Justification of Red List Category
This species has a very large range, and hence does not 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 is very large, and hence does not 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 global population is estimated to number >c.50,000 individuals (del Hoyo et al. 1992), while the population in Japan has been estimated at <c.50 individuals on migration (Brazil 2009).
The population is suspected to be in decline owing to predation by invasive species.
This species can be found across much of the tropical oceans, including the southern Indian Ocean, the western and central Pacific, and the southern Atlantic Ocean. Breeding colonies are also found in the Carribean (del Hoyo et al. 1992).
The white-tailed Tropicbird can be found over pelagic waters and the coast of tropical and subtropical seas. It feeds on small fish, especially flying-fish, squid and some crustaceans (especially crabs). Its diet varies locally; e.g. in the Seychelles, it consists mostly of fish. Most prey is caught by plunge-diving, but flying-fish can be taken on the wing. Breeding occurs seasonally in places, but can also occur aseasonally. The species is loosely colonial, nesting in rocky crevices or sheltered scrape on the ground on small-remote islands. Nests are placed preferably in inaccessible spots on cliffs where take-off is easy. It is resident and dispersive, with both adults and juveniles wandering extensively (del Hoyo et al. 1992).
Hurricanes Dean and Felix, in 1989 and 1995 respectively, caused high levels of mortality of both chicks and brooding adults in Bermuda (Lee and Walsh-McGehee 2000). This also resulted in the elimination of 30-50% of nesting sites along the south shore of Bermuda, as well as making other sites temporarily unusable (Lee and Walsh-McGehee 2000). This loss of nesting sites is considered to be the most significant long-lasting effect of the hurricanes (Lee and Walsh-McGehee 2000), although artificial nesting sites, known as ‘Longtail Igloos’, have been successfully installed in many areas of the Bermuda coast. Birds nesting in these artificial nests had greater breeding success than those in natural nests in the 2009 and 2011 breeding seasons (Madeiros 2011).
Tropicbirds are vulnerable to oil pollution at sea, with 1 in 4 birds showing oil fouling on arrival to Bermuda in the early 1970s (Wingate 1973 in Butler et al. 1973). Oiled birds failed to breed and disappeared from their nesting sites (Wingate pers. comm.). This threat is decreasing; oil pollution peaked in the Sargasso Sea around 1972 and began to decline as a result of new regulations concerning dumping oil at sea (Lee and Walsh-McGehee 2000).Road construction and housing development have impacted tropicbird populations (Lee and Walsh-McGehee 2000). The construction of sea walls, filling in coastal property, and the carving out of cliffs for development have taken their toll on tropicbird populations. Tropicbirds have mostly been reduced to nesting on inaccessible sea cliffs and remote islands and cays (Lee and Walsh-McGehee 2000). However, the Bermudan general public are being encouraged to install ‘Longtail Igloos’ on their private property, which may increase the nesting range of the bird (Department of Environment and Natural Resources 2012).
Text account compilers
Calvert, R., Fjagesund, T., Butchart, S., Hermes, C., Martin, R., Miller, E., Stuart, A., Ekstrom, J.
BirdLife International (2020) Species factsheet: Phaethon lepturus. Downloaded from http://www.birdlife.org on 24/11/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 24/11/2020.