Forbes’s Blackbird (Anumara forbesi): revise global status?

BirdLife species factsheet for Forbes’s Blackbird

The Forbes’s Blackbird (Anumara forbesi) is known from widely scattered sites in Brazil, where it occurs in Pernambuco and Alagoas in the northeast, and over 1,400 km to the south in Minas Gerais, east Brazil. It inhabits forests, forest edge, adjacent marshy areas and river edges and sugarcane and mango plantations (Fraga & Sharpe 2016).

Widespread habitat destruction, particularly in north-east Brazil, through conversion to agriculture, has caused considerable habitat loss and degradation, and even reduced forest-edge areas. However, the species might be able to withstand forest conversion to plantations to some degree. Other potential threats are trapping and nest parasitism by Molothrus species.

The species is currently listed as Endangered under Criterion B2. However, the species’s AOO has not been quantified so the species requires reassessment. Our current information on the species’s conservation status will now be compared to all Red List Criteria.

Criterion A – The area of forest with at least 30% canopy cover within the species’s mapped range declined by 12% over a period of three generations (13 years; Bird et al. 2020)* from 2005-2018 (Global Forest Watch 2020). However, the species is known to inhabit forest edges as well as sugar cane and mango plantations, and non-forest habitats, so it is not known whether the reduction in forest habitat has resulted in a similar reduction in population size. The population size is suspected to be declining, but there is insufficient information to assess a rate of decline. The species cannot be assessed under this criterion.

Criterion B – The species’s extent of occurrence (EOO) is inferred to be 691,000 km2, based on a minimum convex polygon around the mapped range. This does not approach the threshold for listing the species as threatened under Criterion B1. The area of occurrence (AOO) has not been quantified. The species’s mapped range has a total area of 137,270 km2, and in 2010, there were 43,900 km2 of forest with at least 30% canopy cover within the area of the species’s mapped range (Global Forest Watch 2020). Although the species has a localised and fragmented distribution within the mapped range, we do not have evidence that the AOO is less than 2,000 km2. The species is assessed as Least Concern under Criterion B.

Criterion C – The species appears to be naturally rare and has localised subpopulations. There is little data on the population, but the total population size is thought to be 1,000-2,499 individuals (de Melo Dantas & Albano 2018), which roughly equates to 667-1,667 mature individuals, placed in the band 600-1,700 mature individuals. The species meets the initial population size threshold for listing as Endangered under Criterion C. To list the species as threatened on the Red List under Criterion C, further conditions would also need to be met.

There must also be evidence from which to infer that the species’s population size is undergoing a continuing decline. Although remote-sensed data indicates that the amount of forest within the species’s range is declining (Global Forest Watch 2020), the species is known to inhabit forest edges as well as sugar cane and mango plantations, and non-forest habitats. Therefore, although we may suspect that the population is declining, we do not consider there to be sufficient evidence from which to infer a continuing decline for the purpose of applying Criterion C.

The species is found in localised subpopulations separated from large areas of unsuitable habitat, and there are no records of individuals moving large distances between habitat patches (de Melo Dantas & Albano 2018). The species is therefore thought to have small subpopulations with fewer than 1,000 mature individuals in each subpopulation (de Melo Dantas & Albano 2018). Condition a(i) is met at the level of Vulnerable. Less than 90% of individuals are found in any one subpopulation, meaning that the species does not meet condition a(ii). There is no evidence that the species’s population size is undergoing extreme fluctuations so the species doesn’t meet condition b.

Although the population size falls beneath the threshold for listing the species as Endangered under Criterion C, the population size is suspected to be declining, and condition a(i) is met at the level of Vulnerable, there is insufficient evidence to be able to infer a continuing decline. The species therefore qualifies as Near Threatened, approaching the threshold for listing as threatened under Criterion C2a(i).

Criterion D – Based on the population estimates described above (600-1,700 mature individuals), the species may qualify for listing as Vulnerable or Near Threatened under Criterion D1, depending on whether the true population size is most likely to be above, or below 1,000 mature individuals. The species does not have a restricted area of occupancy or number of locations such that a threat could drive the species to Critically Endangered or Extinct within a very short time. The species does not meet the criteria for listing as Vulnerable under Criterion D2.

Criterion E – To the best of our knowledge no quantitative assessment of the probability of extinction has been conducted for this species, and so it cannot be assessed against this criterion.

Based on the above assessment, it is proposed to list Forbes’s Blackbird (Anumara forbesi) as Vulnerable under Criterion D1. However, should evidence arise that indicates that the population size is more likely to be greater than 1,000 mature individuals, the species may be listed as Near Threatened under Criteria C2a(i); D1. We welcome any comments to the proposed listing. Information is particularly requested on the species’s population size and trend.

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’s Red List status. Therefore, please make sure your comments are about the proposed listing. By submitting a comment, you confirm that you agree to the Comment Policy.

*Bird generation lengths are estimated using the methodology of Bird et al. (2020), as applied to parameter values updated for use in each IUCN Red List for birds reassessment cycle. Values used for the current assessment are available on request. We encourage people to contact us with additional or improved values for the following parameters; adult survival (true survival accounting for dispersal derived from an apparently stable population); mean age at first breeding; and maximum longevity (i.e. the biological maximum, hence values from captive individuals are acceptable).

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

Bird, J. P.; Martin, R.; Akçakaya, H. R.; Gilroy, J.; Burfield, I. J.; Garnett, S.; Symes, A.; Taylor, J.; Šekercioğlu, Ç.; Butchart, S. H. M. (2020). Generation lengths of the world’s birds and their implications for extinction risk. Conservation Biology online first view.

de Melo Dantas, S. & Albano, C. 2018. Anumara forbesi (Sclater, 1886). In: Instituto Chico Mendes de Conservação da Biodiversidade (ed.), Livro Vermelho da Fauna Brasileira Ameaçada de Extinção: Volume III – Aves, pp. 566-568. Brasília.

Fraga, R.; Sharpe, C.J. 2016. Forbes’s Blackbird (Curaeus forbesi). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. and de Juana, E. (eds), Handbook of the Birds of the World Alive, Lynx Edicions, Barcelona.

Global Forest Watch. 2020. Interactive Forest Change Mapping Tool. Available at: http://www.globalforestwatch.org/.

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6 Responses to Forbes’s Blackbird (Anumara forbesi): revise global status?

  1. Red List Team (BirdLife International) says:

    Global Forest Change data on tree cover loss up to 2019 have now been released and made available via Global Forest Watch. Based on these data, the area of forest with at least 30% canopy cover within the species’s mapped range declined by 11% over a period of three generations (13 years) from 2006-2019 (Global Forest Watch 2020). This new information does not change the conclusions of the above ssessment.

  2. Luiz Gabriel Mazzoni says:

    I recon there is a need to reassess this species’ current status. However, I am concerned by the information used to justify some of the criterions, especially criterion B and C. I was asked to help in the review of this species’ factsheet and I found that some erroneous records of the taxa are still being taken into account. The factsheet of this species’ mention: “…near Pirapora (E.O. Willis in litt. 1999), and the borders of Parque Nacional Cavernas do Peruaçu (Vasconcelos et al. 2006)”, even though the records of Forbes’s Blackbird from northern Minas Gerais lack any documentation and have been already disregarded, since those are probably based on misidentifications (see Mazzoni et al. 2012).

    If this allegedly subpopulation from northern Minas Gerais was taken into account to meet criteria b and c, then the analysis is most probably biased, for it was based on anectodal and undocumented data. Furthermore, to my knowledge there are no records of the species within any conservation unit in Minas Gerais, so the southern subpopulation of the taxa is not currently under protection, which should also be taken into consideration.

    Based on this, I recommend that we are conservative and maintain the current conservation status for this species (endangered).

    Cited reference:

    Mazzoni, L. G., Esser, D., de Carvalho Dutra, E., Perillo, A., & Morais, R. (2012). New records of the Forbes’s Blackbird Curaeus forbesi (Sclater, 1886) in the state of Minas Gerais, with comments on its conservation. Revista Brasileira de Ornitologia, 20(1), 44-47.

  3. A meta-analysis by Fabio Costa et al in 2018 indicated that this species also occur in the illegal bird trade in Brazil. https://www.researchgate.net/publication/327356585_Especies_de_Aves_Traficadas_no_Brasil

  4. Red List Team (BirdLife International) says:

    Many thanks to everyone who has contributed to this discussion. We greatly appreciate the time and effort invested by so many people in commenting. The window for consultation is now closed. We will analyse and interpret the new information and post a preliminary decision on this species’s Red List status on this page in early July.

    Thank you once again,
    BirdLife Red List Team

  5. Red List Team (BirdLife International) says:

    Preliminary proposal

    Thank you for the comments on this proposal. Based on the comments received about the doubt over the records in northern Minas Gerais, and according to Mazzoni et al. (2012), the geographic range information for this species has been updated as follows: ‘Anumara forbesi is known from widely scattered sites in Brazil, where it occurs in Pernambuco and Alagoas in the northeast, and over 1,400 km to the south in Minas Gerais, east Brazil. There is some doubt over the identification of records from northern Minas Gerais and these records require further verification (Mazzoni et al. 2012, L. G. Mazzoni in litt. 2020).’ The distribution map has also been revised, but we originally based the new map partly on the map presented in the 2018 Livro Vermelho (de Melo Dantas & Albano 2018), which includes some records in northern Minas Gerais. Following further consideration, we have now removed part of the mapped range in northern Minas Gerais, according to Mazzoni et al. (2012). This produces the following changes to the assessment:

    Criterion A: The area of forest with at least 30% canopy cover within the species’s mapped range declined by 10% over a period of three generations (13 years; Bird et al. 2020)* from 2006-2019 (Global Forest Watch 2020). This does not change the assessment under this criterion.

    Criterion B: The species’s extent of occurrence (EOO) is inferred to be 447,000 sqkm, based on a minimum convex polygon around the mapped range. The species’s mapped range has a total area of 81,732 sqkm, and in 2010, there were 25,300 sqkm of forest with at least 30% canopy cover within the area of the species’s mapped range (Global Forest Watch 2020). This does not change the assessment under this criterion.
    We also note that although the Livro Vermelho population estimate was 1,000-2,499 individuals, this was uncertain, and the population was considered with high certainty to be smaller than 10,000 mature individuals (de Melo Dantas & Albano 2018). Since this estimate has not been derived from quantitative surveys, it may not be robust enough for a listing of threatened under Criterion C.

    We will note in the threats information of the assessment that the species has been observed in trade.

    Based on available information, our preliminary proposal for the 2020 Red List would be to list Forbes’s Blackbird as Near Threatened, approaching the thresholds for Criteria C2a(i); D1.

    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 2020 Red List categories will be published on the BirdLife and IUCN websites in December 2020 or January 2021, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  6. Luiz Gabriel Mazzoni says:

    I find it risky to downlist this species from Endangered to Near Threatened. I recon the final decision is up to the red list team, and I respect their decision. However, there is a lack of data concerning population size (especially mature individuals from Minas Gerais) and a lack of records within conservation units (at least in Minas Gerais). Furthermore, the two subpopulations are at least 1,400 km apart, and a quick search at Wiki Aves (wikiaves.com.br) reveals only 11 localities with records of the species in each subpopulation. To place its population in the band between 2,500 – 10,000 mature individuals, let’s arbitrarily assume 2,500 mature individuals in each subpopulation. Considering I never heard of groups with more then 20-30 birds in Minas Gerais (at least recently) I find this assumption somewhat risky. In my opinion (not based on quantitative criteria) it should be kept as Vulnerable, in accordance to the Brazilian Red Book.

    Best regards,

    Luiz Gabriel Mazzoni

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