This discussion was first published as part of the 2017 Red List update. At the time a decision regarding the status of several species was pended, but to enable potential reassessment of these species as part of the 2019 Red List update this post remains open and the date of posting has been updated.
The species which are still open for discussion are; White-winged Nightjar (Eleothreptus candicans), Black-breasted Puffleg (Eriocnemis nigrivestis), Yellow-shouldered Amazon (Amazona barbadensis), Flores Hanging-Parrot (Loriculus flosculus), Slaty Becard (Pachyramphus spodiurus), Foothill Elaenia (Myiopagis olallai), Monteiro’s Bush-shrike (Malaconotus monteiri), Choco Vireo (Vireo masteri), Turner’s Eremomela (Eremomela turneri), Bicol Ground-warbler (Robsonius sorsogonensis), Vietnamese Cutia (Cutia legalleni), Multicolored Tanager (Chlorochrysa nitidissima), Azure-rumped Tanager (Tangara cabanisi).
IUCN define the Extent of Occurrence (EOO) of a species as “the area contained within the shortest continuous imaginary boundary which can be drawn to encompass all the known, inferred or projected sites of present occurrence of a taxon, excluding cases of vagrancy” (IUCN 2001, 2012). The EOO effectively measures the spatial spread of areas currently known to be occupied by a species. This is important for species conservation as areas that are closer together are likely to experience more similar environmental conditions and processes. These processes include natural and anthropogenic threats to a species, and so areas closer together are more likely to suffer from the same threatening events. This could therefore lead to higher extinction risk for species that are spread over a small are compared to those spread over a larger area (see IUCN Standards and Petitions Subcommittee 2017).
This is taken into account when conducting Red List assessments, when assessing a species against criterion B1. To qualify as Threatened under this criterion, a threshold EOO value must be met (Critically Endangered: <100km2; Endangered: <5,000km2; Vulnerable: <20,000km2), along with at least 2 other conditions (see IUCN 2001, 2012).
It has been decided that the most appropriate way to calculate the EOO of a species is using Minimum Convex Polygons (IUCN 2001, 2012, Joppa et al. 2016). These are defined as “the smallest polygon in which no internal angle exceeds 180 degrees and which contains all the sites of occurrence” (IUCN 2001, 2012). For species occurring in several discrete patches, this would still take the form of one continuous area, rather than separate polygons as such disjunctions are ‘strongly discouraged’ by IUCN (IUCN Petitions and Standards Subcommittee 2017). This is because using separate, discrete polygons would not accurately reflect how a large range size reduces the global impact on a species from local processes. In the case where species may be found in only a very limited number of very small, discrete areas, the most appropriate parameter to use would be Area of Occupancy (AOO), which a species is assessed against under criterion B2.
Since Minimum Convex Polygons have been adopted by IUCN as the method to calculate, BirdLife has gone through the process of re-calculating all of the EOO values for bird species using this methodology. This has had the consequence that several species currently listed under criterion B1 would no longer have an EOO that meets the threshold for the Red List Category they are currently listed under. Unless the species trigger other criteria at the threshold for their current Red List Category, this means that they would warrant downlisting.
These species, and their proposed new Red List statuses are presented here.
IUCN. 2001. IUCN Red List Categories and Criteria: Version 3.1. IUCN Species Survival Commission. IUCN, Gland, Switzerland and Cambridge, U.K.
IUCN. 2012. IUCN Red List Categories and Criteria: Version 3.1. Second edition. IUCN Species Survival Commission. IUCN, Gland, Switzerland and Cambridge, U.K. Available at: www.iucnredlist.org/technical-documents/categories-and-criteria.
IUCN Standards and Petitions Subcommittee. 2017. Guidelines for Using the IUCN Red List Categories and Criteria. Version 13. Prepared by the Standards and Petitions Subcommittee. Downloadable from http://www.iucnredlist.org/documents/RedListGuidelines.pdf.
Joppa, L. N.; Butchart, S. H. M.; Hoffmann, M.; Bachman, S. P.; Akçakaya, H. R.; Moat, J. F.; Böhm, M.; Holland, R. A.; Newton, A.; Polidoro, B.; Hughes, A. 2016. Impact of alternative metrics on estimates of extent of occurrence for extinction risk assessment. Conservation Biology 30: 362-370.