The site comprises the whole of Ascension Island and the 14 inshore stacks, as well as the marine habitat out to three nautical miles, and is described in the ‘General introduction’.
See Box for key species. At least 30 bird taxa are known. There are 11 resident seabird species, Oceanodroma castro, Phaethon aethereus, P. lepturus, Sula dactylatra, S. sula, S. leucogaster, Fregata aquila, Sterna fuscata, Anous stolidus, A. minutus and Gygis alba. Of these, O. castro and F. aquila now breed only on Boatswainbird Island (SH002), but the latter occurs regularly on the main island and both are expected to return as breeders once feral cats are eradicated. In addition, Puffinus lherminieri is thought to have once bred. The main colonies of S. fuscata, by far the most numerous breeding species, are in the south-west of the island, and occupied 9.14 ha in 1997.Although now deserted, many former seabird breeding sites are likely to be reoccupied following the removal of cats. Already, successful recolonization attempts by Sula dactylatra have been noted, e.g. 20 pairs with eggs and chicks at Letterbox in October 1996, and a single pair on a hill at Georgetown from 1993. Both Phaethon aethereus and P. lepturus nest on cliffs opposite Boatswainbird Island and along the south-eastern coast. Anous minutus breeds at Spire Beach, Letterbox, South-east Bay and Cocoanut Bay, while Gygis alba breeds on cliffs inland at Green Mountain and Weatherpost, as well as at South-east Head and opposite Boatswainbird Island. The stacks are important for Anous stolidus (500 pairs) which does not breed on Boatswainbird Island, and also Sula leucogaster and A. minutus.There are five resident landbirds, all introduced; Francolinus afer (introduced 1851), Acridotheres tristis (introduced 1879 and 1880), Passer domesticus (introduced 1985 onwards, Georgetown only), Estrilda astrild (introduced 1860) and Serinus flaviventris (introduced 1890). There are also records of non-breeding visitors and vagrants with fewer than five records. The former include Bubulcus ibis, Gallinula chloropus, Arenaria interpres, Apus apus, Hirundo rustica, and Delichon urbica. In the fossil record, two species are known, an extinct night heron Nycticorax nov. sp. and the extinct flightless rail Atlantisia elpenor.
Non-bird biodiversity: The beaches of Ascension are important breeding grounds for turtles, Chelonia mydas (EN), protected locally since 1926. Hatchlings are taken by feral cats. There is a long list of invertebrates, including two endemic pseudoscorpions Apocheiridium cavicola and Allowithius ascensionis. Yellow and purple land-crabs Gecarcinus lagostoma occur throughout the main island, returning to the sea to breed, laying in shell-sand or soft ash. A shrimp Procaris ascensionis, found in coastal rock pools, is endemic.
BirdLife International (2020) Important Bird Areas factsheet: Ascension Island: mainland and stacks. Downloaded from http://www.birdlife.org on 14/08/2020.