The 10 high volcanic islands and five coral atolls comprising the Society Islands can be divided into two main groups, each named after its position relative to the dominant south-east trade winds: the Leeward Islands in the north-west and the Windward Islands in the south-east. The archipelago is a part of French Polynesia, an overseas territory of France (see also EBAs 211, 212, 214, and Secondary Area s136). With a land area of 1,045 km² Tahiti is by far the largest of the islands, and it rises to 2,241 m at Mt Marau.

The native vegetation consists of strand forest with Cocos and Pandanus, lowland dry forest and extensive montane rain forest with cloud forest on the peaks (Davis et al. 1986).

All the restricted-range birds are forest species, though many occur in secondary habitats and plantations. Five species are restricted to one or two islands but were once more widely distributed. Tahiti supports seven restricted-range species (including three single-islands endemics), while the other islands now have only one or two.

As well as the two extinct endemic species listed in the 'Status and habitat' table, an additional three endemics were collected or seen on Cook's voyage in 1773: Tahiti Rail Gallirallus pacificus (Tahiti only), Tahitian Sandpiper Prosobonia leucoptera (Moorea and Tahiti) and Raiatea Parakeet Cyanoramphus ulietanus (Raiatea only).

The Society Islands are perhaps among the most devastated island groups in the whole of the Pacific (Hay 1986). The lowland forest has been greatly modified and all the low atolls have been largely converted to coconut plantations (Davis et al. 1986).

Over the last 30 years there has been much habitat modification on Tahiti in particular, with the invasion of an introduced aggressive Neotropical tree Miconia calvescens contributing to the progressive disappearance of local trees. It is likely that the replacement of remaining primary forest by this pest (which forms monospecific stands and now dominates forest over 65% of the island) has contributed to the recent decline of Pomarea nigra on Mt Marau; this species has apparently been rare throughout the twentieth century but was noted from only four valleys out of 39 visited in 1986-1991 (Monnet et al. 1993, Meyer 1996).

The greatest overall threat, however, appears to have come from introduced species, both birds (more than half of the Tahitian avifauna is non-native) and mammals, and it is likely that past extinctions can be linked at least in part to the effects of these introductions. For example, Common Myna Acridotheres tristis, one introduced bird pest, is thought to predate the eggs and young of Collocalia leucophaeus and may compete for food with Acrocephalus caffer (Holyoak and Thibault 1984, Seitre and Seitre 1991, 1992).

The species which has suffered the greatest recent range reduction is Vini peruviana; its extirpation from many islands correlates very well with the spread of the introduced Swamp Harrier Circus approximans (Holyoak and Thibault 1984), and has also been linked to the arrival of black rat Rattus rattus, while its recent decline on Manuae is possibly explained by the release of cats there (Seitre and Seitre 1991, 1992).

Thibault (1988) identified the following areas as priorities for native landbird conservation: Mt Marau on Tahiti (for Pomarea nigra in particular); vallée de Vaiote on Tahiti; the island of Manuae; the wooded vallée d'Avera on Raiatea; and the lowland humid forest of Oponohu on Moorea. In 1990 the Valley of Fa'aiti Natural Park on Tahiti was established, and a study of Manuae has been proposed to classify the island as a reserve (Drollet 1990), and to explore the feasibility of cat and rat eradication.

Recommended citation
BirdLife International (2024) Endemic Bird Area factsheet: Society Islands. Downloaded from https://datazone.birdlife.org/eba/factsheet/214 on 23/11/2024.