is easy. No regular migration is undertaken, although individuals can undergo extensive dispersal out to sea (del Hoyo et al. 1992).
The Red-billed Tropicbird population in Abrolhos National Park (Brazil) are under threat from high rates of predation on eggs and nestlings by invasive House Rats Rattus rattus and Brown Rats R. norvegicus (Sarmento et al. 2014). They are highly vulnerable to rat predation due to laying only one egg, their long incubation period, and the ease with which rodents can access the burrows and crevices in which they nest (Sarmento et al. 2014). This threat is of such a magnitude that this sub-population has a mean probability of extinction of 57.5% and a mean time to extinction of 75 years (Sarmento et al. 2014). However, rat predation only affects a minority of the global population. Red-billed Tropicbirds have also been impacted by road construction and housing development (Lee and Walsh-McGehe 2000), with the construction of coastal housing and sea walls excluding Tropicbirds from previous nesting sites (Lee and Walsh-McGehe 2000).
Text account compilers
Hermes, C., Calvert, R., Martin, R., Miller, E., Fjagesund, T., Stuart, A., Symes, A.
BirdLife International (2019) Species factsheet: Phaethon aethereus. Downloaded from http://www.birdlife.org on 17/11/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 17/11/2019.