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Fregata aquila

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA AVES SULIFORMES FREGATIDAE

Scientific Name: Fregata aquila
Species Authority: (Linnaeus, 1758)
Common Name(s):
English Ascension Frigatebird, Ascension Is. Frigatebird
French Frégate aigle-de-mer

Assessment Information [top]

Red List Category & Criteria: Vulnerable D2 ver 3.1
Year Published: 2012
Date Assessed: 2012-05-01
Assessor(s): BirdLife International
Reviewer(s): Butchart, S. & Symes, A.
Contributor(s): Hilton, G. & Ratcliffe, N.
Facilitator/Compiler(s): Anderson, O., Benstead, P., Ekstrom, J., Shutes, S., Stattersfield, A., Taylor, J.
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.

Geographic Range [top]

Range Description: 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 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. 1994).

Countries:
Native:
Saint Helena, Ascension and Tristan da Cunha
Vagrant:
United Kingdom
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: 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.
Population Trend: Unknown

Habitat and Ecology [top]

Habitat and 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 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. 1994). 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. 1994). Its clutch-size is one and breeding success is low.

Systems: Terrestrial; Marine

Threats [top]

Major Threat(s): Historically, it has suffered severe declines due to predation by humans, introduced Black Rats Rattus rattus and most especially feral cats (Ashmole et al. 1994),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. 2000, 2003). 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 [top]

Conservation Actions: 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. 2008). 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.


Citation: BirdLife International 2012. Fregata aquila. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 20 December 2014.
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