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Ascension Frigatebird | Fregata aquila
Ascensionfregatvogel | Rabihorcado de Ascensión
The Ascension Frigatebird breeds nowhere but Ascension, in the middle of the tropical Atlantic. Off the west coast of southern Africa it is a candidate vagrant: frigatebirds are rarely seen there and are hard to identify to species at sea.
Voice
Silent at sea. At the colony bill-clattering and a harsh, rattling call; displaying males give a trilling, gurgling sound.
Recording: Jim Holmes — CC BY-NC-SA 4.0 · converted to mono · xeno-canto
Identification
89–96 cm long, wingspan about 196–201 cm. A typical frigatebird with narrow, angled wings, long forked tail and long, hooked bill. The male is wholly black with a green gloss on head and mantle and a red gular pouch. The female is dark blackish-brown with a rufous-brown collar and breast band; most females are wholly dark below, a minority show a white patch on the breast. Juveniles have a white head and white belly. The dark-bellied female with a brown breast band is unique among frigatebirds.
Confusion species
Magnificent Frigatebird (Fregata magnificens) is larger; the female has a black throat and a large white breast, the male a purple rather than green gloss. Male Great Frigatebird (Fregata minor) cannot be separated without good views of the gloss and the pale wing bar; the female has a grey-white throat and white breast. Lesser Frigatebird (Fregata ariel) is much smaller and shows white into the armpits.
Habitat
Tropical Atlantic around Ascension; forages over open sea up to hundreds of kilometres from the colony, taking flying fish and turtle hatchlings and robbing other seabirds. Breeds on bare rock.
Where the bird is most at home, classified by the vegetation units of southern Africa.
Range and movements
Not conclusively recorded within the region; reports of frigatebirds at sea off the west coast of South Africa and Namibia may involve this species but are undocumented. Young birds wander widely over the Atlantic after fledging and have been seen off West Africa. The species breeds only on Ascension: for a long time solely on the rock stack of Boatswain Bird Island, and since the eradication of feral cats again on the main island.
How and when to look
Any frigatebird off the west coast deserves photographs from above and below, especially of the head, throat and breast. Only an adult female with a dark belly and rufous breast band can be named with certainty at sea; juveniles and males are almost impossible to identify.
Conservation status
Vulnerable because of its very small breeding base on a single island. Following the eradication of feral cats on Ascension in 2004–2006 the species has returned to the main island and the population is growing; without that colony it would remain exposed to disasters and food shortages.
Scientific name
Fregata aquila | (Linnaeus, 1758)
Linnaeus described the species in 1758 as Pelecanus Aquilus; because it was later moved to another genus, the author and year stand in brackets. The genus Fregata was introduced in 1799 by De Lacépède. Fregata derives from the French frégate, 'frigate', a fast warship — for the swift flight and the habit of robbing other seabirds. aquila is Latin for 'eagle' — for the raptor-like way frigatebirds chase other seabirds for their food. The specimen the first description was based on came from Ascension Island.