Overview

Brief Summary

Biology

Although flying-fish, and possibly squid, feature prominently in the Ascension frigatebird's diet, this highly predatory species is known to take young chicks from the nests of other seabirds as well as newly-hatched turtles on their way to the sea (2) (4). Furthermore, like other frigatebirds, it will harass smaller seabirds into dropping their own food, in a strategy known as kleptoparasitism (3) (4). Breeding occurs year-round, with the frequency of egg-laying increasing from May through to October, before dropping off again (2) (4). During courtship, males come together in relatively passive groups to present their inflated gulars to overflying females. Pointing their ballooning throats towards the sky, each male throbs rhythmically with its wings half extended, and clops its bill noisily (3) (4) (5). After pairing up and copulating, the female lays a single egg in a shallow scrape in the ground, augmented with pebbles, feathers and bones. The young hatch after around 44 days, but only learn to fly after six or seven months, and remain largely dependant on their parents for food for several months after fledging (4) (5). Breeding success is generally low, with a breeding female unlikely to raise more than one chick every two years (2) (4) (5).
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Description

With a large wingspan and light-weight body, the Ascension frigatebird is a masterful glider (2) (3). In common with other frigatebirds, this species has a deeply forked tail, hooked bill, and distinctly pointed wings (3). The adult male is black overall, with a glossy green and purple sheen, but during courtship it develops a bright red gular that inflates to form an impressive heart-shaped balloon. The adult female is more rusty-brown, particularly around the collar and breast, and some individuals have patches of white on the breast and abdomen (2) (4) (5). Although similar in appearance to the females, juveniles are readily distinguished by their conspicuous white heads (4) (5).
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Distribution

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).

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Range

Breeds Ascension I.; ranges to w African coast.
  • Clements, J. F., T. S. Schulenberg, M. J. Iliff, D. Roberson, T. A. Fredericks, B. L. Sullivan, and C. L. Wood. 2014. The eBird/Clements checklist of birds of the world: Version 6.9. Downloaded from http://www.birds.cornell.edu/clementschecklist/download/

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Range

The Ascension frigatebird only breeds on Boatswainbird Island, a steep-sided, flat-topped rock, 250 metres off the coast of Ascension Island in the south Atlantic (2) (5) (6).
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Ecology

Habitat

Habitat and Ecology

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
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breeding on Ascension isl.
  • UNESCO-IOC Register of Marine Organisms
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Depth range based on 1 specimen in 1 taxon.

Environmental ranges
  Depth range (m): 0 - 0
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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The Ascension frigatebird breeds amongst the boulders, outcrops and guano on the bare summit of Boatswainbird Island (2) (4) (5).
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Evolution and Systematics

Functional Adaptations

Functional adaptation

Gular pouch used to attract mate: frigatebird
 

Male frigatebirds attract mates with an elastic, red gular pouch that is inflatable.

     
  "A male frigatebird or Man-o-war bird has selected a suitable nest site and is advertising for a mate by inflating its crimson throat pouch. As soon as the first egg is laid, the pouch will be deflated." (Foy and Oxford Scientific Films 1982:76)
  Learn more about this functional adaptation.
  • Foy, Sally; Oxford Scientific Films. 1982. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J.M.Dent & Sons Ltd, Aldine House, London. 238 p.
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
VU
Vulnerable

Red List Criteria
D2

Version
3.1

Year Assessed
2012

Assessor/s
BirdLife International

Reviewer/s
Butchart, S. & Symes, A.

Contributor/s
Hilton, G. & Ratcliffe, N.

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.

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Status

Classified as Vulnerable (VU) on the IUCN Red List (1).
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Population

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
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Threats

Major 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. 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).

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Following the arrival of humans to Ascension, huge colonies of Ascension frigatebird, that bred on Ascension Island itself, were eradicated by feral cats, introduced rats (Rattus rattus) and human predation (2) (7). For most of the 20th century, the remaining colony on Boatswainbird Island was thought to be declining, but recent research suggests the current population is actually stable at around 12,500 birds (6). Nonetheless, despite its apparent stability, this species has a very limited breeding range, and a low reproductive rate, which, together, make it extremely vulnerable to even small impacts (2) (3). There are current concerns that the operation of a long-line fishery in the area may be killing an unsustainable number of Ascension frigatebirds (2).
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Management

Conservation Actions

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.

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Conservation

Boatswainbird Island is designated a sanctuary, and, as such, is protected from human disturbance (2). Since feral cats were eradicated from Ascension in 2004 several seabird species have returned to the main island (2) (8), leading to speculation that the Ascension frigatebird will eventually do so as well (6). The focus of future conservation measures is to continue monitoring the population through further research and to ensure that the fisheries around Ascension are sustainable (2) (6).
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Wikipedia

Ascension frigatebird

Juvenile

The Ascension frigatebird (Fregata aquila) is a seabird of the frigatebird family Fregatidae which breeds on the tiny Boatswain Bird Island just off Ascension Island in the tropical Atlantic Ocean.

The Ascension frigatebird is a large lightly built seabird with brownish-black plumage and a deeply forked tail. It has a wingspan of around 2 m (6.6 ft). The male has a striking red gular sac which it inflates to attract a mate. The female is slightly larger than the male and has a brown breast-band and sometimes a white belly. They feed on fish taken in flight from the ocean's surface (mostly flying fish), and sometimes indulge in kleptoparasitism, harassing other birds to force them regurgitate their food.

Taxonomy[edit]

The Ascension frigatebird was described by Linnaeus in 1758 in the 10th edition of his Systema Naturae under the binomial name Pelacanus aquilus.[2] His specimen had been collected from the Ascension Island by the Swedish explorer Pehr Osbeck.[3] The genus Fregata aquila formerly included all four species of large frigatebirds but in 1914 the Australian ornithologist Gregory Mathews split off the other three species leaving Fregata aquila to denote the Ascension frigatebird.[3] An analysis of ribosomal and mitochondrial DNA indicates that within the Fregata genus, the Ascension frigatebird is most closely related to the magnificent frigatebird.[4]

Distribution[edit]

The Ascension frigatebird formerly bred on Ascension Island itself, but the colonies were exterminated by feral cats introduced in 1815.[5] The birds nest on a 3 hectares (7.4 acres) plateau region on top of Boatswain Islet which lies 250 m (270 yd) off the northeast coast of Ascension Island.[5] A program conducted between 2002 and 2004 successfully eliminated all the feral cats[6] and as a result, in 2012 two pairs of frigatebirds returned to nest on Ascension Island.[7] In 2014 twelve nests were reported on Letterbox Peninsula at the extreme east end of the island.[8]

As with other frigatebirds, its movements outside the breeding season are little known because of identification problems within this difficult group, but it occurs off west Africa. It feeds on fish and similar surface prey such as small turtles.

A juvenile frigatebird found dying in 1953 in Tiree, Scotland was identified at the time as magnificent frigatebird but the specimen was re-examined in 2002 and found to be an Ascension frigatebird.[9] In July 2013 a juvenile was photographed at Bowmore on the island of Islay in Scotland.[10]

Description[edit]

The Ascension frigatebird is similar in size to the other frigatebirds except the smaller lesser frigatebird. It measures 89–96 cm (35–38 in) in length, has a wingspan of 196–201 cm (77–79 in) and weighs around 1,250 g (2.76 lb).[11] The birds have a white axillary spur and juveniles show a white head, and a distinctly white hind neck with no reddish-brown hue. It has a brown breast band.

Status[edit]

A census of the Ascension frigatebird population on the islet of Boatswain conducted in 2001-2002 recorded around 6,250 breeding females implying a total population of 12,500 birds.[5] This number is similar to an earlier estimate of between 8,000 and 10,000 birds obtained in a study conducted in 1957-1959.[12] The species is classified as "Vulnerable" by the International Union for Conservation of Nature as it breeds on just a single tiny island.[1]

References[edit]

  1. ^ a b BirdLife International (2012). "Fregata aquila". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013. 
  2. ^ Linnaeus, C (1758). Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata. (in Latin). Holmiae:Laurentii Salvii. p. 133. 
  3. ^ a b Mathews, GM (1914). "On the species and subspecies of the genus Fregata". Australian Avian Record 2 (6): 117–121. 
  4. ^ Kennedy, Martyn; Spencer, Hamish G (2004). "Phylogenies of the frigatebirds (Fregatidae) and tropicbirds (Phaethonidae), two divergent groups of the traditional order Pelecaniformes, inferred from mitochondrial DNA sequences". Molecular Phylogenetics and Evolution 31 (1): 31–38. doi:10.1016/j.ympev.2003.07.007. 
  5. ^ a b c Ratcliffe, Norman; Pelembe, Tara; White, Richard (2008). "Resolving the population status of Ascension Frigatebird Fregata aquila using a 'virtual ecologist' model". Ibis 150 (2): 300–306. doi:10.1111/j.1474-919X.2007.00778.x. 
  6. ^ Ratcliffe, Norman; Bella, Mike; Pelembe, Tara; Boyle, Dave; Benjamin, Raymond; White, Richard; Godley, Brendan; Stevenson, Jim; Sanders, Sarah (2010). "The eradication of feral cats from Ascension Island and its subsequent recolonization by seabirds". Oryx 44 (1): 20–29. doi:10.1017/S003060530999069X. 
  7. ^ McKie, Robin (8 December 2012). "Frigatebird returns to nest on Ascension for first time since Darwin". The Observer. Retrieved 10 December 2012. 
  8. ^ Fisher, Ian (23 January 2014). "Ascension frigatebird - the return continues". Royal Society for the Protection of Birds. Retrieved 8 December 2014. 
  9. ^ Walbridge, Grahame; Small, Brian; McGowan, Robert Y (2003). "From the Rarities Committee’s files: Ascension Frigatebird on Tiree – new to the Western Palearctic". British Birds 96 (2): 58–73. 
  10. ^ "Rare Ascension frigatebird recorded on Islay". BBC Highlands & Islands. 7 July 2013. Retrieved 11 July 2013. 
  11. ^ Orta, J; Christie, DA; Garcia, EFJ; Jutglar, F; Boesman, P. "Ascension Frigatebird (Fregata aquila)". In del Hoyo, J; Elliott, A; Sargatal, J; Christie, DA; de Juana, E. Handbook of the Birds of the World Alive. Barcelona: Lynx Edicions. Retrieved 30 November 2014. (subscription required)
  12. ^ Stonehouse, Bernard; Stonehouse, Sally (1963). "The frigatebird Fregata aquila of Ascension Island". Ibis 103b (3): 409–422. doi:10.1111/j.1474-919X.1963.tb06763.x. 
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