This species is classified as Vulnerable as it breeds on one tiny island where invasion by feral cats is a concern. Censusing the population and ascertaining trends is particularly problematic, but if further data demonstrates a decline, perhaps owing to fishing activities, it may qualify for uplisting to a higher category of threat.
AERC TAC. 2003. AERC TAC Checklist of bird taxa occurring in Western Palearctic region, 15th Draft. Available at: #http://www.aerc.eu/DOCS/Bird_taxa_of _the_WP15.xls#.
del Hoyo, J.; Collar, N. J.; Christie, D. A.; Elliott, A.; Fishpool, L. D. C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Barcelona, Spain and Cambridge UK: Lynx Edicions and BirdLife International.
Distribution and populationFregata aquila
89-96 cm. Large seabird with long wings and long, forked tail. Adult male black overall with glossy green on head and long mantle feathers and bright red gular region which inflates to rugby ball size during courtship. Female dark brown overall with rusty collar and breast. Immature similar to female but has white head. Similar spp. Adult male allegedly inseparable from Magnificent Frigatebird F. magnificens, but female is only female frigatebird with no white on head and body.
now breeds only on Boatswainbird Islet, a flat-topped, steep-sided rock, 250 m off the north-east coast of Ascension Island (St Helena to UK)
in the Atlantic Ocean. Since the early 1800s, when it bred on Ascension Island itself, the population has suffered serious declines and, in 1997, was estimated to lie between 5,000-10,000 individuals (Pickup 1998)
. Current estimates for breeding and mature females are 6,250 and 9,341 respectively, based on census data from 2001-2002; suggesting c.12,500 mature individuals, assuming an equal sex ratio (Ratcliffe et al.
2008). Determining population trends for this species is problematic due to difficulties in carrying out census work, poor baseline information and the high number of mature non-breeders in the population (Pickup 1998, Ratcliffe 1999)
. However, the use of a 'virtual ecologist' model on recent census data, alongside historic data, point to a stable population (Ratcliffe et al.
2008). It probably spends much time far from the island and has been recorded as a vagrant on the west African coast from the Gulf of Guinea to the mouth of the Congo (Ashmole et al.
. Population justification
The current population of mature females is estimated at 9,341 (95% CI: 8,587-10,113), based on census data from 2001-2002, suggesting there may be c.18,682 mature individuals, assuming an equal sex ratio. The confidence intervals for the number of mature females are doubled and rounded to provide a range estimate of 17,000-21,000 for the number of mature individuals, roughly equivalent to 25,000-32,000 individuals in total.Trend justification
It is difficult to determine the current population trend owing to poor baseline information, the difficulties of carrying out census work and the high number of mature non-breeders in the population (Pickup 1998; Ratcliffe 1999).Ecology
It is a surface-feeder, feeding on fish, particularly Cypsilurus
and Flying-fish Exocoetus volitans,
and newly hatched Green Turtles Chelonia mydas
. Breeding occurs in four loose colonies (Orta 1992a)
, mainly on the summit plateau, especially on rougher areas with some groups of birds occupying ledges on the sides of the plateau (Ashmole et al.
. Breeding probably occurs year-round, but there is evidence of some seasonality with laying increasing from May and peaking in October, then declining to a minimum in February-April (Ashmole et al.
. Its clutch-size is one and breeding success is low. Threats
Historically, it has suffered severe declines due to predation by humans, introduced Black Rats Rattus rattus
and most especially feral cats (Ashmole et al.
and there is still a threat of cats reaching Boatswainbird from Ascension Island (Orta 1992a)
. Despite the cat eradication programme that is ongoing on the main island, the species has failed to recolonize the main island in contrast to several other seabird species (Ratcliffe et al.
2008). Since 1988, a Japanese longline fishery has been operating in the area and could be causing significant mortality (Ratcliffe 1999)
although there is no direct evidence for this at present (N. Ratcliffe in litt.
. However, it is known to be caught on baited hooks of the local sport fishery, indicating potential vulnerability to bycatch mortality (Ratcliffe et al.
2008). Possible over-fishing of tuna could be an indirect threat, as predatory fish herd shoals of small fish to the surface where they become available to surface-feeding seabirds (Ratcliffe 1999)
. Conservation Actions Underway
A cat eradication programme has been in operation on Ascension for several years under the guidance of the RSPB and has already resulted in the return of some seabird species to the mainland, although this is not yet the case for Ascension Frigatebirds (N. Ratcliffe in litt.
2000, 2003, G. Hilton in litt
. 2003, Ratcliffe et al.
. Boatswainbird is a bird sanctuary (Orta 1992a)
. Conservation Actions Proposed
Complete and monitor the effects of cat eradication on Ascension. Use independent observers on longline vessels to investigate the numbers of this species killed (Ratcliffe 1999)
. Instigate measures to prevent future mortalities by long-lining if this is proven to be a threat (Ratcliffe 1999)
. Ensure sustainable use of the fisheries around Ascension Island (Ratcliffe 1999)
. Conduct further research on breeding behaviour of marked birds (Pickup 1998)
. Monitor changes in distribution, productivity and long-term population trends.
Ashmole, N. P.; Ashmole, M. J.; Simmons, K. E. L. 1994. Seabird conservation and feral cats on Ascension Island, South Atlantic. In: Nettleship, D.N.; Burger, J.; Gochfeld, M. (ed.), Seabirds on islands: threats, case studies, and action plans, pp. 94-121. BirdLife International, Cambridge, U.K.
IUCN. 2015. The IUCN Red List of Threatened Species. Version 2015-4. Available at: www.iucnredlist.org. (Accessed: 19 November 2015).
Orta, J. 1992. Phaethontidae (Tropicbirds). In: del Hoyo, J.; Elliott, A.; Sargatal, J. (ed.), Handbook of the birds of the world, pp. 280-289. Lynx Edicions, Barcelona, Spain.
Pickup, A. R. 1998. Ascension Island Management Plan.
Ratcliffe, N. 1999. Seabirds on Ascension Island. World Birdwatch 21: 16-18.
Ratcliffe, N., Pelembe, T., White, R. 2008. Resolving the population status of Ascension Frigatebird Fregata aquila using a 'virtual ecologist' model . Ibis 150(2): 300-306.
Further web sources of information
Click here to read about RSPB's work with Ascension Frigatebird on Ascension Island
Explore HBW Alive for further information on this species
View photos and videos and hear sounds of this species from the Internet Bird Collection
Text account compilers
Anderson, O., Benstead, P., Ekstrom, J., Shutes, S., Stattersfield, A. & Taylor, J.
Hilton, G. & Ratcliffe, N.
IUCN Red List evaluators
Butchart, S. & Symes, A.
BirdLife International (2016) Species factsheet: Fregata aquila. Downloaded from
http://www.birdlife.org on 25/08/2016.
Recommended citation for factsheets for more than one species: BirdLife International (2016) IUCN Red List for birds. Downloaded from
http://www.birdlife.org on 25/08/2016.
This information is based upon, and updates, the information published in BirdLife International (2000)
Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004)
Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.
To provide new information to update this factsheet or to correct any errors, please email BirdLife
To contribute to discussions on the evaluation of the IUCN Red List status of Globally Threatened Birds, please visit BirdLife's Globally Threatened Bird Forums.
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