The site comprises the whole of Tristan Island, as described in the ‘General introduction’.
See Box and Table 2 for key species. Although as many as 56 bird taxa have been recorded, there are now only 13 known species of breeding seabirds and two species of resident landbirds. The seabirds include Eudyptes chrysocome moseleyi, Diomedea chlororhynchos, Phoebetria fusca, Pterodroma macroptera, P. mollis, P. incerta, Pachyptila vittata, Procellaria cinerea, Puffinus gravis, P. griseus, Catharacta antarctica, Sterna vittata and Anous stolidus. Tristan is the only known breeding site within the group for Pterodroma incerta and of Puffinus griseus, while numbers of Diomedea chlororhynchos are the highest for any island in the Dependency. Pterodroma brevirostris and Puffinus assimilis may also breed. Pterodroma macroptera, P. incerta and Procellaria cinerea have not been proven to breed elsewhere in the Tristan group, possibly because they are winter breeders. There are currently an estimated 40,000 breeding pairs of seabirds, most known from the south-eastern quadrant, which has suffered least from human disturbance. The estimated breeding density is only 500 pairs per km². The terrestrial species include the restricted-range Gallinula comeri, introduced from Gough Island (SH008) in 1956 (3,000 pairs, 1993 estimate), and Nesocichla e. eremita, confined to this island and numbering 40–60 pairs in 1974.There are more records of non-breeding visitors and vagrants on Tristan than from the other islands of the group. This is probably due to the island’s larger size and permanent human presence. Also, due to persecution, there are fewer Catharacta to prey upon them as they arrive. Most records are from the settlement area. Seabirds include Diomedea exulans, D. melanophris, Macronectes giganteus, M. halli, Fulmarus glacialoides, Daption capense, Procellaria a. aequinoctialis, P. a. conspicillata, Puffinus gravis, Oceanites oceanicus, Pelagodroma marina and Larus dominicanus. Shorebirds and landbirds include Casmerodius albus, Egretta thula, Bubulcus ibis, Porphyrula martinica, Calidris fuscicollis and Hirundo rustica. The strong westerlies create favourable conditions for a crossing from South America, and this would explain the presence of gallinules and other non-breeding landbirds that have reached Tristan from that continent. The site requires much further field study, especially the southern side.
Non-bird biodiversity: There are no endemic mammals. The only breeding native mammal is the fur seal Arctocephalus tropicalis, of which there is a small colony at Cave Point on the southern side of the island. Elephant seals Mirounga leonina haul out regularly on Tristan beaches and breed sporadically. Eubalaena glacialis (EN) occurs in offshore waters between September and November, but in very low numbers. Of 62 native terrestrial invertebrates recorded, only four are endemic.
BirdLife International (2019) Important Bird Areas factsheet: Tristan Island. Downloaded from http://www.birdlife.org on 18/04/2019.