Ascension Frigatebird

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).

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).

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).

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

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

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).