Justification of Red List Category
There are no confirmed recent records of the species, but at least two unconfirmed records have been reported since 2000 implying that the species may yet still persist in very small numbers. Following the application of new methods for estimating the probability of a species remaining extant, the species is now considered to be extant, although it must have an extremely small population, hence it is listed as Critically Endangered.
The lack of any confirmed recent reports suggests that the population size is likely very low (probably less than 50 mature individuals).
There is no evidence to indicate that the species's area of habitat is declining, but the lack of recent confirmed records and lack of knowledge about the reasons for the species's past decline prevent an assessment of the current population trend.
Acrocephalus longirostris is restricted to the island of Moorea in the Society Islands, French Polynesia. It was recorded as being rare by the Whitney South Sea Expedition in 1921 (Thibault and Cibois 2017). Two individuals were recorded in Oponohu land in 1971-73 and the last confirmed record of the species was in a bamboo grove in Atiha Valley in 1981 (Thibault and Cibois 2017). There have been unconfirmed reports from the mid-1990s, 2000s and in 2010 (A. Gouni in litt. 2007, Cibois et al. 2008, A. Gouni in litt. 2011). There were searches for the species in 1986-1987, and also some untargeted survey work in 2008. The species was formerly considered to be possibly extinct, but the probability of it being extant has been estimated at 0.894 based on records and surveys, and 0.218 based on threats (Butchart et al. 2018) and therefore the species is now considered to be extant, albeit extremely rare.
It occurs in bamboo thickets and second growth forests in river valleys and hillsides to 1,700 m. It feeds on insects but also takes lizards, small fish, crayfish, snails and nectar (Pratt et al. 1987, Thibault 1988). It is thought to breed exclusively in bamboo thickets (P. Raust in litt. 2007).
The causes of the species's decline are unknown (Thibault and Cibois 2017). The development of hydro-electricity opened up the interior of the island with new roads and tracks (P. Raust in litt. 2007), leading to a considerable increase in the exploitation of bamboo as well as invasion by the neotropical weed Miconia and an increase in tourists in four-wheel drive vehicles. These factors have modified the habitat considerably and have caused a loss of breeding habitat, as well as causing disturbance (P. Raust in litt. 1999, 2007). The introduction of feral cats Felis catus, rats Rattus spp. (A. Gouni in litt. 2012) and many alien bird species, including the aggressive Common Myna Acridotheres tristis, may also contribute to its rarity (Thibault 1988, Seitre and Seitre 1991).
Conservation Actions Underway
No targeted actions are known.
Text account compilers
Wheatley, H., Shutes, S., Khwaja, N., Stattersfield, A., Mahood, S., Martin, R., O'Brien, M., Derhé, M.
Blainvillain, C., Gouni, A. & Raust, P.
BirdLife International (2020) Species factsheet: Acrocephalus longirostris. Downloaded from http://www.birdlife.org on 21/01/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 21/01/2020.