Parana Antwren (Formicivora acutirostris): request for information.

BirdLife species factsheet for Parana Antwren

The Parana Antwren (Formicivora acutirostris) is found in a range of littoral marsh habitats in Paraná, Santa Catarina and Rio Grande do Sul, southern Brazil. It was found in 1995 in a small marsh near Matinhos city, southern Paraná coast (Bornschein et al. 1995). Subsequent surveys have found the species at Antonina, Morretes, Paranaguá, Pontal do Paraná and Guaratuba municipalities in Paraná state, and at Garuva, Itapoá, Joinville, Araraquari, Balneário Barra do Sul, Guaramirim, São João do Itaperiú, Barra Velha, Laguna and Paulo Lopes municipalities in Santa Catarina state (Bornschein and Reinert 1997, Reinert 2001, Reinert et al. 2007, WikiAves 2019). The species has also been recorded in the municipality of Dom Pedro de Alcântara in Rio Grande do Sul (Bencke et al. 2010).

The species is currently listed as Endangered under Criterion B1. However, a recalculation of the species’s extent of occurrence (EOO) based on a minimum convex polygon (IUCN 2017) means that the species no longer qualifies for listing as Endangered under this criterion. Hence, we are undertaking a review of the species’s Red List Category.

Our current information on the species’s conservation status will now be compared to all Red List Criteria.

Criterion A – We have no direct data on population trends. A study of the area of suitable habitat within the species’s range estimated that it had decreased by 9.5% between 1978-80 and 2013 (Bornschein 2013), which is equivalent to a reduction of approximately 4% across three generations (14.4 years). This does not approach the thresholds for listing the species as threatened under Criterion A. We do not have evidence to suggest that the population has declined at a faster rate, or that it will do so over the next three generations. The species is therefore assessed as Least Concern under Criterion A.

Criterion B – The species’s extent of occurrence (EOO) is estimated at 27,900 km2. This does not meet the threshold for listing the species as threatened under Criterion B1. The species’s area of occupancy (AOO) has been estimated at 54.8 km2 (Bornschein 2013) and the species is listed as Endangered under Criterion B2 on the Brazilian list of threatened species (MMA 2014). However, according to IUCN Guidelines (IUCN 2017), a species’s AOO should be measured at the scale of 2 km by 2 km grid cells, so we are unable to use this AOO estimate to assess the species’s status under Criterion B2. By placing a 2 km by 2 km grid over our range map for the species, we obtain an estimate of the maximum possible AOO of 2,020 km2. The true AOO is likely to be smaller than this, as the mapped range contains areas of suitable habitat, so it is likely to at least meet the threshold for listing the species as Vulnerable under Criterion B2. However, to list the species as threatened on the Red List under Criterion B, two of conditions a-c must also be met.

According to IUCN Guidelines (IUCN 2017), ‘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’. Three of the species’s subpopulations have been estimated to number more than 1,000 mature individuals (Bornschein 2013), and the great majority of the species’s range is concentrated in coastal Parana and northeast Santa Catarina, without large gaps between subpopulations. We therefore do not consider the species to be severely fragmented according to the IUCN definition.

IUCN Guidelines (2017) state that ‘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. Where a taxon is affected by more than one threatening event, location should be defined by considering the most serious plausible threat.

The most significant threat to this species is considered to be encroachment of invasive plant species (Reinert et al. 2007, Bornschein 2013), and habitat was estimated to have been lost at a rate equivalent to around 4% across three generations (Bornschein 2013). If we assess the number of locations based on the threat of invasive plants, the species is unlikely to have ten or fewer locations and hence condition a is not met. However, if there is another more serious plausible future threat that could result in a larger proportion of the species’s range being affected in a short period of time, then the species could have a smaller number of locations. For example, if fire or a development could plausibly destroy one of the species’s subpopulations in a short time, then that subpopulation may be considered to be a single location and the total number of location may be closer to, or smaller than ten, thereby meeting condition a at the level of Near Threatened or Vulnerable. A decline has been estimated in the species’s area and quality of habitat (Bornschein 2013), and from this we can infer that the species is also undergoing a continuing decline in number of mature individuals. Condition b is met. There is no evidence that the species’s population or range size are undergoing extreme fluctuations. Condition c is not met.

The species’s AOO likely falls beneath the threshold for listing the species as Vulnerable and possibly Endangered under Criterion B2, and condition b is met, but it is unclear whether condition a is also met.  Depending on the number of locations, the species could qualify for any category from Endangered to Near Threatened, or even Least Concern.

Criterion C – The species’s population size was previously estimated at 17,700 mature individuals (Reinert et al. 2007), but a more recent study estimated the population at 7,511 mature individuals, based on recorded population densities and estimated areas of a range of habitats (Bornschein 2013). The species, therefore, meets the population size threshold for listing as Vulnerable under Criterion C. However, to list the species as threatened on the Red List under Criterion C further conditions must also be met.

A continuing decline in population size can be inferred from the estimated reduction in the area of occupied habitat (Bornschein 2013). We do not have direct population data from which to estimate the rate of population decline, and suspected declines don’t approach the threshold for Vulnerable anyway, so the species does not warrant listing under Criterion C1.

The species was considered to have eight subpopulations in Parana and Santa Catarina (Reinert et al. 2007), with a further locality discovered in Rio Grande do Sul. The largest subpopulation has been estimated to comprise 2,762 mature individuals, with an additional two subpopulations holding more than 1,000 mature individuals each (Bornschein et al. 2013). From this information, we can conclude that the species does not meet conditions 2a(i) or 2a(ii). There is no evidence that the species’s population size is undergoing extreme fluctuations so the species doesn’t meet condition 2b.

Although the species’s population size is likely to fall beneath the threshold for listing the species as threatened under Criterion C, and the species’s population is declining, none of conditions 2a(i), 2a(ii) or 2b are met. The species therefore qualifies as Least Concern under Criterion C.

Criterion D – Based on the population estimate of 7,511 mature individuals, the species’s population size does not meet or approach the threshold for Vulnerable under Criterion D. The species does not have a restricted area of occupancy or number of locations such that a plausible future threat could drive the species to Critically Endangered or Extinct within a very short time. The species does not therefore meet the criteria for listing as Vulnerable under Criterion D2. The species is therefore assessed as Least Concern under Criterion D.

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, further information is requested on this species’s conservation status. In particular, we request information on the threats which may affect this species and their likely effects and areas of impact.

We would also welcome a further assessment of the species’s AOO, measured at the scale of 2 km by 2 km grid squares, or a GIS file of the species’s occupied habitat that we could use to calculate AOO at this scale. Please send any GIS files by email to

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.

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.


Bencke, G. A., Dias, R. A., Bugoni, L., Agne, C. E., Fontana, C. S., Maurício, G. N. and Machado, D. B. (2010) Revision and updating of the list of birds of Rio Grande do Sul, Brazil. Iheringia, Sér. Zool. 100(4): 519–556.

Bornschein, M. R. (2013) Biologia da conservação do Bicudinho-do-brejo Stymphalornis acutitrostris (aves, Thamnophilidae). (Unpublished doctoral thesis). Universidade Federal do Paraná, Curitiba.

Bornschein, M. R. and Reinert, B. L. (1997) Novas informaçãoes sobre a distribuição e habitat de Stymphalornis acutirostris (Formicariidae). Resumos VI Congresso Brasiliero de Ornitologia, Belo Horizonte, 24-28 February 1997.

IUCN (2017) Guidelines for Using the IUCN Red List Categories and Criteria. Version 13 March 2017. Available at:

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.

Bornschein, M. R., Reinert, B. L. and Teixeira, D. M. (1995) Um novo formicariidae do sul do Brasil (Aves, Passeriformes).

Reinert, B. L. (2001) Universidade Federal do Paraná., Dissertação de mestrado. Curitiba.

Reinert, B. L., Bornschein, M. R., Firkowski, C. (2007) Distribuição, tamanho populacional, hábitat e conservação do bicudinho-do-brejo Stymphalornis acutirostris Bornschein, Reinert e Teixeira, 1995 (Thamnophilidae). Revista Brasileira de Ecologia 15(4): 493-519.

WikiAves (2019) Mapa de registros da espécie bicudinho-do-brejo (Formicivora acutirostris) Available at: (Accessed: 18/04/2019).

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1 Response to Parana Antwren (Formicivora acutirostris): request for information.

  1. Hannah Wheatley (BirdLife) says:

    Since we do not have evidence to suggest that the species has ten or fewer locations (see definition above), based on available information, our preliminary proposal for the 2019 Red List would be to list Parana Antwren (Formicivora acutirostris)
    as Near Threatened, approaching the thresholds for listing as threatened under Criterion B2ab.

    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 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.

Comments are closed.