The site comprises the most south-easterly Peninsula of Ascension Island extending east from South East Bay and includes the adjacent coastline to Boatswainbird Island. The site comprises a rugged terrain of a volcanic origin with steep-sided cliffs.
See table for key species. Of the 11 resident seabird species seven breed at this peninsula, including Phaethon aethereus, P. lepturus, Sula dactylatra, S. sula, S. leucogaster, Anous stolidus and Fregata aquila. Oceanodroma castro, Anous minutus and Gygis alba breed on the nearby Boatswainbird Island and it is probable that all three of these species are nesting on the cliff faces on the main island but due to the inaccessible nature of these cliffs this has not been confirmed (Weber, per. comm. 2015). Onychoprion fuscata are present in the area but do not breed at this site. Since the removal of feral cats from Ascension Island from 2002-04 coupled with a seabird recovery programme, F.aquila re-colonised the main island at this site with two nests in 2012-13, these being the first F. aquila nests on the mainland in almost 180 years. Twelve nests were observed at this site in 2013-14 and there were a total of 44 nesting attempts at this site in 2014-15 (Weber, per. comm. 2015). S.dactylatra has also successfully re-colonised the main island after the removal of feral cats, with 20 pairs with eggs and chicks at Letterbox in October 1996, and a single pair on a hill at Georgetown in 1993. This has increased to 3,014 individuals being observed in the early 2015 census (Weber, per. comm. 2015). Both Phaethon aethereus and P. lepturus nest on cliffs opposite Boatswainbird Island and along the south-eastern coast. The current populations of Phaethon aethereus, P. lepturus, S. leucogaster, Anous stolidus at this site were surveyed in 2002 although more recent estimates are currently unknown (largely due to the logistical constraints of cliff surveys) and the population of S. sula is very small. 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: Chelonia mydas (EN), protected locally since 1926, are present in the waters of Ascension as the beaches are important breeding grounds for green turtles and the three main nesting beaches (Long Beach, Pan Am and North East Bay) are designated as Nature Reserves under the National Protected Areas Order, 2014. The dolphin Tursiops truncatus (LC) is common around the island and there are also regular sightings of Stenella attenuate (LC). There is a long list of invertebrates, including historic records of endemic pseudoscorpions Apocheiridium cavicola and Allowithius ascensionis. Yellow and purple land-crabs Johngarthia lagostoma occur throughout the main island, returning to the sea to breed each year. The endemic shrimps Procaris ascensionis and Typhlatya rogersi, are found in anchialine rock pools located 50 – 100m inland with no surface connection to the sea that fall within the area of this Nature Reserve/ IBA. There are also 11 species of coastal fish which are probably endemic to Ascension along with a further 16 fish species which appear to be shared endemics with St Helena (Wirtz et al., 2014). The indigenous flora of Ascension Island is minimal with approximately 25 vascular plants, and 7 endemics, of which 1, the spurge Euphorbia origanoides grows in this IBA area. There are 77 recorded species of bryophytes on Ascension, of which 15 are believed to be endemic to the island.
BirdLife International (2019) Important Bird Areas factsheet: Letterbox Peninsula. Downloaded from http://www.birdlife.org on 26/04/2019.