Azure-rumped Tanager (Tangara cabanisi): revise global status?

BirdLife species factsheet for Azure-rumped Tanager: http://datazone.birdlife.org/species/factsheet/azure-rumped-tanager-tangara-cabanisi

This discussion was first published as part of the 2019 Red List update. At the time a decision regarding the status of this species was pended, but to enable potential reassessment of this species as part of the 2020 Red List update this post remains open and the date of posting has been updated.

Azure-rumped Tanager (Tangara cabanisi) occurs in the Sierra Madre de Chiapas of southern Mexico, and in south-western Guatemala (Heath and Long 1991, Collar et al. 1992, Eisermann et al. 2011). It is suggested to have a restricted distribution (see Cooper 2003, Eisermann and Avendaño 2007, Eisermann et al. 2011), within which it is locally common (M. Thompson in litt. 1998, Cooper 2003, Eisermann et al. 2011). It inhabits evergreen broadleaf forest (at 1,000-1,700m in Mexico, 860-1,900m in Guatemala), although has also been reported from plantations and edge habitat (Eisermann et al. 2011, Hilty and de Juana 2018). The species’s altitudinal range coincides with the best land for coffee growing, and while it does occur in plantations it is absent from the interior of intensive agriculture (Eisermann et al. 2011).

The species has been considered Endangered under Criterion B1ab(i,ii,iii,v) (see 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. The resulting EOO value now exceeds the thresholds required to maintain the species’s current listing, and as such it potentially cannot retain its current Red List status. Therefore, we have fully reviewed the species here against all criteria.

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) suggests that the area of suitable habitat for the species on average is declining by c.1.7% over three generations (14.7 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 this criterion. Therfore, Azure-rumped Tanager is assessed as Least Concern under Criterion A.

Criterion B – The newly calculated Extent of Occurrence (EOO) for this species is 10,400 km2. Tracewski et al. (2016) estimated the maximum Area of Occupancy (AOO) (calculated as the remaining tree area within the species’s range) to be c.2,520 km2. Therefore, the EOO meets the threshold for Vulnerable under Criterion B1, while the AOO approaches the threshold for Vulnerable under Criterion B2. To be listed under this criterion does require further conditions to be met though.

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. Therefore, conditions b(i,ii,iii,v) are met. However, the species is not known to undergo extreme fluctuations and so does not trigger condition c).

The species has been suggested to occur at only a limited number of localities (see BirdLife International 2018), yet records from eBird show a wider spread of records (eBird 2018). Based on IUCN definitions, the number of locations* where the species occurs is unlikely to meet the required thresholds. The species should not be considered severely fragmented per IUCN definitions (see IUCN Standards and Petitions Subcommittee 2017), although there is likely to be a degree of fragmentation of its habitat.

Thus, the species does not trigger sufficient conditions for listing as threatened under Criterion B. That said, it is possible that it approaches the thresholds required. As such, at worst, it may be very precautionarily thought to warrant listing as Near Threatened under Criteria B1ab(i,ii,iii,v)+2ab(i,ii,iii,v), although even this would be highly precautionary.

Criterion C – Based on surveys by Eisermann et al. (2011), the population in Guatemala is estimated to number 8,250-23,250 individuals (roughly equivalent to 5,500-15,500 mature individuals). However, the densities used in this study were from surveys at 1,400-1,900 m, where the species is most abundant. Therefore, the overall population size could fall either side of the threshold for Vulnerable (10,000 mature individuals), and precautionarily it could be estimated to be in the band 2,500-19,999 mature individuals to represent this uncertainty. Intuitively, this means that at the lower end of the band the species would meet the threshold for Vulnerable, but other conditions are required to warrant listing under Criterion C.

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. The map of sightings of this species on eBird suggests that the species occurs in either one or two subpopulations. If it were to be considered as two subpopulations, then the species would likely not warrant listing under Criterion C at all, as the largest subpopulation would probably contain significantly greater than 1,000 mature individuals. On the other hand, it could be precautionary to suggest that the species only occurs in one subpopulation, and then it would warrant a listing of Vulnerable under Criterion C2a(ii).

Criterion D – The species’s population size and range are likely too large to warrant listing under this criterion. Therfore, Azure-rumped Tanager is assessed as 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 precautionarily suggested that the species be listed as Vulnerable under Criterion C2a(ii). If further information or comment suggests that the species be considered to be in more than one subpopulation then, at worst, the species should be considered Near Threatened and potentially Least Concern. We welcome any comments, but 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: Tangara cabanisi. Downloaded from http://www.birdlife.org on 27/09/2018.

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. Available: http://www.ebird.org. (Accessed: Date [e.g., February 2, 2012]).

Eisermann, K.; Arbeiter, S.; López, G.; Avendaño, C.; Lux, J. de L. 2011. Distribution, habitat use and implications for the conservation of the Globally Threatened Azure-rumped Tanager Tangara cabanisi in Guatemala. Bird Conservation International 21: 423-437.

Eisermann, K.; Avendaño, C. 2007. Áreas propuestas para la designación como IBA (Área Importante para la Conservación de Aves) en Guatemala, con una priorización para la conservación adentro de las IBAs y una evaluación de las IBAs para aves migratorias Neárticas-Neotropicales.

Heath, M. F.; Long, A. J. 1991. Habitat, distribution and status of the Azure-rumped Tanager Tangara cabanisi in Mexico. Bird Conservation International 1: 223-254.

Hilty, S.; de Juana, E. 2018. Azure-rumped Tanager (Tangara cabanisi). 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. (retrieved from https://www.hbw.com/node/61676 on 28 September 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. 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.

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.

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11 Responses to Azure-rumped Tanager (Tangara cabanisi): revise global status?

  1. Red List Team (BirdLife International) says:

    Knut Eisermann kindly informed us of new records outside of the mapped range. For details, please see Eisermann and Avendaño 2019: An update on the inventory, distribution and residency status of bird species in Guatemala. Bull. B.O.C. 138: 148-229. We are currently revising the range map and calculating an updated value for the EOO.

    • Red List Team (BirdLife International) says:

      The species’s range map has been revised and now includes the new records of the species near Volcán Agua in Guatemala. Based on this map, the EOO of Azure-rumped Tanager has been recalculated as 10,100 km2. This still meets the threshold for Vulnerable. We assume that the species is undergoing a continuing decline in AOO, habitat quality and population size, but it is not restricted to few locations. As such, it may be listed as Least Concern or at most as Near Threatened under Criterion B1ab(ii,iii,v).

  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. It seems appropriate to use this space to share the main facts of all the information I provided to the BirdLife Red List team. Beside a new site record which slightly extends the range of Azure-rumped Tanager, I informed on numerous erroneous site records of Azure-rumped Tanager which had been included in the review process for this species, and I also provided the following data based on spatial analyses:

    – Size of the mapped area of current distribution: 2945 km2.

    – Size of Minimum Convex Polygon around all reliable site record: 5300 km2.

    – Extent of suitable habitat (humid broadleaf forest) within the area of distribution: 494 km2, which equals only 21% of the area of distribution (based on national vegetation coverage data from 2003 for Guatemala and 2011 for Mexico, and applying regional annual deforestation rates of 1%-1.4%).

    – Azure-rumped Tanager is now known from only 12 topographic units (a topographic unit being e.g. a volcano) throughout the range. Fragmentation of suitable habitat is severe and has worsened in the past 10 years.

    – Based on regionally determined deforestation rates, a 20% population decline of Azure-rumped Tanager can be expected in the next 14.7 year (3 generations).

    In conclusion, based on its restricted range and continuing decline of the extension of suitable habitat, Azure-rumped Tanager applies under some IUCN Red List criteria as Vulnerable and under some other criteria as Endangered. Remaining populations face continued and increasing threats, because of a complete lack of strictly protected areas within its range (IUCN protected area categories I and II). Thus, I recommended classification as Endangered under criteria EN B2b(ii+iii).

    Classifying Azure-rumped Tanager as Least Concern, as proposed by the Red List team, would mean that this bird, which is specialized on humid broadleaf forest, with a small range of less than 3000 km2 and less than 500 km2 of suitable habitat left within the range, with a population probably decreasing by 20% in next three generations, would be in the same category as Great-tailed Grackle (Quiscalus mexicanus) and House Sparrow (Passer domesticus).
    Two PDFs totaling 10 pages with details on the above summary are available upon request.

    • Red List Team (BirdLife International) says:

      Azure-rumped Tanager is not proposed to be listed as Least Concern. The proposal is that the species will be listed as Vulnerable under criterion C2a(ii).
      The final paragraph of your response is disappointing in that you have misunderstood the clearly stated proposal.

      The two area values that are used in assessing the status of a species are EOO and AOO: revisions to the map as received from Knut Eisermann resulted in an EOO (based on a Minimum Convex Polygon per the IUCN guidelines [IUCN 2012]) of 10,100km2, not 5,300km2. Regardless, both these values lie within the Vulnerable thresholds, such that the species does not qualify as Endangered. The additional subcriteria required to qualify under criterion B are that there is an ongoing decline (which is accepted), and that the number of locations (please see the definition) as defined by the main threat (deforestation) is fewer than 10 (which we do not consider to be true: locations are defined over a short timeframe and the extent of deforestation at each site is far smaller at this scale than the size of each topographic unit).
      AOO must be calculated at a 2x2km2 scale: this results in a value in excess of the 500km2 presented, despite great efforts to reduce this value below the threshold.

      We value the information provided highly and have revised our map based upon the suggestions contained. But the assessment proposed deviates from the IUCN guidelines.

  4. The Red List team’s post labelled 1 July 2019 was not visible on 3 July 2019. My post labelled 4 July 2019 was submitted on 3 July 2019 as response to the Red List team’s post labelled 26 June 2019. Since this is a moderated forum, with posts not being displayed right after submission, it would be expected and necessary to display posts in the correct chronological order.

  5. This is a reply to the Red List Team comment labelled July 4, 2019 at 4:28 pm:

    I’d like to make two statements here: 1) Please note that forum posts are not posted nor labelled in the correct chronological order. There was no clearly stated proposal online by Red List Team (RLT) on 3 July. RLT’s post labelled 26 June was the last post online before I submitted my post on 3 July (now labelled 4 July). And again, RLT’s post labelled 4 July was not online on 7 July. For a logical discussion it would be needed that BirdLife displays posts in the correct chronological order and indicates the real date when they were published in the forum. 2) In RLT’s post labelled 26 June, it is stated that the species would apply under Vulnerable because of the size of EOO (B1), but subcriteria (B1a-c) are not met, thus it would meet only criteria for Least Concern or Near Threatened in the B criterion. There was no statement about C criterion.

    I’d like to put up for discussion a summary of the process and the impact of a potential downgrading Azure-rumped Tanager from Endangered, where it was classified for many years. The mapped area of potential distribution has a size of 2945 km2, defined by the altitudinal belt of 900 to 1900 m on the Pacific slope of Guatemala and the Mexican state of Chiapas. The Minimum Convex Polygon around reliable site records has a size of 5300 km2. Humid broadleaf forest within the tanager’s range covers currently less than 500 km2, based on ground-truthed vegetation and land use mapping, taking into account the regional determined annual deforestation rates of up 1.4% since the mapping. The Minimum Convex Polygon around reliable site records should be taken as Extent of Occurrence (EOO), as it has been in previous assessments. The remaining habitat within the range could be taken as the Area of Occupancy (AOO).

    BirdLife’s calculation in this year results in an EOO of more than 10,000 km2 (by applying a Minimum Convex Polygon around the polygon of the area of distribution), which is almost double the size of the Minimum Convex Polygon surrounding the points of reliable site records. BirdLife’s calculation of the AOO, by applying a 2×2 km grid over forested area, results in more than 2500 km2, which is five times the size of the area of remaining habitat. The discrepancies between the EOO around site records (5300 km2) and BirdLife’s calculation of EOO (>10,000 km2), and between the true area of occupancy (area of available habitat) of 2500 km2) indicate that IUCN/BirdLife’s methodology may require some fine-tuning, for the Red List to represent threats in a more realistic way, particularly in cases where local fine-scale data are available. The EOO of less than 5000 km2 was in the past the trigger for listing this tanager under Endangered. The new EOO of 5300 km2 is slightly above this limit (and thus would meet Vulnerable), but the area of suitable habitat of <500 km2, if taken as AOO, would still meet Endangered criterion.

    Besides a new site record which slightly extents the area of distribution, nothing has positively changed in situ for the Azure-rumped Tanager in the past 8 years. The area of humid broadleaf forest continues to decline because of conversion to agricultural area, and not a single hectare of the area of distribution is strictly protected in protected areas of IUCN categories I and II. And yet, the political signal of a downgrade from Endangered would be that Azure-rumped Tanager is less threatened now than it was in the past decades. Such a misleading signal has the potential to accelerate forest destruction and fragmentation.

  6. There seem to be some serious problems in this forum software or in the forum moderation. The text submitted for my post labeled July had 608 words, but the version online has 601 words, with the third paragraph being manipulated. I re-post here the third paragraph:

    BirdLife’s calculation in this year results in an EOO of more than 10,000 km2 (by applying a Minimum Convex Polygon around the polygon of the area of distribution), which is almost double the size of the Minimum Convex Polygon surrounding the points of reliable site records. BirdLife’s calculation of the AOO, by applying a 2×2 km grid over forested area, results in more than 2500 km2, which is five times the size of the area of remaining habitat. The discrepancies between the EOO around site records (5300 km2) and BirdLife’s calculation of EOO (>10,000 km2), and between the true area of occupancy (area of available habitat) of 2500 km2) indicate that IUCN/BirdLife’s methodology may require some fine-tuning, for the Red List to represent threats in a more realistic way, particularly in cases where local fine-scale data are available. The EOO of less than 5000 km2 was in the past the trigger for listing this tanager under Endangered. The new EOO of 5300 km2 is slightly above this limit (and thus would meet Vulnerable), but the area of suitable habitat of <500 km2, if taken as AOO, would still meet Endangered criterion.

  7. For a second time my re-post does not completely represent what I submitted. Some words are missing, which changes the meaning of the paragraph. It is difficult to have a clear discussion based on scientific data if your forum system keeps erasing words in the posts. It is important to fix that, if you are asking volunteers for feedback on important issues such as the Red List.

  8. Paula Enríquez says:

    Azure-rumped Tanager is distributed in humid broadleaf forest as the optimal habitat (Eisermann et al. 2011), but it has also been recorded in secondary forest and coffee plantations. In Mexico, this tanager has only been recorded in a narrow altitudinal belt of two areas; El Triunfo and Tacaná Biosphere Reserves, in cloud forests but also in neighboring pine forest.

    The relative abundance estimated for Tangara cabanisi in Santa Rita, El Triunfo Biosphere Reserve in 2004 was 0.84 ind/km2 (SEMAVIHN 2011 data; Enríquez et al. 2013). The Secretary of Environment and Natural History of Chiapas has been conducting a monitoring study for fauna for several years. Tangara cabanisi has been recorded at Tacaná Volcano in cloud forest in 2008 and 2009 with very few records, more records have been in El Triunfo Biosphere Reserve.

    The main threat for Azure-rumped Tanager is the forest fragmentation and habitat reduction. Other potential threats are tropical storms and hurricanes that change also the structure of vegetation, forest fires in the area are reported with an increasing number during the dry seasons in the area,, for example in 2019 more than 220 ha were lost at El Triunfo (Triunfo Reserve managers). Another potential threat is opencast mining, with most mining concessions located in the southern part of the El Triunfo Biosphere Reserve, exploring and exploiting copper, silver, gold, and titanium (Godínez-Gómez and Mendoza 2019).

    In Mexico, T. cabanisi is considered a species in peril of extinction (P; SEMARNAT 2010) because of its range of distribution is very limited, its abundance is from rare to uncommon, it is associated to humid forests, and its habitat is highly endangered.

    Eisermann, K., S. Arbeiter, G. López, C. Avendaño, y J. de León Lux. 2011. Distribution, habitat use, and implications for the conservation of the globally threatened Azure-rumped Tanager Tangara cabanisi in Guatemala. Bird Conservation International 21: 423-437.
    Enríquez, P.L., J.L. Rangel-Salazar, J.R. Vázquez Pérez y R. Partida Lara. 2013. Distribución, abundancia y selección de hábitat de especies de aves amenazadas y en peligro de extinción en los bosques de montaña de Chiapas. El Colegio de la Frontera Sur. Informe final SNIB-CONABIO, proyecto HK007. México D. F.
    Godínez-Gómez, O. y E. Mendoza. 2019. Amenazas a la biodiversidad de la Reserva de la Biósfera El Triunfo. Pp. 187-194 En P.L. Enríquez, R. Martínez-Camilo y M. Carrillo García (eds.). La Reserva de la Biósfera El Triunfo: avances y necesidades de investigación y conservación. ECOSUR. San Cristóbal de Las Casas, Chiapas. México.
    Long, A.J. y M.F. Heath. 1994. Nesting ecology and helping behavior in the Azure-rumped Tanager in Mexico. Condor 96: 1095-1099.
    SEMARNAT. 2010. Norma Oficial Mexicana 059- SEMARNAT 2010. Protección ambiental especies nativas de México de flora y fauna silvestres. Categorías de riesgo y especificaciones para su inclusión, exclusión, o cambio. Lista de especies en riesgo. Diario Oficial de la Federación. 30 diciembre 2010. México D. F.
    SEMAVIHN (Secretaría de Medio Ambiente, Vivienda e Historia Natural). 2011. Base de datos Proyecto Monitoreo Biológico y Social en Áreas Naturales Protegidas. Tuxtla Gutiérrez, Chiapas.

  9. Claudia Hermes (BirdLife International) says:

    Recommended categorisations to be put forward to IUCN

    Based on available information, our proposal for the 2019 Red List is to pend the decision on this species and keep the discussion open until 2020, while leaving the current Red List category unchanged in the 2019 update.
    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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