Archived 2019 topic: Multicolored Tanager (Chlorochrysa nitidissima): revise global status?

BirdLife species factsheet for Multicolored Tanager

Multicolored Tanager (Chlorochrysa nitidissima) occurs in the western and north-central Andes of Colombia. It ranges from 1,300 to 2,200 m, exceptionally as low as 1,140 m in the north-central Andes and 900 m in the western Andes (Collar et al. 1992). The majority of records are from the western Andes in the Valle del Cauca. Formerly common, the species is now infrequently recorded. It, however, remains locally fairly common, even in remnant forest fragments. Multicolored Tanager inhabits humid, mossy, montane forest and forest edges, and also occurs regularly in mature secondary forest and clearings with a few large trees left standing.

The main threat to the species is the loss and fragmentation of the forests within its range. Deforestation has been severe in many parts of the range, notably in and around the Valle del Cauca and around Medellín (Wege and Long 1995, Salaman and Stiles 1996). Forests are lost to mining developments, human settlements, small-scale agriculture and the rapid expansion of the road network, which is opening up more remote parts of the species’s range to encroachment (Salaman and Stiles 1996, Stiles 1998). However, large blocks of primary forest still persist (Wege and Long 1995, Stiles 1998).

Multicolored Tanager is currently listed as Vulnerable 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 Multicolored Tanager, this 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.3.4% over three generations (11.1 years). We can tentatively assumed that the rate of population decline is equivalent to the rate of forest loss. 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 this criterion. Multicolored Tanager may be listed as Least Concern under Criterion A.

Criterion B – The newly calculated Extent of Occurrence (EOO) for this species is 51,200 km2. This is too large to warrant listing under Criterion B1. For the Area of Occupancy (AOO) of Multicolored Tanager, the national Red List of Colombia gives two values: The AOO excluding the western part of the distribution range amounts to c. 2,200 km2, while the total AOO covers c. 5,500 km2 (Renjifo et al. 2014). Tracewski et al. (2016), on the other hand, estimated the remaining tree area within the species’s range to be c. 10,900 km2. This value represents a proxy for the maximum AOO. Thus overall, Multicolored Tanager cannot be considered threatened under Criterion B2.

In order to be listed as Near Threatened, there must be evidence that the AOO of the species is closer to the lowest value given (2,200 km2; Renjifo et al. 2014). However, this seems unlikely, as records from eBird show a wide spread, particularly in the western Cordillera of the Andes (eBird 2018); and thus there is no reason to exclude the western part of the range from the AOO value. The apparent rarity of the species on the western slopes of the western Cordillera (see Renjifo et al. 2014) is not relevant for Criterion B2, as the AOO specifies the area occupied by a taxon, regardless its abundance (IUCN 2012). It is therefore conceivable that the total AOO is at least 5,500 km2 (Renjifo et al. 2014), and at maximum 10,900 km2 (per Tracewski et al. 2016). Thus, Multicolored Tanager does not approach the threshold for listing as threatened and may be considered Least Concern under Criterion B.

Criterion C – Acknowledging the need for a more precise population estimate, BirdLife International (2018) placed the population size of Multicolored Tanager in the band 20,000-49,999 individuals. This roughly equates to 13,000-35,000 mature individuals. Based on an observed density of 13-15 individuals per km2 (Cárdenas et al. 2008, Fierro et al. 2009), Renjifo et al. (2014) report a population of 26,000 individuals, equating to c. 17,000 mature individuals. However, the density used by Renjifo et al. (2014) were from places where the species is presumably most abundant, acknowledging that the estimate given might be too high. Therefore, we can tentatively assume that the true population size may be closer to the lower estimate given by BirdLife International (2018) of 13,000 mature individuals. Under this assumption the species approaches, but does not meet, the threshold for Vulnerable (10,000 individuals).

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. The species is not known to undergo extreme fluctuations, so it does not trigger the conditions for Criterion C2b. However, the rate of population decline can be inferred from the rate of habitat loss (3.4% over three generations; Tracewski et al. 2016). Furthermore, it is assumed that no subpopulation consists of more than 1,000 mature individuals (Renjifo et al. 2014). Therefore, Multicolored Tanager may be listed as Near Threatened under Criterion C2a(i).

Criterion D – The species’s population size and range are likely too large to warrant listing as threatened, and thus Multicolored Tanager 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 Multicolored Tanager (Chlorochrysa nitidissima) be listed as Near Threatened, approaching the threshold for listing as Vulnerable under Criterion C2a(i). 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.

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: Chlorochrysa nitidissima. www.birdlife.org (Accessed 02 October 2018).

Cárdenas, G.; Johnston, R.; Cadena, G.; Fierro-Calderón, E. 2008. Iniciativa de evaluación para aves amenazadas y endémicas del valle medio del río Cauca. Informe Final. Wildlife Conservation Society-wcs Programa Colombia. Cali, Colombia.

Fierro, K.; Motalegre, C.; Fierro, E.; Eusse, D. 2009. Five threatened species in the Western Andes of Colombia. Final report for the Conservation Leadership Programme. Asociación Calidris. Cali, Colombia.

Collar, N. J.; Gonzaga, L. P.; Krabbe, N.; Madroño Nieto, A.; Naranjo, L. G.; Parker, T. A.; Wege, D. C. 1992. Threatened birds of the Americas: the ICBP/IUCN Red Data Book. International Council for Bird Preservation, Cambridge, U.K.

eBird. 2018. eBird: An online database of bird distribution and abundance [web application]. eBird, Ithaca, New York. http://www.ebird.org (Accessed 02 October 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.

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

Stiles, F. G. 1998. Notes on the biology of two threatened species of Bangsia tanagers in northwestern Colombia. Bulletin of the British Ornithologists’ Club 118: 25-31.

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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1 Response to Archived 2019 topic: Multicolored Tanager (Chlorochrysa nitidissima): revise global status?

  1. 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.

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