Ascension frigatebird (Fregata aquila)

Also known as: Ascension Island frigatebird
  
French: Frégate aigle-de-mer
KingdomAnimalia
PhylumChordata
ClassAves
OrderPelecaniformes
FamilyFregatidae
GenusFregata (1)
SizeLength: 89 - 96 cm (2)

The Ascension frigatebird is classified as Vulnerable (VU) on the IUCN Red List (1).

With a large wingspan and lightweight body, the Ascension frigatebird (Fregata aquila) 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 Ascension frigatebird 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).

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).

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

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).

The Ascension frigatebird breeds 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 Ascension frigatebirds hatch after around 44 days, but only learn to fly after six or seven months, and remain largely dependant on the adults 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).

Following the arrival of humans to Ascension, huge colonies of Ascension frigatebirds which 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 that the current population is actually stable at around 12,500 birds (6). Nonetheless, despite its apparent stability the Ascension frigatebird 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).

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).

For more information on the Ascension frigatebird and other bird species, see:

To find out more about the conservation of seabirds on Ascension Island, see:

Authenticated (16/3/09) by Dr Norman Ratcliffe, Vertebrate Ecologist, British Antarctic Survey.
http://www.antarctica.ac.uk/

  1. IUCN Red List (December, 2008)
    http://www.iucnredlist.org/
  2. BirdLife International (February, 2008)
    http://www.birdlife.org/datazone/speciesfactsheet.php?id=3844
  3. Burton, M. and Burton, R. (2002) International Wildlife Encyclopedia. Marshall Cavendish, New York.
  4. Nelson, J.B. (2005) Pelicans, Cormorants and their Relatives. Oxford University Press, Oxford.
  5. Stonehouse, B. and Stonehouse, S. (1963) The frigate bird Fregata aquila of Ascension Island. Ibis, 103: 409-422.
  6. Ratcliffe, N., Pelembe, T. and White, R. (2008) Resolving the population status of Ascension Frigatebird Fregata aquila using a 'virtual ecologist' model. Ibis, 150(2): 300-306.
  7. Procter, D. and Fleming, L.V. (1999) Biodiversity: the UK Overseas Territories. Joint Nature Conservation Committee, Peterborough, UK.
  8. Ascension Conservation (February, 2008)
    http://www.ascensionconservation.org.ac/projects.htm