Rimatara is a raised island in the Austral (or Tubuai) Islands and is the second smallest of all EBAs after Laysan (EBA 216). Other islands in the Austral group include Maria, Rurutu, Tubuai, Raivavae, and, c.300 km to the south-east, Rapa (treated as Secondary Area s136) and Marotiri. All of these islands are politically part of French Polynesia, which is a French overseas territory (see also EBAs 212-214, and Secondary Area s136).

On Rimatara, the centre of the island consists of a once-forested weathered volcanic hill surrounded by a discontinuous ring of swamplands. The raised coral platform ('makatea') forms a coastal rampart around the north-western half of the island and is covered with forest and scrublands, with the south-eastern half being an extensive coastal plain.

As a result of the recent recognition of the specific status of Acrocephalus rimatarae (formerly regarded as a race of A. vaughani by Sibley and Monroe 1990, but treated as a species by Graves 1992 and Sibley and Monroe 1993; see EBA 215 and Secondary Area s137), Rimatara, now with two endemic restricted-range species, qualifies as an EBA.

Vini kuhlii, the second restricted-range species occurring in this EBA, is also present on islands in Kiribati (Secondary Area s134), to which it appears to have been introduced, and it is speculated by Steadman (1991) that the species was spread widely through the Southern Cook Islands prior to 1800 but was extirpated through exploitation by Polynesian settlers.

In general, the Austral Islands are poorly known, and Maria and Marotiri have never been properly investigated by an ornithologist. An unidentified Acrocephalus was reported from Raivavae in 1968, but was not found in 1990 (Seitre and Seitre 1991), and could therefore have been a vagrant.

Today the coastal plains of Rimatara are typically covered in coconut plantations and the upper volcanic slopes with fernlands, grasslands and introduced forestry, while the lower slopes form a horticultural belt which is extensively planted with recently introduced food plants.

This habitat alteration does not, however, appear to be a major threat to the two endemic species. In 1989 Acrocephalus rimatarae was found to be common (although no estimate of population was made) and widespread, particularly at lower elevations (Seitre and Seitre 1991). In 1992 Vini kuhlii was considered to be common in the belt of mixed horticultural woodland, though less common in the central hills and coastal plains and rare in the extensive makatea forest and scrub (with a total population on Rimatara of c.905 birds) (McCormack and Künzlé 1996).

The effects of introduced species could, however, be serious, given the tiny ranges of both species; although Acrocephalus rimatarae was not evaluated for threatened status by Collar et al. (1994), it would certainly qualify as Vulnerable on the basis of its range size. A preliminary rat survey revealed the presence of both Pacific rat Rattus exulans and brown rat R. norvegicus, but not of black rat R. rattus his latter the most agile tree-climber of the three species of rat in Polynesia, being widely associated with the decline of birds on oceanic islands (Atkinson 1985, Seitre and Seitre 1991), and its absence is perhaps the main reason why Vini kuhlii is still relatively abundant on Rimatara. The highest conservation priority should therefore be given to confirming the absence of R. rattus on Rimatara and the implementation of a major quarantine programme to ensure that it is not accidentally introduced; reintroduction of Vini kuhlii to islands within its former natural range is also recommended (McCormack and Künzlé 1996).

Recommended citation
BirdLife International (2024) Endemic Bird Area factsheet: Rimatara. Downloaded from https://datazone.birdlife.org/eba/factsheet/218 on 23/11/2024.