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 is extremely 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 >1,000,000 individuals (del Hoyo et al. 1992). National population sizes have been estimated at <100 breeding pairs and <50 individuals on migration in Taiwan and <100 breeding pairs and <50 individuals on migration in Japan (Brazil 2009).
The population is suspected to be in decline owing to habitat loss, predation by invasive species and unsustainable levels of exploitation.
This species winters on tropical islands in most oceans, excluding the eastern Atlantic. It winters at sea in the same area, ranging north of the Tropic of Cancer and south of the Tropic of Capricorn (del Hoyo et al. 1992).
This species is strictly marine and largely pelagic. It feeds mainly on flying-fish and squid with a mean prey length of 8.8 cm. Prey is caught by plunge-diving, but flying fish are also taken in flight, especially when chased by underwater predators. It often rests on boats using them as vantage points. Breeding is not seasonal in most of its range. Individuals form large colonies, nesting and roosting mainly in trees or on islets with abundant vegetation (del Hoyo et al. 1992).
The Red-footed Booby continues to be illegally hunted for food in the Cocos Islands despite legislative protection, with around two to three thousand birds estimated to be killed most years (Baker et al. 2004, Carboneras et al. 2018). A certain level of hunting is likely to take place in numerous other small Pacific colonies. However, this does not seem to be significantly affecting the population nesting there (Baker et al. 2004). Clearance of nesting trees for fuel wood or land conversion has occurred on many islands throughout the range, reducing nesting sites available to the species (Carboneras et al. 2018), but again this does not appear to have had much impact on populations of this widespread species.
Text account compilers
Ekstrom, J., Calvert, R., Martin, R., Miller, E., Butchart, S.
BirdLife International (2019) Species factsheet: Sula sula. Downloaded from http://www.birdlife.org on 26/03/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 26/03/2019.