Archived 2017 topics: Rimatara Reed-warbler (Acrocephalus rimitarae): uplist to Critically Endangered?

BirdLife species factsheet for Rimatara Reed-warbler:


Rimatara Reed-warbler, Acrocephalus rimitarae, is endemic to the small island of Rimatara in the Austral Islands of French Polynesia, with a Minimum Convex Polygon Extent of Occurrence of only 10km2. The species occurs across the island, even in swamps and the central fern-covered hills (Thibault and Cibois 2006a,b). However, it may be dependent of wooded areas for at least part of the year as breeding predominantly occurs in forested areas as well as the undergrowth of coconut groves and mixed horticulture (Thibault and Cibois 2006a,b).

The fact that it may be dependent on such habitat for breeding may leave it vulnerable to habitat destruction. The construction of an airport destroyed over a third of native forest (Thibault and Cibois 2006a), and it was extended in 2015 (Blanvillain et al. 2015), although (after the initial build at least) suitable habitat remained (J. Millet in litt. 2007). A threat that encompasses the whole of the range of this species is from invasives. Feral cats have become increasingly common on the islands according to local people (G. Dutson in litt. 2016) and they are likely to cause some mortality to this species (Thibault and Cibois 2006a,b). Polynesian and Brown Rats (Rattus exulans and R. norvegicus respectively) are both present on the island too. The Common Myna, Acridotheres tristis, and Black Rat, R. rattus, are not yet present on the island but their potential introduction remains of high concern given the declines and extinctions these species potentially have been involved with (e.g. Thibault and Cibois 2006a,b), although other Pacific Acrocephalus species do coexist with R. rattus (Seitre and Seitre 1991). Thus, given the threats it may be facing, and the continuing degradation of its habitat, it is considered to be undergoing a slow ongoing decline (C. Blanvillain in litt. 2016 per G. Dutson in litt. 2016).

The species is considered it to be abundant over much of Rimatara (P. Raust in litt. 2012, C. Blanvillain in litt. 2016 per G. Dutson in litt. 2016), with the population having been estimated several times over the years, using a variety of methods. Point count observations in 2002 gave a population estimate of 5,000 birds (Blanvillain 2002). Territory mapping techniques used by Thibault and Cibois (2006a) gave estimates of 1,777-2,567 breeding birds in 2004 (roughly 2,665-3,850 individuals), and transects gave estimates of 740 (Raust and Sanford 2002), 675 (Gouini 2004) and 670 (Albar et al. 2009), though applying a correction to account for differences in methodology would lead to higher estimates from these (Blanvillain et al. 2015). The most recent estimate generated is 971 individuals (Blanvillain et al. 2015). Taking into account corrections (see Blanvillain et al. 2015), the range of estimates fall into the range of approximately 900-3,850 individuals, which roughly equates to 600-2,600 mature individuals (G. Dutson in litt. 2016).

The Rimatara Reed-warbler is currently listed as Vulnerable under criteria D1+2 on the basis of it occurring on just one small island with a potentially small population size (see BirdLife International 2017). This is because the species was tentatively considered to be stable, but expert opinion is that it should now be treated as undergoing a slow decline (C. Blanvillain in litt. 2016 per G. Dutson in litt. 2016). From this species would meet the threshold for Endangered under criterion C2a(ii). However, in the recent regional Red List for France, which included an assessment of the birds of French Polynesia (UICN France 2015), this species was listed as Critically Endangered under criteria B1ab(iii)+2ab(iii). Based on available information, though, our proposal differs from this in two respects. Firstly we do not include criterion B2 because, despite the species likely having a very small Area of Occupancy (AOO), the AOO not been calculated by BirdLife using the strict method required by IUCN (using 2km x 2km grid squares) (see IUCN Standards and Petitions Subcommittee 2016). Secondly, expert opinion is that the species is likely in decline, and so condition (v) under criterion B1b would be met in addition to condition (iii). Therefore, we propose for the species to be listed as Critically Endangered under criterion B1ab(iii,v), on the basis that the species has an extremely small Extent of Occurrence, confined to one very small island, where the population and area/quality of habitat is declining.

We welcome any comments regarding this proposed uplisting.



Albar, G.; Doukas, T.; Kape, J.; Gouni, A. 2009. Programme de conservation du Lori de Kuhl et suivi des effectifs de Rousserolles de Rimatara en 2009. Société d’Ornithologie de Polynésie, Tahiti, Polynésie Française.

BirdLife International. 2017. Species factsheet: Acrocephalus rimitarae. Downloaded from on 31/03/2017.

Blanvillain, C. 2002. Les oiseaux terrestres de Rimatara et des Australes. 2ème phase. Rapport de mission au Service de l’Equipement de Polynésie française et à la SOP. Société d’Ornithologie de Polynésie, Tahiti, Polynésie Française

Blanvillain, C.; Hatitio, G.; Mooroa, T.; Percheron, E.; Sulpice, H.; Brown, F. 2015. Bilan du programme biosécurisation de l’avifaune de Ua huka et de Rimatara 2015. Rapport final. Rapport SOP Manu à la DIREN et au HautCommissariat. Société d’Ornithologie de Polynésie, Tahiti, Polynésie Française.

Gouni, A. 2004. Etude de l’avifaune de Rimatara. 3ème phase. Société d’Ornithologie de Polynésie, Tahiti, Polynésie Française.

IUCN Standards and Petitions Subcommittee. 2016. Guidelines for using the IUCN Red List categories and criteria. Version 12. Prepared by the Standards and Petitions Subcommittee. Downloadable from

Raust, P.; Sanford, G. 2002. Etude de l’avifaune de Rimatara. 1ère phase. Société d’Ornithologie de Polynésie, Tahiti, Polynésie Française.

Seitre, R.; Seitre, J. 1991. Causes de disparition des oiseaux terrestres de Polynésie Française. South Pacific Regional Environment Programme, Nouméa.

Thibault, J-C.; Cibois, A. 2006a. The natural history and conservation of Acrocephalus rimitarae, the endemic reed-warbler of Rimitara Island, Oceania. Bulletin of the British Ornithologists’ Club 126(3): 201-207.

Thibault, J.-C.; Cibois, A. 2006b. Une situation favorable pour le Rupe de Makatea. Te Manu 54: 2-3.

UICN France; MNHN; SOP Manu. 2015. La Liste rouge des espèces menacées en France – Chapitre Oiseaux de Polynésie française. Paris, France.

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5 Responses to Archived 2017 topics: Rimatara Reed-warbler (Acrocephalus rimitarae): uplist to Critically Endangered?

  1. caroline Blanvillain says:

    Habitat destruction have been important in Rimatara since 2006 and the airport construction: 50 % of the natural forest of the island, located in feo areas (up-lifted corail), have been destroyed (about 80 ha) – this represent 10 % of the island. Even if this warbler is very oportunistic in term of habitat, this may have direct repercussion on its number. In addition, we observe an increasing number of feral cats and the destruction of numerous trees for the development of potatoes crops, the prevention of hurrican damages and the coconut forest regeneration in Rimatara those lasts years.

  2. Ghestemme Thomas says:

    I would suggest to uplist the species from VU to EN, regarding the numbers of birds and the likelihood of extinction, then gather new data on evolution and assess in the future if the sp need to be uplisted to CR.

  3. Philippe Raust says:

    I agree that we should follow the conclusions of IUCN France assessment as this speciec is an endemic of French Polynesia (no other population outside of Rimatara.

  4. caroline Blanvillain says:

    I’ve recently surveyed the population and the results (using distance) give a number of 2225 individuals seen or heard (1780-2781) in 2017, whereas Thibault and Cibois (2006a) gave estimates of 1,777-2,567 breeding birds in 2004 (roughly 2,665-3,850 individuals). If we use the ‘traditional method’ (not taking acount distance) used by Raust, Gouni… this estimate decrease to 1526 birds (-45 %) and if unexperimented people count this bird, quite discret, the estimation drop again to -28 % .
    If we look other estimations : Blanvillain 5000 in 2002/point count; Thibault around 3000 in 2006 by mapping and Blanvillain 2200 (total population) by distance, this could indicate a decrease even if variation in methods is not helping us to follow this evolution.

  5. Hannah Wheatley (BirdLife) says:

    Preliminary proposals

    Based on available information, our preliminary proposal for the 2017 Red List would be to adopt the proposed classifications outlined in the initial forum discussion.

    There is now a period for further comments until the final deadline of 4 August, after which the recommended categorisations will be put forward to IUCN.

    Please note that we will then only post final recommended categorisations on forum discussions where these differ from those in the initial proposal.

    The final 2017 Red List categories will be published on the BirdLife and IUCN websites in early December, following further checking of information relevant to the assessments by both BirdLife and IUCN.

Comments are closed.