Data Zone
Justification of Red List category
Population justification
The population was previously estimated at 250 individuals, with a breeding population of approximately 100 pairs (Ortmann 2013). Surveys in September 2020 recorded only 7 pairs, and estimated a total of 20 remaining pairs. A follow-up survey in January 2021 confirmed that there were approximately 20 adult pairs, and juveniles were also observed. (T. Glass pers. comm. as per A. Schofield, T. Glass, A. Atkinson & M. Davies in litt. 2021). During the surveys in 2021, not all potential territories were visited, and so the true population size may be slightly higher than this estimate (A. Schofield, T. Glass, A. Atkinson & M. Davies in litt. 2021). It is therefore placed here in the band 1-49 mature individuals.
Trend justification
Overall, the population is inferred to be declining due to continuing habitat loss and degradation as a result of infestations of invasive scale insects on their specialist food plant (A. Schofield, T. Glass, A. Atkinson & M. Davies in litt. 2021).
Prior to 2019, the population was estimated to be increasing. Surveys in 1999 estimated there to be 50 pairs (A. Schofield, T. Glass, A. Atkinson & M. Davies in litt. 2021). In 2013, the population was estimated to be at least 75 pairs (Ortmann 2013), while in 2018, there was an estimated 119 pairs (Dilley 2018). Following a population crash due to severe habitat destruction and degradation, the population was estimated to be c.20 pairs in surveys conducted in 2020 and 2021 (A. Schofield, T. Glass, A. Atkinson & M. Davies in litt. 2021).
This species lost 70% of its woodland habitat in storms in 2019, and the remaining Phylica woodland is becoming increasingly infested with invasive scale insects, Hemiberlesia rapax, and Coccus hesperidum and its associated sooty mould, Seiridium phylicae (Dilley et al. 2020; A. Schofield, T. Glass, A. Atkinson & M. Davies in litt. 2021). This species is dependent on the Phylica trees for food. H. rapax has spread to almost all Phylica trees on Nightingale, and it is thought to be inevitable that the juvenile C. hesperidum found on the island will colonise Phylica throughout the island (A. Schofield, T. Glass, A. Atkinson & M. Davies in litt. 2021). In heavily infested woodlands on Inaccessible Island, another Phylica specialist, Dunn's Finch (Nesospiza acunhae dunnei) has exhibited large declines, with male Dunn's finches declining by 50% over the last 10 years. If this situation replicates on Nightingale Island, then it is suspected that Wilkins's Finch will exhibit similar declines in the future, placed here in the band 50-60% over three generations.
Nesospiza wilkinsi is restricted to Nightingale Island, Tristan da Cunha (St Helena to UK), in the South Atlantic Ocean (Ryan 2008).
It is largely restricted to areas which support some Phylica arborea trees, but also regularly occurs in tussock-grassland. The breeding season is from late October to February, with nests located in clumps of vegetation near ground-level.
Visits to Nightingale are made fairly regularly by islanders and researchers using small vessels based at Tristan, and the fishing vessels that operate in Tristan waters (A. Bond in litt. 2016). This species is thus permanently at risk from the accidental introduction of mammalian predators which could prey on eggs, chicks and nesting birds. Another threat is the invasion of the introduced New Zealand flax Phormium tenax into areas of Phylica, but initial clearing in 2004 and ongoing follow-up operations have largely eliminated this threat (P. G. Ryan in litt. 2012). It may be benefiting from the cessation of wood cutting by Tristan islanders visiting Nightingale, resulting in some Phylica regeneration.
However, alien scale insects Hemiberlesia rapax (common on Tristan and locally common on Inaccessible) are also on Nightingale. Though they do not appear to have significant impacts on Phylica fruit production, no Phylica tree measured on Nightingale had a basal diameter > 20 cm, suggesting some impact (Ortmann 2013). Another threat is a black sooty mould fungus Seiridium phylicae which was previously introduced from Tristan to Inaccessible, and was found to have colonised Nightingale in 2016 (A. Schofield, T. Glass, A. Atkinson & M. Davies in litt. 2021). The scale insect associated with this sooty mould, Coccus hesperidum, was also found on the island in 2017, and juveniles are believed to be widespread on Nightingale. Evidence from Inaccessible Island demonstrates that C. hesperidum markedly reduces fruit loads of Phylica trees, and causes the death of large mature trees (Dilley et al. 2020; A. Schofield, T. Glass, A. Atkinson & M. Davies in litt. 2021).
It is also threatened by catastrophic weather events and the effects of climate change: strong winds blow down large swathes of Phylica (as happened in 2001 [P. G. Ryan in litt. 2012] and in 2019/2020 when it lost 70% of its habitat [A. Schofield, T. Glass, A. Atkinson & M. Davies in litt. 2021]).
Conservation Actions Underway
Current efforts are focusing on restoring Phylica woodlands on Nightingale, and understanding drivers of Wilkins’ Bunting population dynamics. Phylica tree propagation is underway in a project run by Tristan Government. Phylica has now been successfully propagated, however it is very slow growing and so this is a long-term solution (A. Schofield, T. Glass, A. Atkinson & M. Davies in litt. 2021). The use of a biological agent to control C. hesperidum infestations is now being actioned. Funding has been secured from Darwin Plus for the parasitoid Miroterys nietneri to be sent to Tristan in January. After after six weeks of rearing and building the population, it will be released at the beginning of March, and again in spring (A. Schofield, T. Glass, A. Atkinson & M. Davies in litt. 2021).
18 cm. Large-billed, island bunting. Uniform olive-green above with yellowish-green underparts which show streaking on belly and flanks. Yellow face and throat with prominent, short, yellow eyebrow-stripe. Similar spp. Superficially resembles Tristan Bunting N. acunhae but differs chiefly in having unusually disproportionate, massive bill, also paler yellow underparts with streaking on flanks and belly.
Text account compilers
Clark, J.
Contributors
Atkinson, A., Calvert, R., Davies, M., Glass, T., Ryan, P.G., Schofield, A. & Symes, A.
Recommended citation
BirdLife International (2024) Species factsheet: Wilkins's Finch Nesospiza wilkinsi. Downloaded from
https://datazone.birdlife.org/species/factsheet/wilkinss-finch-nesospiza-wilkinsi on 22/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 22/12/2024.