Is EOO the appropriate measure of habitat extent for this species as its range is so disjunct and generally restricted to higher elevation forest? Would not AOO be better and can this not be estimated / inferred from BirdLife or other data? This would support a more helpful analysis of threat status.
Many thanks to everyone who has contributed to this discussion. We greatly appreciate the time and effort invested by so many people in commenting. The window for consultation is now closed. We will analyse and interpret the new information and post a preliminary decision on this species’s Red List status on this page in early July.
Thank you once again,
BirdLife Red List Team
Based on available information, our preliminary proposal for the 2021 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 in mid-July, after which the recommended categorisations will be put forward to IUCN.
The final 2021 Red List categories will be published on the BirdLife and IUCN websites in December 2021, following further checking of information relevant to the assessments by both BirdLife and IUCN.
Please see my previous comment. EOO does not seem to be the relevant measure of distribution.
If this species were to meet Criterion B2 and (a – possible as known from six sites) and (b – Met), then it could be listed as Vulnerable.
Note that you state it meets the threshold for B2(b)(ii) but not B2(b)(i), so you may want to be consistent and update this so that you are either working with EOO or AOO.
Recommended categorisation to be put forward to IUCN
The final categorisation for this species has not changed. Crossley’s Ground-thrush is recommended to be listed as Least Concern.
The extent of occurrence (EOO) is a parameter that measures the spatial spread of the areas currently occupied by the species. It is not intended to be an estimate of the amount of occupied or potential habitat, or a general measure of the species’s range.
The area of occurrence (AOO) for this species, when calculated sensu IUCN by applying a 2 km x 2 km square grid over the current range map, is 56,300 km2. This is much greater than the threshold of <2,000 km2, and therefore this species does not qualify for listing as threatened under Criterion B2.
A ‘location’, as defined by IUCN, is not the number of sites in which a species is found, but a geographically or ecologically distinct area in which a single threat can rapidly affect all individuals in a short space of time. Furthermore, the main threat to this species is forest loss. Based on the low rate of forest loss in its range, it is not likely to rapidly affect all individuals within a single generation or three years. Therefore, the number of locations is here considered to be much higher than the threshold of 10 locations, and as such this species does not meet subcriterion a (locations).
When a species has specific habitat requirements, and a particular threat is known to be reducing or degrading that habitat, then it is possible to infer a continuing decline in AOO, even when the AOO does not meet the initial threatened threshold. In this case, the species has a high forest dependency, and is experiencing ongoing forest loss and degradation. Therefore, a continuing decline in AOO is inferred under subcriterion b(ii).
Conversely, we do not yet have evidence, or reason to infer that the forest loss is reducing the spatial spread of the species across its range, and therefore a continuing decline in EOO has not been inferred under subcriterion b(i).
Many thanks for everyone who contributed to the 2021 GTB Forum process. The final 2021 Red List categories will be published on the BirdLife and IUCN websites in December 2021, following further checking of information relevant to the assessments by both BirdLife and IUCN.
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Contact the BirdLife Red List Team under redlistteam [at] birdlife [dot] org.