Re-assessment of Species against Criterion B1: Red List Implications of the use of Minimum Convex Polygons

This discussion was first published as part of the 2017 Red List update. At the time a decision regarding the status of several was pended, but to enable potential reassessment of these species as part of the 2018 Red List update this post remains open and the date of posting has been updated.

The species which are still open for discussion are; Taczanowski’s Tinamou (Nothoprocta taczanowskii), Black Guan (Chamaepetes unicolor), Bearded Guan (Penelope barbata), Rufous-headed Chachalaca (Ortalis erythroptera), Gorgeted Wood-quail (Odontophorus strophium), Harwood’s Francolin (Pternistis harwoodi), Santa Cruz Ground-dove (Alopecoenas sanctaecrucis), White-winged Nightjar (Eleothreptus candicans), Hyacinth Visorbearer (Augastes scutatus), Black-breasted Puffleg (Eriocnemis nigrivestis), Blossomcrown (Anthocephala floriceps), Oaxaca Hummingbird (Eupherusa cyanophrys), Mexican Woodnymph (Thalurania ridgwayi), Hispaniolan Trogon (Temnotrogon roseigaster), Yellow-shouldered Amazon (Amazona barbadensis), Red-fronted Parrotlet (Touit costaricensis), Flores Hanging-Parrot (Loriculus flosculus), Slaty Becard (Pachyramphus spodiurus), Peruvian Plantcutter (Phytotoma raimondii), Foothill Elaenia (Myiopagis olallai), Rufous Flycatcher (Myiarchus semirufus), Allpahuayo Antbird (Percnostola arenarum), Moustached Antpitta (Grallaria alleni), Monteiro’s Bush-shrike (Malaconotus monteiri), Choco Vireo (Vireo masteri), Palm Crow (Corvus palmarum), Turner’s Eremomela (Eremomela turneri), Bicol Ground-warbler (Robsonius sorsogonensis), Black-hooded Laughingthrush (Garrulax milleti), Vietnamese Cutia (Cutia legalleni), Munchique Wood-wren (Henicorhina negreti), Oberländer’s Ground-thrush (Geokichla oberlaenderi), La Selle Thrush (Turdus swalesi), Thyolo Alethe (Chamaetylas choloensis), White-bellied Blue-robin (Myiomela albiventris), White-winged Apalis (Apalis chariessa), Ankober Serin (Crithagra ankoberensis), Hispaniolan Crossbill (Loxia megaplaga), Tanager Finch (Oreothraupis arremonops), Zapata Sparrow (Torreornis inexpectata), Cochabamba Mountain-finch (Poospiza garleppi), 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.

MCP EOO Red List changes


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:

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

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.

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15 Responses to Re-assessment of Species against Criterion B1: Red List Implications of the use of Minimum Convex Polygons

  1. Praveen J says:

    Ranges of some of the endemic birds are well represented in eBird – for e.g. southern India. To enable calculation of MCP using eBird data, the following tool has been developed.

    1/ Data for a species can be directly download from eBird website (For every request, a data download link is given via email). This same file can be fed into this tool to calculate the MCP – which is used for EOO.

    2/ It uses all data in the file – including records vagrancy. Since definition of vagrancy is a bit subjective, elimination of vagrant records, if need be felt, can be done manually in the tab separated file. After removing the rows, the file may be zipped and it will work with this tool.

    3/ Additional records may also be added into this file to supplement eBird data and the same tool can be used.

    4/ This tool also calculates AOO after selecting the size of the square. This would work well for areas where eBird coverage is very dense. It will also work for areas where coverage is patchy to find the lower bound. E.g. if AOO using this tool is greater than 2,000 then denser data will only increase this value and hence can be safely assigned as least concern.

    As a sample, we calculate the MCP using eBird Data for the threatened/near-threatened species of Western Ghats, to obtain the below values

    Black-and-orange Flycatcher Ficedula nigrorufa 55,612 NT
    Nilgiri Pipit Anthus nilghiriensis  23,516 VU
    Broad-tailed Grassbird Schoenicola platyurus 89,077 VU
    Grey-headed Bulbul Pycnonotus priocephalus 1,22,307 NT
    Kerala Laughingthrush Trochalopteron fairbanki 21,068 NT
    (eBird does not yet split them into two)
    Nilgiri Flycatcher Eumyias albicaudatus 53,994 NT
    Black-chinned Laughingthrush Trochalopteron cachinnans 5,746 EN
    (eBird does not yet split them into two)
    Nilgiri Shortwing Brachypteryx major 12,181 EN
    White-bellied Shortwing Brachypteryx albiventris 5,775 EN
    Nilgiri Wood Pigeon Columba elphinstonii 3,14,438 VU

    Amongst the list of birds that can impact status change. Our numbers match the decision taken by BLI for Black-and-orange Flycatcher (NT->LC) and Nilgiri Flycatcher (NT->LC) – though the MCP values are a bit different.
    However, the MCP values of White-bellied Blue Robin (EN-VU) seem to be significantly different from what BLI calculated.

    It would be worthwhile to also consider AOO (B2 criterion) for all these three species before downlisting.

    • Praveen J says:

      Just a side comment,
      If White-bellied Blue Robin (Shortwing) is indeed considered for downlisting (EN->VU), then the same argument holds true for Nilgiri Blue Robin (Shortwing) (MCP = 12,181).

  2. James Westrip (BirdLife) says:

    The New Zealand national status of Red-fronted Parakeet/Red-crowned Parakeet has recently been re-assessed in the Conservation Status of New Zealand birds, 2016 (Robertson et al. 2017). There are differences in the Categories, Criteria and Thresholds for listing between Robertson et al. (2017) and those used when conducting IUCN Red List assessments, and in Robertson et al. (2017) Red-fronted Parakeet/Red-crowned Parakeet was assessed only as the nominate subspecies C. n. novaezelandiae. In Robertson et al. (2017) this subspecies was listed as Nationally At Risk as a Relict taxon under criterion B, which means that this subspecies was assessed to have a population size of >20,000 mature individuals, with the population stable or increasing at >10%, though the species has undergone a documented decline over the past 1,000 years such that it occupies <10% of its former range.

    Robertson, H. A.; Baird, K.; Dowding, J. E.; Elliott, G. P.; Hitchmough, R. A.; Miskelly, C. M.; McArthur, N.; O’Donnell, C. F. J.; Sagar, P. M.; Scofield, R. P.; Taylor, G. A. 2017. Conservation status of New Zealand birds, 2016. New Zealand Threat Classification Series 19. Department of Conservation, Wellington.

  3. James Westrip (BirdLife) says:

    Preliminary proposals

    Based on available information, our preliminary proposal for the 2017 Red List would be to list:

    Taczanowski’s Tinamou as Vulnerable under criterion C2a(i).

    Black Guan as Least Concern.

    Bearded Guan as Least Concern.

    Rufous-headed Chachalaca as Vulnerable under criterion C2a(i).

    Nahan’s Partridge as Vulnerable under criterion B2ab(ii,iii,v).

    Gorgeted Wood-quail as Vulnerable under criterion B2ab(i,ii,iii,v).

    Harwood’s Francolin as Least Concern.

    Santa Cruz Ground-dove as Vulnerable under criteria B2ab(ii,iii,v); D1.

    Bahian Nighthawk as Least Concern.

    White-winged Nightjar as Endangered under criterion C2a(i).

    Hyacinth Visorbearer as Least Concern.

    Colorful Puffleg as Endangered under criterion B2ab(iii,v).

    Black-breasted Puffleg as Endangered under criteria B1ab(i,ii,iii,v)+2ab(i,ii,iii,v).

    Blossomcrown as Vulnerable under criterion C2a(i).

    Oaxaca Hummingbird as Endangered under criterion C2a(ii).

    Verreaux’s Coua as Least Concern.

    Grand Comoro Scops-owl as Endangered under criterion B2ab(i,ii,iii,v).

    Moheli Scops-owl as Endangered under criteria B2ab(i,ii,iii,v); C2a(ii).

    Hispaniolan Trogon as Least Concern.

    Red-fronted Parrotlet as Vulnerable under criterion C2a(ii).

    Red-crowned Parakeet/Red-fronted Parakeet as Least Concern.

    Flores Hanging-parrot as Vulnerable under criterion B2ab(ii,iii,iv,v).

    Peruvian Plantcutter as Vulnerable under criterion C2a(i).

    Foothill Elaenia as Least Concern.

    Maracaibo Tody-tyrant as Least Concern.

    Rufous Flycatcher as Vulnerable under criterion C2a(i).

    Ancient Antwren as Least Concern.

    Moustached Antpitta as Near Treatened under criterion C2a(i).

    Blackish-headed Spinetail as Vulnerable under criteria A2c+3c+4c; C2a(i).

    Red-shouldered Spinetail as Least Concern.

    Gabon Batis as Least Concern.

    Uluguru Bush-shrike as Endangered under criteria B1ab(iii)+2ab(iii).

    McGregor’s Cuckoo-shrike as Least Concern.

    Choco Vireo as Near Threatened under criterion B2ab(i,ii,iii,v).

    Palm Crow as Least Concern.

    Standardwing Bird-of-paradise as Least Concern.

    Aberdare Cisticola as Vulnerable under criteria A2c+3c+4c; B1ab(i,ii,iii,iv,v).

    Cape Verde Swamp-warbler as Vulnerable under criterion B2ab(ii,iii).

    Turner’s Eremomela as Near Threatened under criterion B2ab(i,ii,iii,iv,v).

    Bicol Ground-warbler as Least Concern.

    Pale-throated Wren-babbler as Near Threatened under criterion B2ab(ii,iii,v).

    Black-hooded Laughingthrush as Least Concern.

    Vietnamese Cutia as Least Concern.

    White-throated Mountain-babbler as Vulnerable under criterion B2ab(i,ii,iii,v).

    Oberländer’s Ground-thrush as Near Threatened under criterion C2a(ii).

    La Selle Thrush as Vulnerable under criteria B2ab(i,ii,iii,iv,v); C2a(i).

    Thyolo Alethe as Vulnerable under criteria A2c+3c+4c; B2ab(i,ii,iii,iv,v).

    White-bellied Blue-robin as Vulnerable under criteria B1ab(i,ii,iii,v)+2ab(i,ii,iii,v).

    Black-and-orange Flycatcher as Least Concern.

    Nilgiri Flycatcher as Least Concern.

    White-winged Apalis as Near Threatened under criterion C2a(i).

    Whiskered Flowerpecker as Least Concern.

    Ursula’s Sunbird as Least Concern.

    Ankober Serin as Vulnerable under criterion C2a(ii).

    Kipengere Seedeater as Least Concern.

    Hispaniolan Crossbill as Vulnerable under criteria B2ab(i,ii,iii); C2a(i).

    Belding’s Yellowthroat as Vulnerable under criteria A2c+3c+4c; C2a(i).

    Zapata Sparrow as Vulnerable under criterion C2a(i).

    Cochabamba Mountain-finch as Endangered under criterion C2a(i).

    Azure-rumped Tanager as Near Threatened under criterion B2ab(i,ii,iii,v).

    The preliminary proposal for Mexican Woodnymph, Yellow-shouldered Amazon, Slaty Becard, Allpahuayo Antbird, Monteiro’s Bush-shrike, Munchique Wood-wren, Tanager Finch and Multicolored Tanager is to pend a decision until 2018 and so retain the current listing as part of the 2017 Red List update.

    There is now a period for further comments until the final deadline of 4 August, after which the recommended categorisations will be put forward to IUCN.

    Please note that we will then only post final recommended categorisations on forum discussions where these differ from the initial proposal.

    The final 2017 Red List categories will be published on the BirdLife and IUCN websites in early December, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  4. Praveen J says:

    May I point out that both Nilgiri and White-bellied Blue Robin should be under the same threat category ?
    I think there must be an error in BLI’s calculation of MCP (also in Joppa et al. 2016) for the Nilgiri Blue Robin that took it out of your consideration. It should be more than 12,000
    This BLI map is more or less correct.
    Can you relook at it please?

    • James Westrip (BirdLife) says:

      Thanks for the comment. The reason why Nilgiri Blue Robin has not been included in this topic is because Area of Occupancy data from Tracewski et al. (2016) shows that the Max AOO for this species would still meet the threshold for Endangered under criterion B2, and hence the species would not change Red List category, but its criteria string would. The values for White-bellied Blue Robin give a Max AOO that is greater than the threshold for Endangered, but it would still meet the threshold for Vulnerable under criteria B1 and B2.

      Tracewski, Ł.; Butchart, S. H. M.; Di Marco, M.; Ficetola, G. F.; Rondinini, C.; Symes, A.; Wheatley, H.; Beresford, A. E.; Buchanan, G. M. 2016. Toward quantification of the impact of 21st-century deforestation on the extinction risk of terrestrial vertebrates. Conservation Biology 30: 1070-1079.

  5. James Westrip (BirdLife) says:

    Recommended categorisations to be put forward to IUCN

    Following further review, the recommended categorisations for the following species have been changed.

    Taczanowski’s Tinamou, Black Guan, Bearded Guan, Rufous-headed Chachalaca, Gorgeted Wood-quail, Harwood’s Francolin, Santa Cruz Ground-dove, White-winged Nightjar, Hyacinth Visorbearer, Black-breasted Puffleg, Blossomcrown, Oaxaca Hummingbird, Hispaniolan Trogon, Red-fronted Parrotlet, Flores Hanging-parrot, Peruvian Plantcutter, Foothill Elaenia, Rufous Flycatcher, Moustached Antpitta, Choco Vireo, Palm Crow, Turner’s Eremomela, Bicol Ground-warbler, Black-hooded Laughingthrush, Vietnamese Cutia, Oberländer’s Ground-thrush, La Selle Thrush, Thyolo Alethe, White-bellied Blue-robin, White-winged Apalis, Ankober Serin, Hispaniolan Crossbill, Zapata Sparrow, Cochabamba Mountain-finch and Azure-rumped Tanager.

    A final decision for all of these species will now be pended until 2018 and so retain the current listing as part of the 2017 Red List update.

    The Red List category for Colorful Puffleg, Moheli Scops-owl, Cape Verde Swamp-warbler and White-throated Mountain Babbler will remain as outlined in the preliminary proposal but with criterion B1 added into the criteria string.

    The Red List category for Grand Comoro Scops-owl will remain as outlined in the preliminary proposal but with criteria B1 and C2a(ii) added into the criteria string.

    Decisions for all other species remain as outlined in the preliminary proposal.

    Final 2017 Red List categories will be published on the BirdLife and IUCN websites in early December, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  6. Simon Mahood says:

    Part 1 of 2 (because I exceeded the length limit for one post)

    Reading the new species account for Pale-throated Wren-babbler on the BirdLife website it indicates that it has been downlisted because: a. it is assumed that it occupies the entire Hoang Lien Son range in north western Vietnam and into China = a minor increase in EOO not triggering a status change, and, b. “four individuals that were assumed to be this species were observed Cenwanglaoshan Nature Reserve (1,400–1,600 m), north-west Guangxi, on 22–23 May 2002” = a massive increase in EOO.

    HBW treat the Guangxi record as a confirmed fact. The BirdLife factsheet references HBW rather than the original source, from which my text in quotation marks above is taken: it is in Forktail 22;


    • Simon Mahood says:

      Part 2 of 2 (because I exceeded the length limit for one post)

      The observers of the 2002 birds were cautious enough to state that they only “assumed” the birds to be Long-tailed Wren-babbler, presumably because they were evidently Spelaeornis in the Pale-throated/Grey-breasted/Chin Hills/Naga Wren-babbler complex, which was not split at the time. They made no attempt to assign them to a taxon within that complex, which was presumably done by Collar and Robson when writing HBW, based on geographic proximity. The paper does not state whether vocalizations were recorded nor why the observers weren’t certain about their identification, it is possible that the Guangxi birds represent an undescribed species.

      I think it was unwise to downlist Pale-throated Wren-babbler based on an increase in the EOO based almost entirely on one unconfirmed geographically-unlikely record. This species should be restored to VU based on a re-reassessment of the EOO to not include the Guangxi record. This record could be mentioned in the text with a note that if the population at that site is confirmed to be Pale-throated Wren-babbler then it should be downlisted to NT based on criterion B1 etc.

  7. James Westrip (BirdLife) says:

    Given the recent situation on Tinakula a re-examination of the Red List status of Santa Cruz Ground-dove is underway. As such the proposed change outlined in this topic is no longer relevant. If this re-examination suggests a potential change from its current Red List status, this will now instead be posted in a separate forum topic.

  8. Galo Buitrón-Jurado says:

    I have checked the categories for some Neotropical species, and I think they are very optimistic based in AOO new criteria. As example, Bearded Guan or Rufous-headed Chachalaca which are re-categorized as least concern. I believe that the analysis proposed before for the western ghats should be performed before re-assessment. For both species threats are mostly similar in their distribution range and they are threatened by increased pressure from mining and agriculture expansion, so new values projected by AOO is clearly misguided. It also did not include ecological differences of both species to threats. I am not completely sure if current density data exist for both species but I think that an estimate of 15000 Bearded Guan is very optimistic and not based in data available (Medina & Suarez 1994). Previous Birdlife estimates (2000) suggested only a population of less than 4000 individuals in Ecuador. I believe that as least without updated data of population sizes for forest based species, the AOO criteria is poorly recommended to uplist or downlist species.

    • Praveen J says:

      Using eBird Data I calculated EOO & AOO for these two species

      Bearded Guan:
      EOO (MCP): 29,651
      AOO (using squares of size 1/8th of a degree): 4,813

      Rufous-headed Chachalaca:
      EOO(MCP): 120,747
      AOO (using squares of size 1/8th of a degree): 15,786

      Hope these are useful

  9. Hannah Wheatley (BirdLife) says:

    Mario Rosina and Mónica Romo have provided the following comment via email:

    Status of Peruvian plantcutter (Phytotoma raimondii)

    The Peruvian plantcutter (Phytotoma raimondii) is a Peruvian endemic bird. A recent analysis of its population, verifies its rare occurrence, fragmentation of its habitat and intense threats (Romo et al. 2015 Presently, from 30 sites where it occurs, only six hold more than 10 individuals and three sites in which it reproduces. The results indicate the current population would be around 500 individuals. Sites where the bird occurs are very small (between 5 and 150 ha), very fragmented and separated from each other by long distances (from 60 to 280 km). Adding all these sites, it would certainly be less than 500 km2. These places are also in imminent danger of destruction due to urban and agricultural expansion, the change of land use for agro-industry, illegal logging, overgrazing and the introduction of exotic plant species (Tamarix sp) that competes and displaces the native vegetation. In addition a severe plague produced by the “white fly” or “sucking fly” (Enallodiplosis discordis) is seriously affecting the population of carob trees (Prosopis pallida) one of the key food resources.

    Due to the great fragmentation of its habitat and to the low population density where it is still found, using the method of “Area of Occupancy” AOO “is the most appropriate for this species and not the “Extent of Ocurrence” EOO as it was done before.

    The Peruvian Plantcutter should be kept in category ENDANGERED using criteria B2ab (I, II, III, IV) and not B1ab (I, II, III, IV) or C2a (I).

    Criteria B2ab..-Area of occupancy estimated to be less than 500 km2 and estimates indicating a) severely fragmented b) Continuing decline, observed, inferred or projected, in any of the following: (I) extent of occurrence (II) area of occupancy (III) area, extent and/or quality of habitat (IV) number of locations or subpopulations.

  10. Ricardo Cavalieri says:

    The Multicolored Tanager, according to Mr. Luis Renjifo, is not in immediate danger. Below is bis explanation:

    I am glad to hear about you interest in Multicolored Tanager, it is indeed one of my favorite Colombian birds, not only by its beautiful color an shape but also because its interesting behavior.

    Regarding your questions. The species is considered Vulnerable (the lower level of threat for a threatened species) because it has a small, fragmented and declining distribution. However, its habitat it is not declining rapidly. Instead it is under a long term decline. Some populations of the species are within well protected national parks or private reserves. Although whether these areas are enough to insure long term survival is not totally understood. But I can tell you that the species in not in an immediate danger of extinction.

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