Plumbeous Antvireo (Dysithamnus plumbeus): uplist from Vulnerable to Endangered?

This discussion was first published as part of the 2016 Red List update. At the time a decision regarding its status was pended, but to enable potential reassessment of this species as part of the 2021 Red List update this post remains open and the date of posting has been updated.

BirdLife species factsheet for Plumbeous Antvireo

Plumbeous Antvireo is restricted to south-east Brazil from Bahia to Rio de Janeiro. It is listed as Vulnerable under A2c+3c+4c; B1ab(i,ii,iii,iv,v); C2a(i). The population is estimated to number 2,500-9,999 mature individuals based on an assessment of known records, descriptions of abundance and range size. The population is suspected to be declining rapidly, in line with rates of habitat loss within its range. The fragmentation of the species’s range by extensive forest clearance has been and remains the one significant threat. It is now primarily restricted to a small number of protected areas, several of which remain to be consolidated, and from where recorded numbers are low.

In the Brazilian Red List assessment for birds (MMA 2014) the species was listed as Endangered under criterion B2ab(ii,iii). The species’s Area of Occupancy (AOO) has been estimated at less than 500 km2. The population is estimated to be severely fragmented with a continuing decline in AOO and habitat quality owing to timber and fuelwood harvesting in parts of the range. The species’s assessment on the Brazilian Red List can be accessed here.

The AOO is analogous to the area of suitable habitat occupied by the species, and for most taxa it is measured using 2 × 2 km grid cells. Further detailed information on this species’s geographic range, particularly its AOO is requested in order to clarify whether it merits uplisting to Endangered under criterion B2ab(ii,iii). The species’s range in southern Bahia may be more extensive than recorded as some large forest remnants remain to be surveyed thus any information from this part of the species’s range would be welcomed.

Comments are invited on the potential uplisting of this species to Endangered and further information is requested on the geographic range.

References:

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.

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11 Responses to Plumbeous Antvireo (Dysithamnus plumbeus): uplist from Vulnerable to Endangered?

  1. James Westrip (BirdLife) says:

    Based on available information, our proposal for the 2016 Red List would be to pend the decision on this species and keep this discussion open until 2017, while leaving the current Red List category unchanged in the 2016 update.

    Final 2016 Red List categories will be published on the BirdLife and IUCN websites in early December, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  2. Hannah Wheatley (BirdLife) says:

    Preliminary proposals

    Based on available information, our proposal for the 2017 Red List would be to pend the decision on this species and keep this discussion open until 2018, while leaving the current Red List category unchanged in the 2017 update.

    Final 2017 Red List categories will be published on the BirdLife and IUCN websites in early December, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  3. Claudia Hermes (BirdLife International) says:

    Based on available information, our proposal for the 2018 Red List would be to pend the decision on this species and keep this discussion open until 2019, while leaving the current Red List category unchanged in the 2018 update.
    Final 2018 Red List categories will be published on the BirdLife and IUCN websites in November, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  4. Hannah Wheatley (BirdLife) says:

    Preliminary proposal
    Based on available information, our preliminary proposal for the 2019 Red List would be to retain Plumbeous Antvireo (Dysithamnus plumbeus) as Vulnerable under Criterion C2a(i) .

    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.

  5. 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.

  6. Red List Team (BirdLife International) says:

    As stated above, this proposal was first posted in 2016. Since then, further information has been gathered and the species has been reassessed. The new assessment is as follows:

    Criterion A:

    The species’s generation length has been re-estimated, at 3.01 years, according to the methods presented in Bird et al. (2020). Hence reductions are here assessed over a period of ten years.

    Remote-sensed data on tree cover loss indicates that over ten years from 2009 to 2019, approximately 10% of tree cover with at least 50% canopy cover was lost within the species’s range (Global Forest Watch 2020).

    Extrapolating to 2020, over the past ten years, approximately 10% of tree cover with at least 50% canopy cover is estimated to have been lost within the species’s range. Since the species has a strong preference for primary forest, it is suspected to have undergone a population reduction of up to 10% over the past ten years.

    Based on the average rate of forest loss over the past four years, approximately 11% of tree cover is suspected to be lost within the species’s range over the next ten years. The species’s population is therefore suspected to undergo a reduction of up to 11% over the next ten years.

    These magnitudes of population reduction do not approach the thresholds for Vulnerable under Criterion A, so the species is assessed as Least Concern under this criterion.

    Criterion B:
    The species’s extent of occurrence, inferred from the area of a single minimum convex polygon around the species’s range, is 178,000 km2. This is far too big to approach the threshold for listing as threatened under Criterion B1, so the species is assessed as Least Concern under this criterion.

    The species’s area of occupancy (AOO) is not known. In the 2018 Brazilian Red List (de Lima Silva et al. 2018), the species’s AOO is estimated to be 48km2, based on the area of a 2km by 2km grid intersecting the point locations at which the species has been recorded. However, an AOO based solely on point records is likely to be an under-estimate, since the species is also likely to occur in the habitat surrounding these points. For this reason, this AOO value is not used in this assessment, and the species cannot be assessed under Criterion B2.

    For a species to qualify as threatened under Criterion B, two conditions must also be met. The species is not considered to be severely fragmented, since it is not the case that 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. The number of locations, defined as a ‘geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals of the taxon present’, is not known, but the main threats are logging and conversion to agriculture. Since these events affect only a small proportion of the total range, the number of locations is likely to be more than ten. Condition (a) is therefore unlikely to be met. Remote-sensed data on tree cover loss indicates that there is a continuing decline in the extent and quality of habitat, and declines in population size and AOO are also likely, so condition (b) is met. The species is not known to be undergoing extreme fluctuations, so condition (c) is not met. If only one condition is met, the species cannot qualify as threatened under Criterion B. The species is assessed as Least Concern under this Criterion.

    Criterion C:
    The species’s population size is poorly-known. It is generally considered uncommon and local, and appears to be common at very few sites. A study in the Rio Doce State Park found that it was 69% less abundant in an area of secondary forest than in an area of primary forest (Loures-Ribeiro et al. 2011).

    Based on the total areas of tree cover within the species’s range with at least 75% and 50% tree cover in 2010 (16,600 km2, 20,700 km2; Global Forest Watch 2020), the first quartile and median recorded population densities for other species in the same family (6.6 and 18 individuals/km2; Santini et al. 2018), and assuming the density in the area with 50% canopy cover is a third of that found in the area with 75% canopy cover, and that 10-25% of the area of tree cover is occupied, the species’s population size can be calculated to fall within the range 11,849 – 33,478 individuals, roughly equating to 7,899 – 22,319 mature individuals, rounded here to 7,000 – 23,000 mature individuals. This range of values could qualify the species as Vulnerable, Near Threatened or Least Concern. Given that the species is apparently uncommon (de Lima Silva et al. 2018) and prefers undisturbed, primary forest (Zimmer & Isler 2019), the true population size is suspected to be nearer the lower end of this range.

    Remote-sensed data on tree cover loss indicates that over ten years from 2009 to 2019, approximately 10% of tree cover with at least 50% canopy cover was lost within the species’s range (Global Forest Watch 2020). The species prefers undisturbed forest and is therefore inferred to be declining.

    Although the number of subpopulations is not known, the remaining primary forest within the species’s habitat is highly fragmented, so it is suspected that the largest subpopulation may have fewer than 1,000 mature individuals.

    Based on this information, the species may qualify as Vulnerable, Near Threatened or Least Concern under this Criterion.

    Criterion D: Based on the population size estimate described above, the population size is too large to meet the thresholds for Criterion D, and the species is assessed as Least Concern under this criterion.

    Overall assessment:
    Based on the above assessment it is proposed to precautionarily retain the species as Vulnerable under Criterion C2a(i). However, if further evidence suggests that the population size is likely to be larger than 10,000 mature individuals, the species may be downlisted. Conversely, if further evidence suggests that the AOO is indeed smaller than 500km2, AND that the species is either severely fragmented (sensu IUCN Standards and Petitions Committee 2019, or has no more than ten locations (sensu IUCN Standards and Petitions Committee 2019), the species may be uplisted to Endangered under Criterion B2.

    Comments are welcome on this proposed listing. Further information is particularly requested on the species’s population size and subpopulation structure, and on the area of occupied habitat. Maps of the species’s occupied range would be welcomed, and should be emailed to redlistteam@birdlife.org. Thank you.

    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 in prep.

    de Lima Silva, S. B., Custódio Leal, D. & Pinto Marques, F. 2018. Dysithamnus plumbeus (Bornschein, Reinert & Teixeira, 1995). In: Instituto Chico Mendes de Conservação da Biodiversidade (ed.), Livro Vermelho da Fauna Brasileira Ameaçada de Extinção: Volume III – Aves, ICMBio, Brasília.

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

    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.

    Loures-Ribeiro, A., Manhães, M.A. and Dias, M.M. 2011. Sensitivity of understorey bird species in two different successional stages of the lowland Atlantic Forest, Brazil. Anais da Academia Brasileira de Ciências 83(3): 973-980.

    Santini, L.; Isaac, N. J. B.; Ficetola, G. F. 2018. TetraDENSITY: A database of population density estimates in terrestrial vertebrates. Global Ecology and Biogeography 27: 787-791.

    Zimmer, K. & Isler, M.L. 2019. Plumbeous Antvireo (Dysithamnus plumbeus). Barcelona

  7. Diego Lima says:

    The National (Brazilian) assessment verified the IUCN criteria and classified the species as Endangered (EN) B2ab (ii, iii). The assessment was carried out in 2019 and was composed by the following team of researchers: Ciro Ginez Albano, Glayson Ariel Bencke, José Fernando Pacheco, Luís Fábio Silveira, Vítor de Queiroz Piacentini and Wagner Nogueira Alves.

    It is endemic to Brazil, occurring from the south of Bahia and Espírito Santo to the east of Minas Gerais and the far north of Rio de Janeiro (Zimmer & Isler, 2003). The occupation area (AOO) of D. plumbeus was calculated by superimposing a grid with 4 km2 squares to the recent registration points, adding the area of ​​the squares for which the species occurs. Thus, AOO was calculated at 144 km2.

    It is highly sensitive to environmental degradation due to its great habitat specificity. There are obvious threats due to habitat loss and fragmentation due to the removal of wood and firewood in the state of Bahia and Espírito Santo, causing population decline. The population is severely fragmented and individuals do not move long distances outside their habitat. Brazilian researchers have made intensive efforts in the area of ​​distribution of the species and can affirm that the records are not underestimated. On the contrary, the species has been less and less common in its main area of ​​occurrence the Sooretama Biological Reserve.

  8. 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

  9. Red List Team (BirdLife International) says:

    Preliminary proposal

    Thank you for the comment on this proposed listing. In response, we have made further refinements to the species’s distribution map and consequently revised some of the information in this species’s assessments. We have reduced the map to include only patches of forest around recent records sourced from eBird and WikiAves. We omitted some isolated records that did not appear to have been recorded within intact forest habitat. The updated range map will be published alongside the new assessment, in December 2020 or January 2021.

    Criterion A: Extrapolating to 2020, over the past ten years, approximately 10% of tree cover with at least 50% canopy cover is estimated to have been lost within the species’s range (Global Forest Watch 2020). Since the species has a strong preference for primary forest, it is inferred to be declining, having undergone a population reduction of up to 10% over the past ten years. Based on the average rate of forest loss over the past four years, approximately 12% of tree cover is suspected to be lost within the species’s range over the next ten years. The species’s population is therefore suspected to undergo a reduction of up to 12% over the next ten years.

    Criterion B: The updated EOO was found to be 140,000 sqkm. Based on the total area of a 4 sqkm grid intersecting the revised distribution map, the AOO was estimated at 6,820 sqkm. We acknowledge that a smaller AOO of 144 sqkm has been derived for the Brazilian national assessment. However, we consider that an AOO based solely on recent point records is likely to be an under-estimate, since the species can also be inferred to occur in the habitat surrounding these points. Both the habitat and the species’s distribution are highly fragmented as a result of substantial forest loss. However, 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). Whilst part (2) of this definition is met, we do not have evidence that part (1) is met.

    Criterion C: Based on the total areas of tree cover within the species’s revised range map with at least 75% and 50% tree cover in 2010 (2,770 sqkm, 3,160 sqkm; Global Forest Watch 2020), the first quartile and median recorded population densities for other species in the same family (6.6 and 18 individuals/sqkm; Santini et al. 2018), and assuming the density in the area with 50% canopy cover is a third of that found in the area with 75% canopy cover, and that 25-40% of the area of tree cover is occupied, the species’s population size is suspected to fall within the range 4,785 – 20,880 individuals, roughly equating to 3,190 – 13,920 mature individuals, rounded here to 3,000 – 14,000 mature individuals. Given the species’s fragmented range, it is also suspected that the largest subpopulation may have fewer than a thousand mature individuals. However, given the paucity of population data for this species, these estimates may not be robust enough to assess the species as threatened under Criterion C.

    Based on the information presented here, our preliminary proposal for the 2020 Red List would be to list Plumbeous Antvireo as Near Threatened, approaching the thresholds for Criteria B2ab(ii,iii,v); C2a(ii). We emphasize that there is a strong need for further research on this species’s area of occupied habitat and population size.

    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 or January 2021, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  10. Diego Lima says:

    So, we can only use AOO if we are really sure that the area was well sampled, detecting locations and subpopulations exhaustively. In the national assessment (researchers active in field work) they have the biological knowledge of the species, which presents specificity to the habitat. We do not put overlapping squares (2 x 2 km) in areas that we are sure do not have the species, even though through satellite images they notice that there is a fragment apparently good for the species. However, fieldwork reveals that such fragments do not have adequate micro-habitat. Dysithamnus plumbeus is not an enigmatic species, the present vocal repertoire known by ornithologists is not difficult to identify and there are few people able to identify it. It is a conspicuous species that occurs in a well-sampled area and for this reason supposes that the majority of occurrences have been detected, which allows to use AOO calmly with a grid overlapping the current record points. Thus, D. plumbeus was assessed nationally as Em Perigo (EN) B2ab (ii, iii).

  11. Red List Team (BirdLife International) says:

    Recommended categorisation to be put forward to IUCN

    Thank you for the helpful comments on this proposal. Based on available information, our proposal for the 2020 Red List is to pend the decision on this species and keep the discussion open until 2021, while leaving the current Red List category unchanged in the 2020 update.

    We acknowledge that a smaller AOO of 144 sqkm has been derived for the Brazilian national assessment, by intersecting recent point records with a 4 sqkm grid. According to the Red List Guidelines, ‘For conspicuous taxa occurring in well-sampled areas, it may be reasonable to assume that most occurrences have been detected and AOO may be estimated by tallying the area of 2 × 2 km grid cells in which observation records are located…. For other taxa that may have many unrecorded occurrences, however, this assumption and the resulting tally will underestimate AOO.’ The range has been well-sampled, and the species is not inconspicuous. However, the species is found over a wide area of Brazil, so there may be further unrecorded occurrences. It is not known what cut-off date was used for records to be included in the AOO produced for the Brazilian assessment. We would not usually base an assessment of AOO on recent records alone, unless there is reason to believe that the species has been extirpated from areas with older records (for example, because the habitat has been cleared in those areas). Furthermore, a species’s presence can generally be inferred in the area of contiguous habitat around a point record, and the Brazilian assessment has not attempted to map this area. We have updated our range map for this species, to include only areas of forest, or protected areas, surrounding point records (map available by email on request), and used this map to generate an AOO of 6,820 sqkm. Although this is fairly crude, and it is unlikely that all of this area is occupied for the species, the resulting AOO figure is a long way above the thresholds for threatened under Criterion B2.

    Furthermore, a species cannot be listed under a threatened category under Criterion B2 based on Area of Occupancy alone. Two of conditions B2a-B2c must also be met. Based on remote-sensed data on forest loss, the species is inferred to have a continuing decline in population size and habitat extent, so condition B2b is met. There is no evidence that the species is undergoing extreme fluctuations, so condition B2c cannot be met. This means that for the species to qualify as threatened, it must also meet condition B2a.

    For the species to meet condition B2a, it must have no more than ten locations (or no more than five locations to qualify as Endangered), or it must be severely fragmented. Both of these terms have specific definitions in the context of Red List assessments.

    According to the Red List Guidelines, ‘the following criterion can be used to decide whether there is severe fragmentation in cases where data are available on (i) the distribution of area of occupancy (i.e., detailed maps of occupied habitat), (ii) some aspect of the dispersal ability of the taxon (e.g., average dispersal distance), and (iii) average population density in occupied habitat (e.g., information on territory size, home range size, etc.). Then: 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.
    For (1), the area for a viable population should be based on rudimentary estimates of population density, and on the ecology of the taxon. For example, for many vertebrates, subpopulations of fewer than 100 individuals may be considered too small to be viable.
    ’ (IUCN Standards and Petitions Committee 2019).

    Although the Plumbeous Antvireo’s range is certainly fragmented, we do not currently have evidence to suggest that >50% of its total area of occupancy is in habitat patches that are smaller than would be required to support a viable population (e.g. support <100 individuals).
    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. 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).
    The main threat affecting the Plumbeous Antvireo is forest loss, largely through conversion to agriculture. This means that a ‘location’ should be defined as the area affected by a single forest clearance event. Based on the distribution of records and the inferred area of occupancy around these records, it is inferred that there are more than ten locations (although potentially not many more).

    Given the large discrepancy between the Brazilian assessment of the species’s AOO and the AOO inferred from our updated map, and the uncertainty around whether the species is severely fragmented (and hence whether condition B2a is met), we propose to pend the decision on this species until 2021, to allow more time to evaluate the evidence and for these important points to be resolved.

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