Fregata aquila 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Aves Suliformes Fregatidae

Scientific Name: Fregata aquila (Linnaeus, 1758)
Common Name(s):
English Ascension Frigatebird, Ascension Is. Frigatebird
French Frégate aigle-de-mer
Taxonomic Source(s): AERC TAC. 2003. AERC TAC Checklist of bird taxa occurring in Western Palearctic region, 15th Draft. Available at: # _the_WP15.xls#.
Identification information: 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.

Assessment Information [top]

Red List Category & Criteria: Vulnerable D2 ver 3.1
Year Published: 2017
Date Assessed: 2016-10-01
Assessor(s): BirdLife International
Reviewer(s): Butchart, S. & Symes, A.
Contributor(s): Brown, J., Hilton, G., Leat, E., Oppel, S., Ratcliffe, N. & Weber, N.
Facilitator/Compiler(s): Anderson, O., Benstead, P., Ekstrom, J., Moreno, R., Shutes, S., Stattersfield, A., Taylor, J.
This species is classified as Vulnerable as it has a very small area of occupancy, with the vast majority of the global population restricted to one tiny island where invasion by feral cats was a concern. Following the cat eradication on the adjacent main island of Ascension, this risk has now been substantially reduced. Censusing the population and ascertaining trends is particularly problematic. There is currently no evidence that this species qualifies for for a different threat category.

Previously published Red List assessments:

Geographic Range [top]

Range Description:

Fregata aquila breeds predominately 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, but has re-colonised the main island of Ascension in 2012 following successful cat eradication in 2006. 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). The most recent estimates for breeding and mature females are 6,250 and 9,341 respectively, based on census data from 2001-2002; suggesting c.18.682 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). The small population that re-established on mainland Ascension in 2012 grew rapidly from 2 pairs in 2012 (of which 1 chick successfully fledged) to >100 pairs in 2016, and is expected to grow further as more birds re-distribute from Boatswainbird Island.

At sea, the species forages generally within a 400-600 km radius around Ascension, but satellite tracking indicates use of the Atlantic Ocean to the coast of Brazil. It has been recorded as a vagrant in the UK, and on the west African coast from the Gulf of Guinea to the mouth of the Congo (Ashmole et al. 1994). 

Countries occurrence:
Saint Helena, Ascension and Tristan da Cunha (Ascension)
Brazil; United Kingdom
Additional data:
Estimated area of occupancy (AOO) - km2:1Continuing decline in area of occupancy (AOO):No
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:2620000
Continuing decline in extent of occurrence (EOO):NoExtreme fluctuations in extent of occurrence (EOO):No
Number of Locations:2Continuing decline in number of locations:No
Extreme fluctuations in the number of locations:No
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.

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).

Current Population Trend:Unknown
Additional data:
Number of mature individuals:17000-21000Continuing decline of mature individuals:Unknown
Extreme fluctuations:NoPopulation severely fragmented:No
No. of subpopulations:1Continuing decline in subpopulations:Unknown
Extreme fluctuations in subpopulations:NoAll individuals in one subpopulation:Yes
No. of individuals in largest subpopulation:100

Habitat and Ecology [top]

Habitat and Ecology:

It is a surface-feeder, feeding on fish, particularly Flying-fish Cypsilurus, Hirundichthyes and Exocoetus volitans, and newly hatched Green Turtles Chelonia mydas. Breeding occurs in four loose colonies (Orta 1992a), mainly on the summit plateau of Boatswainbird Island, especially on rougher areas with some groups of birds occupying ledges on the sides of the plateau (Ashmole et al. 1994). Since 2012 a new colony has formed on the south-west facing slope of Letterbox, a volcanic headland < 1 km from Boatswainbird Island. Over the past 4 years this colony(ies) has grown in size both in terms of number of breeding individuals (2 to >100) and also the area covered. Breeding is recorded 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 (50:50). 

Systems:Terrestrial; Marine
Continuing decline in area, extent and/or quality of habitat:No
Generation Length (years):15.5
Movement patterns:Not a Migrant
Congregatory:Congregatory (and dispersive)

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 very small threat of cats reaching Boatswainbird from Ascension Island (Orta 1992a), although this  has been minimised by the successful cat eradication in 2004. After the cat eradication programme on the main island, the species required 10 years to recolonize the main island in contrast to several other seabird species (Ratcliffe et al. 2008). Since 1988, a predominantly Taiwanese and 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
Following the cat eradication programme, Ascension is maintained free of feral cats by enforcing a strict sterilisation regulation for all domestic cats, and by severely limiting the number of domestic cats that can be brought to the island, which are regulated through a cat registration database. Boatswainbird is a Sanctuary under local legislation (National Protected Areas Ordinance 2015), and the adjacent colony on Letterbox (also protected as a Nature Reserve under local legislation) is closely monitored. In 2016 the Ascension Island Government committed to protecting 50% of its Exclusive Fishing Zone as a marine sanctuary, excluding all commercial international fishing.

Conservation Actions Proposed
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. Educational awareness with local recreational fishers on how to safely release hooked birds. 

Amended [top]

Amended reason: Map revised. Edited: Rational Assessment, Geographic Range, Number of Locations, Habitat and Ecology, Countries of Occurence, Threats, Conservation Actions Proposed, Underway and In Place and Important Conservation Actions Needed. Added new Contributors and a new Compiler.

Citation: BirdLife International. 2017. Fregata aquila (amended version of 2016 assessment). The IUCN Red List of Threatened Species 2017: e.T22697728A110667963. . Downloaded on 19 September 2018.
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