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Location St Helena (to UK), Ascension Island
Central coordinates 14o 18.44' West  7o 56.14' South
IBA criteria A1, A4i, A4ii, A4iii
Area 5 ha
Altitude 0 - 104m
Year of IBA assessment 2015

Site description The site is a barren, steep-sided trachytic rock, about 340 m by 220 m in size, rising to 104 m, with a relatively flat basaltic top nearly 3 ha in extent, located 305 m north of the eastern part of Ascension Island. The site is heavily overlaid with guano, and there are traces of a guano industry that operated for a short period in the 1920s.

Key Biodiversity See table for key species. The site supports nine of the 11 breeding seabird species of Ascension, these being Hydrobates castro, Phaethon aethereus, P. lepturus, Sula dactylatra, S.sula, S. leucogaster, Fregata aquila, Anous minutus and Gygis alba. A.stolidus is not currently recorded as being present on Boatswainbird Island (although it does offer suitable habitat) but breeds on other small offshore rock stacks from Comfortless Cove to Porpoise Point, and Onychoprion fuscata are numerous in the area, historically with small numbers breeding at this site. There have been no records of O. fuscata breeding since the 1990s with the exception of one pair being recorded in 2001–2002 (Ratcliffe et al., 2009; Weber pers. comm. 2015). For several of the species listed this is the main breeding colony for Ascension Island. This site notably supports c. 99% of the worlds’ population of F.aquila which, despite data discrepancies, has appeared to have remained stable for the last 70 years supporting c. 6,250 breeding females and c. 9,350 mature females from data collected over 2001 - 2002 (Ratcliffe et al., 2009). Studies are currently on-going to reliably update this estimate. A current Darwin Plus project is underway to assess the taxonomic and conservation status of storm-petrels in the South Atlantic. This will clarify whether the storm-petrels nesting on St Helena and Ascension constitute one or more new species. An updated population estimate will be included in this project as H.castro have not been surveyed since 1958-59, mostly due to accessibility issues. Similarly P. aethereus and P. lepturus have not been surveyed since 1958-59 due to accessibility limitations to the cliff face. S.sula has a small population present on BBI with 30 individuals in 1958 and 27 recorded in 2002 (Pelembe, 2006). S.leucogaster had a population of 666 in 2002 in comparison to 900 individuals in 1958 (Pelembe, 2006). A.minutus had a population size of 9,600 individuals in 2002, significantly less than the population of 1958 with 25,000 birds (Pelembe, 2006). Puffinus lherminieri is present in the area, and although not confirmed, it is possible that this species may be breeding on Boatswainbird Island and is assumed to have bred at this site in the past (Ratcliffe et al., 2009).

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 are several invertebrates, including the endemic pseudoscorpions Garypus titanius, Neocheiridium sp. and Stenowithius duffeyi. There are 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).

Populations of IBA trigger species

Species Season Period Population estimate Quality of estimate IBA Criteria IUCN Category
Band-rumped Storm-petrel Hydrobates castro breeding  1958-1959  3,000 individuals  medium  A4ii  Least Concern 
Red-billed Tropicbird Phaethon aethereus breeding  1959  500 breeding pairs  medium  A4ii  Least Concern 
White-tailed Tropicbird Phaethon lepturus breeding  1959  1,000 breeding pairs  medium  A4ii  Least Concern 
Ascension Frigatebird Fregata aquila breeding  2001-2002  12,500 individuals  good  A1, A4ii  Vulnerable 
Masked Booby Sula dactylatra breeding  2001-2002  9,000-9,332 individuals  good  A4ii  Least Concern 
Common White Tern Gygis alba breeding  2015  min 854 individuals  medium  A4i  Least Concern 
A4iii Species group - seabirds breeding  2001-2002  20,000-49,999 individuals  medium  A4iii   

Land use

Land-use Extent (% of site)
fisheries/aquaculture -
nature conservation and research -

Acknowledgements Many thanks to Dr Nicola Weber and Dr Sam Weber for preparing the nomination and for providing data. Data has been collected over a number of years by independent researchers from organisations including the British Ornithological Union, Army Ornithological Society and RSPB, and more recently by the Ascension Island Government Conservation Department. All those involved with the Seabird Restoration Project, largely funded by the FCO, have also contributed to data collection.

References Allan (1962), Ashmole (1962, 1963a, b), Ashmole and Ashmole (1997, 2000), Ashmole, Ashmole and Simmons (1994), Blair (1989), Dorward (1962a, b, 1963), Dorward and Ashmole (1963), Duffey (1964), Hughes (1992b), Hughes et al. (1994), Nash et al. (1991, 1992), Osborn (1994), Packer (1983), Pelembe (2006), Ratcliffe (1997, 2008, 2009), Simmons (1967, 1968, 1970, 1990), Stonehouse (1960, 1962 a, b), Stonehouse and Stonehouse (1963), Weber, pers. comm. (2015).

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Recommended citation  BirdLife International (2016) Important Bird and Biodiversity Area factsheet: Boatswainbird Island. Downloaded from on 23/10/2016

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