Please note that this topic was edited on 3rd June to include the evidence provided by the newly-released Global Forest Change dataset (Hansen et al. 2013) of tree cover loss up to 2019. The recommended category has been changed as a result.
The Spix’s Antwarbler (Hypocnemis striata) is endemic to Brazil, where it occurs in the Amazon basin, in the states of Pará, Mato Grosso and Amazonas. Its range is bounded by the Roosevelt and lower Madeira rivers to the west, the Amazon river to the north and the Tocantins river to the East (Isler et al. 2007, del Hoyo et al. 2020). It occurs in the understorey to midstorey of humid evergreen-forest borders (terra firme, transitional and seasonally flooded areas), especially in densely vegetated light-gaps (e.g., around treefalls) and streams within forest, as well as adjacent tall second-growth woodland (del Hoyo et al. 2020).
The species is threatened by forest loss and disturbance, largely resulting from agriculture, grazing and selective logging. Forest loss has been extensive in Pará and Mato Grosso (INPE 2019, Global Forest Watch 2020). A study has indicated that the disturbance from fire and logging can double the biodiversity loss caused by deforestation (Barlow 2016); however, the species is thought to be tolerant of forest areas that have survived fire (del Hoyo et al. 2020).
The species is currently listed as Least Concern. Clear-cut deforestation in Amazonian Brazil has increased over recent years (INPE 2019). 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 – Remote-sensed data indicates a loss of approximately 7% of tree cover with at least 30% canopy cover within the species’s range from 2009-2019 (Global Forest Watch 2020).
An analysis of the impact of disturbance on forest species in Pará found that in private lands or sustainable-use reserves, the impact of disturbance on biodiversity was equivalent to that of an additional 51% loss of forest, with disturbance in areas with 83% forest loss causing 147% the expected level of biodiversity loss (Barlow et al. 2016). However, Spix’s Antwarbler is thought to be tolerant of forest that has survived fire (del Hoyo et al. 2020).
Assuming that the population size is proportional to tree cover area, and taking into account the potential additional impact of disturbance, the population size is suspected to have undergone a reduction of 7-17% over the past decade (one generation length has been calculated at 2.7 years; Bird et al. 2020*). The species is assessed as Least Concern under Criterion A2.
In the three years from 2017-2019, approximately 2.8% of tree cover within the species’s range was lost (Global Forest Watch 2020). If this rate of forest loss were to occur over ten years, this would equate to a loss of 9%.
Data on areas of clear-cut deforestation in the legal Amazon found a 40.7% increase from 2018-2019 in Pará (INPE 2019). However, finer-scale data on tree cover loss from Global Forest Watch indicated that the area of tree cover loss within the species’s range was very similar in 2019 to that in 2018 (Global Forest Watch 2020).
Assuming that the population size is proportional to tree cover area, and that disturbance may increase the impact of deforestation by up to 147%, a population reduction of 7-22% is suspected over the next decade. Taking 51% as a best estimate of the additional impact of disturbance and assuming 9% forest loss, the best estimate of population reduction over the next decade is 14%. The range of estimates could qualify the species for Least Concern or Near Threatened under Criteria A3 and A4 (assuming the same average rates of decline apply over 2017-2029). The best estimate approaches does not approach the threshold for Vulnerable. Therefore, it is suggested that the most appropriate category for Spix’s Antwarbler under Criterion A is Least Concern.
Criterion B – Inferred from the area of a minimum convex polygon around the mapped range, the Extent of Occurrence (EOO) is estimated at 1,190,000 km2. This does not approach the threshold for listing as threatened under Criterion B1. The Area of Occupancy (AOO) has not been quantified, but is unlikely to be smaller than 2,000 km2. Spix’s Antwarbler is therefore assessed as Least Concern under Criterion B.
Criterion C – The species is described as fairly common to common throughout most of its extensive range, although it is apparently uncommon and very local at the eastern edge of its range (del Hoyo et al. 2003). Based on the area of tree cover within the range (Global Forest Watch 2020), the minimum and median recorded densities of congeners (2-33 individuals per km2; Thiollay 1986, Terbough et al. 1990) and assuming that 25-40% of habitat within the range is occupied, the population size is tentatively suspected to fall within the range 437,000-699,000 individuals, roughly equating to 291,000-466,000 mature individuals and here placed in the band 100,000-499,999 mature individuals. This does not approach the threshold for listing as threatened under Criterion C. Spix’s Antwarbler is assessed as Least Concern under this criterion.
Criterion D – Based on the population described above, the population size does not meet or approach the threshold for Vulnerable under Criterion D. The species does not have a restricted AOO of number of locations such that deforestation could drive it to Critically Endangered or Extinct within a very short time. Spix’s Antwarbler does therefore not meet the criteria for listing as Vulnerable under Criterion D2, and it is 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.
Based on the above assessment, it is proposed to retain the Spix’s Antwarbler (Hypocnemis striata) as Least Concern. We welcome any comments to the proposed listing. Information is particularly requested on:
- the proportion of forest that is likely to be lost within the species’s range over the next decade
- the impact of disturbance on the species
- the degree to which both deforestation and disturbance are likely to impact 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. 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.
Barlow, J., Lennox, G. D., Ferreira, J., Berenguer, E., Lees, A. C., Mac Nally, R., Thomson, J. R., de Barros Ferraz, S. F., Louzada, J., Oliveira, V. H. F. and Parry, L. 2016. Anthropogenic disturbance in tropical forests can double biodiversity loss from deforestation. Nature 535(7610): 144-147.
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.
del Hoyo, J., N. Collar, and G. M. Kirwan. 2020. Spix’s Warbling-Antbird (Hypocnemis striata), version 1.0. Ithaca, NY, USA Available at: https://birdsoftheworld.org/bow/species/spiwaa1/cur/introduction. (Accessed: 15 May 2020).
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INPE. 2019. A estimativa da taxa de desmatamento por corte raso para a Amazônia Legal em 2019 é de 9.762 km². São José dos Campos-SP Available at: http://www.inpe.br/noticias/noticia.php?Cod_Noticia=5294. (Accessed: 25 March 2020).
Isler, M. L., Isler, P. R. and Whitney, B. M. 2007. Species limits in antbirds (Thamnophilidae): the Warbling Antbird (Hypocnemis cantator) complex. The Auk 24(1): 11-28.
Terborgh, J., Robinson, S. K., Parker, T. A., Munn, C. A. and Pierpont, N. 1990. Structure and organization of an Amazonian Forest bird community. Ecological Monographs 60(213-238).
Thiollay, J. M. 1986. Structure comparee du peuplement avien dans trois sites de foret primaire en Guyane. Revue d’Ecologie (La Terre et la Vie) 41: 59-105.