Archived 2019 topic: Choco Vireo (Vireo masteri): revise global status?

BirdLife species factsheet for Choco Vireo

Choco Vireo (Vireo masteri) occurs in the Chocó region on the Pacific slope of the West Andes of Colombia and north-western Ecuador and is known from only four disjunct sites (Brewer 2018). Although it cannot be ruled out that Choco Vireo occurs in suitable habitat between these sites (Salaman and Stiles 1996, Renjifo et al. 2002), searches in intermediate areas so far have failed to find the species (P. Salaman in litt. 1999, 2000, 2003). A precautionary estimate places its population size in the band 14,200-17,000 mature individuals (Jahn et al. 2007).

In Colombia, Choco Vireo is restricted to wet primary cloud-forest, favouring steep slopes and areas with much epiphytic growth, open canopy and tree-fall gaps (Renjifo et al. 2014, Brewer et al. 2018). It occurs between 1,200 and 1,600 m (Brewer et al. 2018). In Ecuador, the species uses a wider range of habitats, including wet primary forest, as well as forest edges bordering pastures, roads, railways and re-growth of intensively logged forest, between 800 and 1,500 m (Jahn et al. 2007).

The range and population of Choco Vireo are in decline as a consequence of habitat destruction. Deforestation has been intensified in the Chocó region since the 1970s, mainly because of increased colonisation and development. The expansion of the road network has intensified the impact of logging, small-scale agriculture and gold mining, particularly at lower altitudes (Salaman 1994, Wege and Long 1995, Salaman and Stiles 1996).

Choco Vireo is currently listed as Endangered under Criterion B1ab(i,ii,iii,v) (BirdLife International 2018). However, this is no longer tenable because this was based on an Extent of Occurrence (EOO) value calculated as the ‘area of mapped range’. This is no longer appropriate, and the EOO should be calculated using a Minimum Convex Polygon (see IUCN 2001, 2012, Joppa et al. 2016), as EOO is a measure of the spatial spread of areas occupied by a species, not the actual area it occupies. After re-calculating the EOO for Choco Vireo, the species appears to warrant a change in Red List status. Therefore, we present here our reassessment against all criteria for the species.

The initial topic on this analysis can be found here.

Criterion A – The population trend for this species has not been directly estimated. However, deforestation data from between 2000 and 2012 (Tracewski et al. 2016) suggest that the area of suitable habitat for the species on average is declining by c.2.7% over three generations (12.6 years). Therefore, while it may be possible to consider the species to be in decline, the rate of decline is likely to be slow and would not approach the threshold for Vulnerable under Criterion A. Therefore, Choco Vireo may be listed as Least Concern under this criterion.

Criterion B – The newly calculated Extent of Occurrence (EOO) for this species is 34,500 km2. This is too large for listing as threatened under Criterion B1. Tracewski et al. (2016) estimated the remaining tree area within the species’s range to be c.2,350 km2. We can tentatively assume that for a forest-dependent species like Choco Vireo, the area of forested habitat roughly equates to the maximum Area of Occupancy (AOO). As such the maximum AOO likely approaches the threshold for Vulnerable under criterion B2 (AOO < 2,000 km2). However, to be listed under this criterion, further conditions have to be met.

The species is suspected to occur at a very limited number of localities (BirdLife International 2018). However, records from eBird show a wide spread (eBird 2018), and it is unclear if the number of locations* of occurrence meets the threshold for listing as Vulnerable under condition (a) (≤10 locations). However, it is possible that Choco Vireo approaches this threshold. Even though its habitat shows a high level of fragmentation, the species should not be considered severely fragmented per IUCN definition (see IUCN Standards and Petitions Subcommittee 2017). Given the ongoing threats, we can assume that there is an ongoing decline in the species’s EOO, AOO and quality/extent of habitat, and can infer an ongoing population decline too, so that condition b(i,ii,iii,v) is met. However, the species is not known to undergo extreme fluctuations and so does not meet condition (c).

Overall, Choco Vireo does not trigger sufficient conditions for listing as threatened under criterion B. However, it likely approaches the thresholds required. As such, it may be listed as Near Threatened under Criterion B2ab(i,ii,iii,v).

Criterion C – Based on density estimates for its Ecuadorian range, the global population of Choco Vireo has been extrapolated to 15,600 ± 1,400 mature individuals (Jahn et al. 2007). This is too large to warrant listing as threatened under Criterion C. Given that the species is considered to be in decline, however, it is likely that the population size approaches the threshold for Vulnerable under this criterion (<10,000 mature individuals). Yet, in order to be listed under Criterion C, other conditions have to be met.

The rate of decline in the species has not been directly estimated, and so Criterion C1 cannot be used. Choco Vireo occurs in four subpopulations (two each in Colombia and Ecuador). These subpopulations likely consist of more than 1,000 mature individuals each; so the species does not meet the conditions 2a(i) or 2a(ii). Moreover, the species is not known to undergo extreme fluctuations, and thus does not trigger condition 2b. Therefore, Choco Vireo may be listed as Least Concern under Criterion C.

Criterion D – The species’s population size and range are too large to warrant listing as threatened, and thus Choco Vireo may be considered Least Concern under Criterion D.

Criterion E – To the best of our knowledge, there has been no quantitative analysis of extinction risk conducted for this species. Therefore, it cannot be assessed against this criterion.

Therefore, it is suggested that Choco Vireo (Vireo masteri) be listed as Near Threatened, approaching the threshold for listing as Vulnerable under Criterion B2ab(i,ii,iii,v). We welcome any comments on the proposed listing.

Please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of the species’ Red List status. Therefore, please make sure your comments are relevant to the species’ Red List status and the information requested.

*The term ‘location’ refers to a distinct area in which a single threatening event can rapidly affect all individuals of the taxon present, with the size of the location depending on the area covered by the threatening event. Where a taxon is affected by more than one threatening event, location should be defined by considering the most serious plausible threat (IUCN 2001, 2012).

An information booklet on the Red List Categories and Criteria can be downloaded here and the Red List Criteria Summary Sheet can be downloaded here. Detailed guidance on IUCN Red List terms and definitions and the application of the Red List Categories and Criteria can be downloaded here.

References

BirdLife International. 2018. Species factsheet: Vireo masteri. www.birdlife.org (Accessed 02/10/2018).

Brewer, D. 2018. Choco Vireo (Vireo masteri). In: del Hoyo, J.; Elliott, A.; Sargatal, J.; Christie, D.A.; de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona, Spain. https://www.hbw.com/node/61260 (Accessed 03/10/2018).

eBird. 2018. eBird: An online database of bird distribution and abundance [web application]. eBird, Ithaca, New York. http://www.ebird.org (Accessed 03/10/2018).

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. 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. http://www.iucnredlist.org/documents/RedListGuidelines.pdf

Jahn, O.; Palacios, B.; Valenzuela, P. M. 2007. Ecology, population and conservation status of the Chocó Vireo Vireo masteri, a species new to Ecuador. Bulletin of the British Ornithologists’ Club 127(2): 161-166.

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.

Renjifo, L.M.; Gómez, M.F.; Velásquea-Tibatá, J.; Amaya-Villareal, A.M.; Kattan, G.H.; Amayal-Espinel, J.D.; Burbano-Girón, J. 2014. Libro Rojo de Aves de Colombia, Vol. I: Bosques Húmedos de los Andes y de la Costa Pacífica. Editorial Pontificia Universidad Javeriana e Instituto Alexander von Humboldt. Bogotá, Colombia.

Salaman, P.G.W. 1994. Surveys and Conservation of Biodiversity in the Chocó, south-west Colombia. BirdLife International, Cambridge, U.K.

Salaman, P.G.W.; Stiles, F.G. 1996. A distinctive new species of vireo (Passeriformes: Vireonidae) from the Western Andes of Colombia. Ibis 138: 610-619.

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. Wege, D.C.; Long, A.J. 1995. Key Areas for Threatened Birds in the Neotropics. BirdLife International, Cambridge, U.K.

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7 Responses to Archived 2019 topic: Choco Vireo (Vireo masteri): revise global status?

  1. Juan Freile says:

    I suspect the newly calculated EOO is overestimating the species EOO. Further, this species EOO is actually fragmented. Probably not severely fragmented, but fragmented. If you see eBird records (even if all are accepted as valid), there are 3-4 “populations” separated by large expanses with no records. Actually, regions with no records are in SW Colombia and NW Ecuador are nearly larger (or even larger) than areas with positive records.
    Downgrading it to NT will underestimate the actual status of this species (as also occurs with several other Choco endemics).

    • Red List Team (BirdLife International) says:

      Thank you very much for your comment. IUCN guidelines state that the EOO has to be mapped as a Minimum Convex Polygon around the area of mapped range. The guidelines stress that this polygon needs to be continuous, and that no exceptions can be made for species with disjunct ranges. The EOO is always continuous per IUCN definition; it cannot be fragmented. This implies that for Chocó Vireo, the EOO will include areas of unsuitable habitat, which cannot be excluded. Please see https://www.iucnredlist.org/resources/redlistguidelines chapter 4.9 for details. The EOO measures the spatial spread of the areas occupied by the taxon, i.e. the spatial spread of the extinction risk. It does not measure the amount of occupied or suitable habitat.

    • I agree with Juan that NT will underestimate the actual status of this species. For the reasons that Juan is giving but also because the deforestation estimate of “only” 2.7% over 12.6 years is almost certainly too benign. New deforestation analyses (Finer et al. 2019) show that 68% of Chocó forest has already been lost in Ecuador. The deforestation estimate for the altitudinal range of Chocó Vireo is slightly better with only 50% lost. More specifically, this analysis showed that 20% of the forest were lost since 1990. The deforestation rate in the southern part of the species’ range is thus much higher than what the NT assessment is based upon. Further, deforestation rate increased strongly in Colombia.
      VU status is surely merited based on Criteria A.

      • Red List Team (BirdLife International) says:

        Thank you very much for your comment. You are right in that the deforestation rates reported by Tracewski et al. (2016) potentially underestimate the rate of forest loss for species that occupy a narrow altitudinal range.
        We have now reviewed the information presented by Finer et al. (2019). They report a rate of forest loss of 20% between 2000 and 2018 in the Chocó of northern Ecuador. While they however state that forest loss mostly occurred in the lowlands, i.e. below the range of Chocó Vireo, we can precautionarily base the assessment on this value, assuming that forest loss amounts to 20% between 2000 and 2018 throughout the entire range. Assuming furthermore that the population decline is proportional to the deforestation rate, we can infer that the species declined by 14.5% over the last three generations.
        While this estimate is much larger than the value reported in the initial assessment of the species, it however does not meet or approach the threshold for Vulnerable under Criterion A.

  2. Red List Team (BirdLife International) says:

    Preliminary proposal
    Based on available information, our preliminary proposal for the 2019 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.
    Please note that we will then only post final recommended categorisations on forum discussions where these differ from those in the initial proposal.
    The final 2019 Red List categories will be published on the BirdLife and IUCN websites in December, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  3. Thomas Donegan says:

    I agree with the comments made by discussion participants and disagree with the downgrading of this species. The species appears to be absent from several sites which have been well studied e.g. Munchique/Tambito. There is probably something odd going on in terms of ecology or habitat specialisms here that we don’t yet understand. This is a very rare species – only discovered in the 1990s despite extensive historical collecting activities in the West Andes and despite it being so distinctive and “widely” distributed.

    • Red List Team (BirdLife International) says:

      Thank you for your comment. The proposed downlist of this species is based on the information that the EOO is larger than previously assumed, not meeting the threshold for EN or VU anymore. The EOO is a purely spatial measure, which does not take into account the density of the species; hence also a patchily distributed species can have a large EOO.

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