Ascension Frigatebird (Fregata aquila) - BirdLife species factsheet

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VU	Ascension Frigatebird Fregata aquila

2010 IUCN Red List Category (as evaluated by BirdLife International - the official Red List Authority for birds for IUCN): Vulnerable

Justification 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.

Family/Sub-family Fregatidae

Species name author (Linnaeus, 1758)

Taxonomic source(s) AERC TAC (2003), Dowsett and Forbes-Watson (1993), Sibley and Monroe (1990, 1993)

Identification 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.

Population estimate	Population trend	Range estimate (breeding/resident)	Country endemic?
17,000 - 20,200	unknown	2,800,000 km²	Yes

Range & population Fregata aquila 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 individuals³. The current number of mature females is estimated at 8,587-10,113, based on census data from 2001-2002⁷, suggesting there may be c.18,682 mature individuals, assuming an equal sex ratio. Determining the current population trend is problematic due to difficulties in carrying out census work, poor baseline information and the high number of mature non-breeders in the population^3,4. 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 Congo¹.

Important Bird Areas Click here to view map showing IBAs where species is recorded and triggers any of the IBA criteria.

Ecology: It is a surface-feeder, feeding on fish, particularly Cypsilurus and Hirundichthyes and Flying-fish Exocoetus volitans, and newly hatched Green Turtles Chelonia mydas. Breeding occurs in four loose colonies², mainly on the summit plateau, especially on rougher areas with some groups of birds occupying ledges on the sides of the plateau¹. 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-April¹. 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 cats¹,and there is still a threat of cats reaching Boatswainbird from Ascension Island². Since 1988, a Japanese longline fishery has been operating in the area and could be causing significant mortality⁴ although there is no direct evidence for this at present⁵. Possible over-fishing of tuna could be an indirect threat, as they herd shoals of small fish to the surface where they become available to surface-feeding seabirds⁴.

Conservation measures 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^5,6. Boatswainbird is a bird sanctuary².

Conservation measures proposed Complete and monitor the effects of cat eradication on Ascension. Use independent observers on longline vessels to investigate the numbers of this species killed⁴. Instigate measures to prevent future mortalities by long-lining if this is proven to be a threat⁴. Ensure sustainable use of the fisheries around Ascension Island⁴. Conduct further research on breeding behaviour of marked birds³. Monitor changes in distribution, productivity and long-term population trends.

References 1. Ashmole et al. (1994). 2. Orta (1992a). 3. Pickup (1998). 4. Ratcliffe (1999). 5. N. Ratcliffe in litt. (2000, 2003). 6. G. Hilton in litt. (2003). 7. Ratcliffe et al. (in press).

Text account compilers Phil Benstead (BirdLife International), Jonathan Ekstrom (BirdLife International), Sue Shutes (BirdLife International), Alison Stattersfield (BirdLife International), Joe Taylor (BirdLife International)

Contributors Geoff Hilton (Royal Society for the Protection of Birds), Norman Ratcliffe (Royal Society for the Protection of Birds)

IUCN Red List evaluators Jeremy Bird (BirdLife International), Stuart Butchart (BirdLife International), Rob Calvert (BirdLife International)

Recommended citation BirdLife International (2010) Species factsheet: Fregata aquila. Downloaded from http://www.birdlife.org on 29/7/2010

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.

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