5 thoughts on “Bougainville Island-thrush (Turdus bougainvillei)”
Many thanks to everyone who has contributed to this discussion. We greatly appreciate the time and effort invested in commenting. The window for consultation is now closed and we are unable to accept any more comments until 2 February 2026. We will now analyse and interpret the information, and we will post a preliminary decision on this species’ Red List category on this page on 2 February 2026, when discussions will re-open.
We have received the following comment from Guy Dutson via email:
(1) I described this taxon as ‘fairly common’ in Dutson (2011) based on Hadden (2004) but more recent records in the Emperor Range (eBird, Woxvold & Novera 2021 and Schmidt 2024), and the Crown Prince range (eBird, J. Bergmark pers. comm.) indicate that it is uncommon, with most observers recording one or two individuals less than daily in suitable habitat. For example, Schmidt recorded two individuals once in 6 km of surveys between 1300‒2463 m on Mt Balbi. Mittermeier, Dutson & Cottee-Jones (https://ebird.org/tripreport/279655) had 12 individuals (including duplicates on different days) in 55 hours or 36 km of surveys between 1300‒1900 m at Kunua in 2024. Using the same assumptions as Island-Thrushes on Kolombangara, i.e. an effective detection distance of 10 m either side of the trail, suggests a population density of 14/42/0.02 = about 17 birds / km2. BirdLife could measure the area above 1400 m to estimate the total population size (although I recorded it down to 1200 m in Dutson 2011, it is rare below 1400 m).
(2) there is negligible anthropogenic forest degradation or clearance above 1400 m but, especially in the Crown Prince Range, bird densities are low and the species is likely to be hunted by the small number of people living in the mountains – although there might be a very slow ongoing decline, it would not plausibly meet 10% / 3 generations
(3) I’m not convinced about listing it as Near Threatened under B as I can’t imagine it ever coming close to meeting the criteria (a) or (c); however, I can support it being Near Threatened under C1.
(4) I note that the proposed B1(iii) + 2b(iii) is consistent with Bougainville Thrush Zoothera atrigena which I also think is more likely to approach C1
I also note that both of these are inconsistent with the listing of Bougainville Bush-warbler Horornis haddeni = Near Threatened under criteria B1ab(iii,v)+2ab(iii,v); C2a(i). Note that H haddeni occurs at lower altitudes where it is exposed to slow rates of anthropogenic forest loss.
We thank G. Dutson for their helpful comment above. Based on this, there is no longer considered to be a continuing decline in habitat area, extent or quality for this species, and the assessment will be updated accordingly. The population density of 17 birds/km2 yields a population size of c. 6,000, meeting the population size threshold for Criterion C. Although the population trend has not been directly quantified, a slow decline is now suspected based on the information provided above. Given the possibility that all individuals belong to a single subpopulation, the species is considered to approach thresholds under C2a(ii).
Based on available information therefore, our preliminary proposal for the 2026 Red List would be to list Bougainville Island-thrush as Near Threatened under Criterion C2a(ii). There is now a period for further comments until the final deadline on 8 February 2026, after which the recommended categorisations will be put forward to IUCN.
The final 2026 Red List categories will be published on the BirdLife and IUCN websites later this year, following further checking of information relevant to the assessments by both BirdLife and IUCN.
Many thanks to everyone who has contributed to this discussion. We greatly appreciate the time and effort invested in commenting. The window for consultation is now closed and we are unable to accept any more comments. We will analyse and interpret the information, and a final decision on this species’ Red List category will be posted on this page on 16 February 2026.
Recommended categorisation to be put forward to IUCN
The final categorisation for this species has not changed. Bougainville Island-thrush is recommended to be listed as Near Threatened, approaching thresholds under Criterion C2a(ii).
Many thanks to everyone who contributed to the 2026.1 GTB Forum process. The final Red List categories will be published on the BirdLife and IUCN websites later this year, following further checking of information relevant to the assessments by both BirdLife and IUCN.
Many thanks to everyone who has contributed to this discussion. We greatly appreciate the time and effort invested in commenting. The window for consultation is now closed and we are unable to accept any more comments until 2 February 2026. We will now analyse and interpret the information, and we will post a preliminary decision on this species’ Red List category on this page on 2 February 2026, when discussions will re-open.
We have received the following comment from Guy Dutson via email:
(1) I described this taxon as ‘fairly common’ in Dutson (2011) based on Hadden (2004) but more recent records in the Emperor Range (eBird, Woxvold & Novera 2021 and Schmidt 2024), and the Crown Prince range (eBird, J. Bergmark pers. comm.) indicate that it is uncommon, with most observers recording one or two individuals less than daily in suitable habitat. For example, Schmidt recorded two individuals once in 6 km of surveys between 1300‒2463 m on Mt Balbi. Mittermeier, Dutson & Cottee-Jones (https://ebird.org/tripreport/279655) had 12 individuals (including duplicates on different days) in 55 hours or 36 km of surveys between 1300‒1900 m at Kunua in 2024. Using the same assumptions as Island-Thrushes on Kolombangara, i.e. an effective detection distance of 10 m either side of the trail, suggests a population density of 14/42/0.02 = about 17 birds / km2. BirdLife could measure the area above 1400 m to estimate the total population size (although I recorded it down to 1200 m in Dutson 2011, it is rare below 1400 m).
(2) there is negligible anthropogenic forest degradation or clearance above 1400 m but, especially in the Crown Prince Range, bird densities are low and the species is likely to be hunted by the small number of people living in the mountains – although there might be a very slow ongoing decline, it would not plausibly meet 10% / 3 generations
(3) I’m not convinced about listing it as Near Threatened under B as I can’t imagine it ever coming close to meeting the criteria (a) or (c); however, I can support it being Near Threatened under C1.
(4) I note that the proposed B1(iii) + 2b(iii) is consistent with Bougainville Thrush Zoothera atrigena which I also think is more likely to approach C1
I also note that both of these are inconsistent with the listing of Bougainville Bush-warbler Horornis haddeni = Near Threatened under criteria B1ab(iii,v)+2ab(iii,v); C2a(i). Note that H haddeni occurs at lower altitudes where it is exposed to slow rates of anthropogenic forest loss.
Preliminary proposal
We thank G. Dutson for their helpful comment above. Based on this, there is no longer considered to be a continuing decline in habitat area, extent or quality for this species, and the assessment will be updated accordingly. The population density of 17 birds/km2 yields a population size of c. 6,000, meeting the population size threshold for Criterion C. Although the population trend has not been directly quantified, a slow decline is now suspected based on the information provided above. Given the possibility that all individuals belong to a single subpopulation, the species is considered to approach thresholds under C2a(ii).
Based on available information therefore, our preliminary proposal for the 2026 Red List would be to list Bougainville Island-thrush as Near Threatened under Criterion C2a(ii). There is now a period for further comments until the final deadline on 8 February 2026, after which the recommended categorisations will be put forward to IUCN.
The final 2026 Red List categories will be published on the BirdLife and IUCN websites later this year, following further checking of information relevant to the assessments by both BirdLife and IUCN.
Many thanks to everyone who has contributed to this discussion. We greatly appreciate the time and effort invested in commenting. The window for consultation is now closed and we are unable to accept any more comments. We will analyse and interpret the information, and a final decision on this species’ Red List category will be posted on this page on 16 February 2026.
Recommended categorisation to be put forward to IUCN
The final categorisation for this species has not changed. Bougainville Island-thrush is recommended to be listed as Near Threatened, approaching thresholds under Criterion C2a(ii).
Many thanks to everyone who contributed to the 2026.1 GTB Forum process. The final Red List categories will be published on the BirdLife and IUCN websites later this year, following further checking of information relevant to the assessments by both BirdLife and IUCN.