Justification of Red List category
Although this species is abundant within its extremely small range and is not currently thought to be declining, the potential arrival of invasive species on Inaccessible Island could lead to extremely rapid declines such that the species could become Critically Endangered or Extinct within a short time period (as has happened on Tristan da Cunha). It is consequently classified as Vulnerable.
The species is abundant on Inaccessible Island, especially in coastal tussock, with the total population estimated at 23,400 mature individuals comprising three distinctive colour morphs and a large number of 'hybrids' between these morphs (Ryan 2008).
The species's population is suspected to be stable owing to the absence of any serious and immediate threats.
Nesospiza acunhae occurs on Inaccessible Island, Tristan da Cunha (St Helena to UK) in the South Atlantic Ocean (Ryan 2008). It became extinct on the main island of Tristan da Cunha before the end of the 19th century (Fraser and Briggs 1992). It is abundant, especially on coastal tussock (Ryan 2008).
On Inaccessible, the upland small-billed form N. a. fraseri occurs primarily in fern-bush and wet heath between 300-600 m and has a brighter yellow/green coloration than the lowland small-billed form N. a. acunhae, which is found mainly in tussock-grassland on the coastal slopes (Ryan 2008). It is probable that the variation in plumage between the forms is due to dietary differences (Ryan et al. 1994), with 'bright' birds feeding more extensively on carotenoid-rich fruits of Nertera than 'dull' ones, which feed predominantly on flowers and seedheads of Spartina species. The large-billed form N. a. dunnei is closely associated with Phylica copses (Ryan et al. 2008).
This species is permanently at risk from the accidental introduction of mammalian predators which could prey on eggs, chicks and nesting birds. Mice and rats are present on the nearby inhabited island of Tristan da Cunha, and as illustrated by the shipwreck of the Oliva in 2011, even the world's remotest places are not immune from the risk of marine accident (Guggenheim and Glass 2014). Another threat is the invasion of the introduced New Zealand flax Phormium tenax into areas of Phylica (P. G. Ryan in litt. 1999) resulting in the possible degradation of its habitat; control measures started in 2004 have reduced this risk, but plants remain established on the island. The large-billed coastal form N. a. dunnei could be threatened by reduced fruit loads on Phylica trees infested by an introduced scale insect and associated sooty moulds (Ryan et al. 2014).
Conservation Actions Underway
Inaccessible is a nature reserve and UNESCO World Heritage Site. Although Tristan Islanders retain the right to collect driftwood and guano, other access is restricted (Cooper et. al. 1995). A management plan for the island was published in 2001, and updated in 2010 (Ryan and Glass 2001, RSPB and TCD 2010); this is being updated again in 2016. Inaccessible was added to the Gough Island World Heritage Site in 2004 (RSPB and TCD 2010). New Zealand flax has been removed from coastal and plateau areas and is now confined to c.300 m of cliffs around the Waterfall (P. G. Ryan in litt. 2012).
Text account compilers
Calvert, R., Symes, A. & Stringer, C.
Cooper, J., Ryan, P.G. & Bond, A.
BirdLife International (2023) Species factsheet: Nesospiza acunhae. Downloaded from http://datazone.birdlife.org/species/factsheet/inaccessible-island-finch-nesospiza-acunhae on 11/12/2023.
Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from http://datazone.birdlife.org on 11/12/2023.