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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Depth range based on 1 specimen in 1 taxon.

Environmental ranges
  Depth range (m): 0 - 0
 
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breeding on Ascension isl.
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Depth range based on 1 specimen in 1 taxon.

Environmental ranges
  Depth range (m): 0 - 0
 
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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
2015

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.


History
  • Vulnerable (VU)
  • Vulnerable (VU)
  • Vulnerable (VU)
  • Vulnerable (VU)
  • Vulnerable (VU)
  • Critically Endangered (CR)
  • Critically Endangered (CR)
  • Threatened (T)