Black-hooded Antwren (Formicivora erythronotos): request for information

BirdLife species factsheet for Black-hooded Antwren

The Black-hooded Antwren (Formicivora erythronotos) is found in a narrow coastal strip around the Ilha Grande bay in south Rio de Janeiro state, Brazil. Although known from c.20 specimens collected in the 19th century, it was unrecorded for over 100 years until its rediscovery in 1987 in the Angra dos Reis area of the Ribeira bay. It has now been recorded at a total of seven sites along the bay of Ilha Grande and in Serra do Piloto (Gonzaga 2008), within the municipalities of Angra dos Reis and Paraty (Buzzetti 1998, E. Mendonça and L. P. Gonzaga in litt. 2000): Ariró, Vale do Mambucaba, Bracuí, Frade, São Gonçalo, Taquari and Barra Grande (Buzzetti 1998, Mendonça and Gonzaga 1999, E. Mendonça and L. P. Gonzaga in litt. 2000). The species has been recorded in a range of habitats including the lush understorey of modified restinga, early successional habitats such as second growth and the understorey of old second growth (Mendonça and Gonzaga 1998, Mendonça and Gonzaga 1999), and sometimes abandoned banana plantations reverting to secondary forest (E. Mendonça and L. P. Gonzaga in litt. 2000). The main threat to the species is development of the narrow coastal plain for tourism and beachside housing, which has been extensive and threatens the small remnant patches of suitable habitat (Tobias et al. 1993, Tobias & Williams 1996).

The species is currently listed as Endangered based on its small and declining range. However, in the Brazilian Red List assessment for birds (MMA 2014, CEMAVE 2018) the species is listed as Critically Endangered under criterion C2a(ii). The species’s population is estimated at <250 mature individuals with at least 90% of individuals in a single subpopulation. There is a continued population decline due to habitat loss. The species’s most recent assessment on the Brazilian Red List can be accessed here. Based on this information, we are undertaking a review of the species’s Red List Category. Our current data on the species’s conservation status will now be compared to all Red List Criteria:

Criterion A – The species’s generation length has recently been reassessed as 3.23 years (Bird et al. 2020)*. Therefore, reductions should be assessed over a period of ten years for the application of Criterion A.

We have no direct data on population trends. From 2009 to 2018, 323 ha of tree cover was lost within the species’s range, equivalent to a 3.9% decrease in tree cover over ten years (Global Forest Watch 2020). However, the species is tolerant of degraded habitat and occurs in scrubby habitats and secondary forest, so the population may not have declined at an equivalent rate, if at all. The population reduction over the last ten years is tentatively suspected to have been between 1-4%. In 2017, approximately 0.8% of forest within the range was lost within a single year (Global Forest Watch 2020). Extrapolating this rate over 10 years would equate to approximately 8%. Using this value as a maximum, the population is suspected to decline by 1-8% over the next decade. In 2017-2018, approximately 1.5% of forest within the range was lost over two years (Global Forest Watch 2020). Extrapolating this rate over 10 years would equate to approximately 7%. Using this value as a maximum, the population is suspected to decline by 1-7% over ten years from 2017. Based on these figures, the species would qualify as Least Concern under Criterion A.

Criterion B – Based on the area of a Minimum Convex Polygon around the species’s mapped range (now updated to reflect recent records), the Extent of Occurrence (EOO) is estimated to be 410 km2. The Area of Occupancy (AOO) has not previously been quantified, but based on a 4 km2 grid placed over the area of mapped range, must be smaller than 312 km2. The EOO and AOO both meet the initial thresholds for listing as Endangered under Criterion B1 and B2. To list the species as threatened on the Red List under Criterion B, two of conditions a-c must also be met.

According to the Red List Guidelines, ‘a taxon can be considered to be severely fragmented if most (>50%) of its total area of occupancy is in habitat patches that are (1) smaller than would be required to support a viable population, and (2) separated from other habitat patches by a large distance.’ (IUCN Standards and Petitions Committee 2019). We do not have information to suggest that most of this species’s range is in patches that are too small to support viable populations. The species is therefore not considered here to be severely fragmented.

According to the Red List Guidelines, ‘The term ‘location’ defines a geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals of the taxon present. The size of the location depends on the area covered by the threatening event and may include part of one or many subpopulations.’ (IUCN Standards and Petitions Committee 2019). This species occurs in seven small and separate sites and the main threat is habitat loss. The number of locations is therefore determined by the area over which the population will be eliminated or severely reduced within three years. Although the species occurs at only seven sites, the number of locations may be larger if the population at one or more of these would not reasonably be expected to be eliminated or severely reduced by habitat loss within three years. Seven locations would meet condition (a) at the level of Vulnerable, but if there are more than 10 locations then condition (a) may only be approached, and not met.

According to the Brazilian Red List (CEMAVE 2018), the population is declining owing to ongoing habitat loss. If this is the case, then condition (b) would be met. However, the basis for this information is not provided. Remote-sensed data indicates that from 2009 to 2018, 323 ha of tree cover was lost within the range, equivalent to a 3.9% decrease in tree cover over ten years (Global Forest Watch 2020). However, the species is tolerant of degraded habitat and occurs in scrubby habitats and secondary forest, so the population may not have declined at an equivalent rate. If there is evidence that the species’s habitat is continuing to decline, then condition (b) would be met. There is no evidence to suggest that the species is undergoing extreme fluctuations, so condition (c) is not met.

To summarise, the species’s EOO and AOO both fall beneath the thresholds for listing the species as Endangered under Criterion B, but the species could qualify as Endangered, Vulnerable or Near Threatened under this criterion, depending on whether the population is severely fragmented, the number of locations and whether there is evidence for a continuing decline.

Criterion C – Black-hooded Antwren has an extremely small range, and it has been reported to be difficult to locate (Tobias et al. 1993, Tobias and Williams 1996), although it is considered locally abundant in suitable habitat (CEMAVE 2018). Reported densities are 156 pairs/km2 at Vale do Mambucaba and 89 pairs/km2 at Ariró (Gonzaga 2008). The population has previously been estimated to number 1,000-2,499 individuals based on an assessment of known records, descriptions of abundance and range size. Following revision of the range map, and assuming a lower proportion of the mapped range (11%) may be occupied, the population has been re-estimated at 475-5,178 individuals. This based on an assumed minimum population density of 40 individuals/km2 and an upper density of 178 individuals/km2, and assumes that 11-45% of the mapped range is occupied. This equates to approximately 317-3,452 mature individuals, here rounded to 300-3,500 mature individuals. If this figure is correct, the population size may fall beneath the threshold for Endangered under Criterion C.

The most recent Brazilian Red List states that the species is estimated to have fewer than 250 mature individuals (CEMAVE 2018), but no derivation of this estimate is provided. If this figure is correct, the population size falls beneath the threshold for Critically Endangered under Criterion C.

To list the species as threatened on the Red List under Criterion C further conditions must also be met though. As stated under Criterion B, it is not clear whether a continuing decline in population size can be inferred. We do not have population data from which to estimate the rate of decline, so the species cannot be assessed as threatened under Criterion C1. If the Vale do Mambucaba and Ariró populations comprise a single subpopulation, as implied in the Brazilian Red List (CEMAVE 2018), the species may have up to six subpopulations. The Brazilian Red List also states that at least 90% of mature individuals are found in a single subpopulation. If this is true, then the largest subpopulation may meet condition a(i) at the level of Endangered or Vulnerable, depending on the true total population size. It would also meet condition a(ii) at the level of Critically Endangered, but not at the levels of Endangered or Vulnerable.

In order to determine the appropriate category under Criterion C, it is necessary to determine the correct population size, the proportion of mature individuals in the largest subpopulation, and whether a continuing decline in population size can be inferred.

Criterion D– Based on the population estimates described above, the species may qualify as Endangered, Vulnerable or Near Threatened, depending on where the true population size is most likely to fall.

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.

To allow us to achieve a clearer assessment of the species’s status, we request the following information:

  • The species’s estimated population size, and the basis for this estimate.
  • The species’s subpopulation structure, and the number of mature individuals in the largest subpopulation.
  • Information on current rates of habitat loss within the species’s range and the likely proportion of the species’s range that could be affected within a period of three years.
  • Information on how habitat loss is likely to be impacting on the species’s population size.

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. 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. G., Symes, A., Taylor, J., Şekercioğlu, Ç. H. and Butchart, S. H. M. 2020. Generation lengths of the world’s birds and their implications for extinction risk. Conservation Biology online first view.

Buzzetti, D. R. C. 1998. Novos registros de Formicivora erythronotos (Formicariidae), com extensão de sua distribuição ao municipio de Parati.

Centro Nacional de Pesquisa e Conservação de Aves Silvestres (CEMAVE). 2018. Formicivora erythronotos Hartlaub, 1852. In: Instituto Chico Mendes de Conservação da Biodiversidade (ed.), Livro Vermelho da Fauna Brasileira Ameaçada de Extinção: Volume III – Aves, pp. 318-320. ICMBio, Brasília.

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

Gonzaga, L. P. 2008. Formicivora erythronotos Hartlaub, 1852. In: Machado, A. B. M.; Drummond, G. M.; Paglia, A. P. (ed.), Livro vermelho da fauna brasileira ameaçada de extinção, Volume 2, pp. 600-602. MMA and Fundação Biodiversitas, Brasília, DF and Belo Horizonte, MG, Brazil.

IUCN Standards and Petitions Committee. 2019. Guidelines for Using the IUCN Red List Categories and Criteria. Version 14. Prepared by the Standards and Petitions Committee. Downloadable from http://www.iucnredlist.org/documents/RedListGuidelines.pdf

Mendonça, E. C.; Gonzaga, L. P. 1998. Aspectos da biologia e conservaçao do papa-formigas-de-cabeça-negra Formicivora erythronotos (Thamnophilidae). VII Congresso Brasileira de Ornitologia, resumos, pp. 102. Sociedade Brasileira de Ornitologia, Brasilia.

Mendonça, E. C.; Gonzaga, L. P. 1999. Territory use by the Black-hooded Antwren, an endangered endemic species of southeastern Brazil. VI Congresso de Ornitologia Neotropical, libro de resúmenes (Fe de Erratas), pp. R.273. Sociedad de Ornitologia Neotropical, Monterrey y Saltillo, Mexico.

MMA. 2014. Lista Nacional Oficial de Espécies da Fauna Ameaçadas de Extinção. Portaria No 444, de 17 de dezembro de 2014. Diário Oficial da União – Seção 1. Nº 245, quinta-feira, 18 de dezembro de 2014.

Tobias, J. A.; Catsis, M. C.; Williams, R. S. R. 1993. Notes on scarce birds observed in southern and eastern Brazil: 24 July – 7 September 1993.

Tobias, J. A.; Williams, R. S. R. 1996. Threatened Formicivora antwrens of Rio de Janeiro state, Brazil. Cotinga: 62-66.

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3 Responses to Black-hooded Antwren (Formicivora erythronotos): request for information

  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, approximately 4% of tree cover was lost within the species’s range from 2009-2019 (Global Forest Watch 2020). This new information does not affect the suspected rates of population reduction.

  2. Red List Team (BirdLife International) says:

    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,
    BirdLife Red List Team

  3. Red List Team (BirdLife International) says:

    Preliminary proposal

    Based on available information, our preliminary proposal for the 2020 Red List would be to list Black-hooded Antwren as Endangered under Criterion B1ab(iii)+2ab(iii).

    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 the initial proposal.

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

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