Archived 2019 topic: The newly described taxon Cordillera Azul Antbird (Myrmoderus eowilsoni) is to be recognized as a species by BirdLife International

Cordillera Azul Antbird (Myrmoderus eowilsoni) has been discovered in 2016 near Flor de Café in the western Cordillera Azul of the Peruvian Andes. Based on its vocalisation and on genetic and morphological analysis, the species was described as a new taxon in 2018 (Moncrieff et al. 2018).

Currently, Cordillera Azul Antbird is only known from the mountain ridge around the type locality between c. 1,300 and 1,700 m. However, it seems to be highly likely that the species has a wider distribution, encompassing further ridges in the Cordillera Azul and possibly also the Cordillera El Sira (Moncrieff et al. 2018). The authors assume that a large part of the population occurs in the Cordillera Azul National Park (Moncrieff et al. 2018).

The species inhabits tall, humid, montane forest with a dense vegetation cover in the understory. It seems to avoid secondary forest, edges and treefall gaps, but has been recorded in close proximity to large plantations (Moncrieff et al. 2018). Cordillera Azul Antbird keeps close to the ground and moves by walking or short, low flights (Moncrieff et al. 2018). The species is territorial; territories have been tentatively estimated at 0.25 km2 (Moncrieff et al. 2018).

Cordillera Azul Antbird was found to be fairly common in fragments of intact forest (Moncrieff et al. 2018). Based on the mean territory size of this species and the closely related Ferruginous-backed Antbird Mymoderus ferrugineus (Johnson et al. 2011), an estimate of habitat occupancy for Ferruginous-backed Antbird (Stouffer 2007) and the availability of suitable habitat, the authors produced a preliminary population estimate (Moncrieff et al. 2018): The Cordillera Azul National Park includes 1,940 km2 of forest between 1,300 and 1,700 m; hence the population of Cordillera Azul Antbird in the National Park may consist of 7,000-27,000 mature individuals. Including areas outside of the park in the right elevation throughout the entire cordillera increases the estimate to 9,000-34,000 mature individuals. Therefore, until more detailed information becomes available, we can place the population in the band 7,000-34,000 mature individuals.

The major threat to the forests around the type locality is the extensive, large-scale clear-cutting for conversion into coffee plantations. Until now however, the Cordillera Azul National Park protects large tracts of intact forest (Moncrieff et al. 2018).

Here, we present our assessment against all criteria for this newly described species.

Criterion A – The population trend of Cordillera Azul Antbird has not been directly quantified. While forests within the Cordillera Azul National Park remain largely intact, forests outside of it are rapidly cleared. Based on this, we can infer that the species is undergoing a slow decline, however the overall rate of habitat loss within the species range does not approach the thresholds for listing as threatened (>30% in three generations or 10 years). In the absence of other significant threats to the species, the species would be considered to be Least Concern under Criterion A.   

Criterion B – Based on the assumption that the species occurs throughout the Cordillera de Azul, the Extent of Occurrence (EOO) has been calculated at 35,250 km2. This is too large to warrant listing as threatened under Criterion B1 (EOO < 20,000 km2). The maximum Area of Occupancy (AOO), as calculated from a 2 km by 2 km grid overlaid over the mapped range, is c. 25,000 km2. This is does not approach the threshold for listing as threatened under Criterion B2 (AOO < 2,000 km2). In case that the species will be found to occur in the Cordillera El Sira, the EOO will have to be corrected upwards accordingly. Overall, the species may be considered Least Concern under Criterion B.

Criterion C – The population size of this species is preliminarily estimated at 7,000-34,000 mature individuals. Assuming that the true population size is closer to the lower end of the estimate, this meets the threshold for listing as Vulnerable under Criterion C (< 10,000 mature individuals), but could also be assessed as Near Threatened to Least Concern. In order to be listed at Vulnerable under Criterion C, other conditions have to be met.

The rate of decline in the species has not been directly estimated, and so Criterion C1 cannot be used. Instead, using a conservative and precautionary approach, a population decline can be inferred from the rate of habitat loss at the type locality outside of the Cordillera Azul National Park. There is no information whether the species undergoes extreme fluctuations, and so it cannot be assessed against Criterion C2b. It thus depends on the species’s subpopulation structure whether it qualifies for listing as Vulnerable under condition (a). Currently, the species is only known from one locality. Therefore, we can assume that the species forms just one subpopulation, triggering condition a(ii). Unless new information becomes available, Cordillera Azul Antbird may be listed as Vulnerable under Criterion C2a(ii).

Criterion D – The population size and range of this species are too large to warrant listing under Criterion D. Therefore, Cordillera Azul Antbird may be considered Least Concern under this criterion.

Criterion E – To the best of our knowledge no quantitative analysis of extinction risk has been conducted for this species. Therefore, it cannot be assessed against this criterion.

The uncertainty over the population estimate requires a judgement on the most appropriate Red List category to use. In most cases, the precautionary principle is applied, which here would suggest that the assessment is based on the lower bound of the population estimate, and the species would hence be considered Vulnerable under C2a(ii). However, it is notable that the authors are ‘optimistic that the species will be found to be a common resident in other parts of the mountain range’ (Moncrieff et al. 2018), strongly hinting that they do not agree with this high level of caution.

Tentatively, it is proposed that Cordillera Azul Antbird (Myrmoderus eowilsoni) be listed as Vulnerable under Criterion C2a(ii). We welcome any comments on this proposed listing, particularly on whether the optimistic tone set by the paper describing the species is correct. Any further information on population size and distribution of the species are highly valued.

Please note that this topic is not designed to be a general discussion about the ecology of the species, rather a discussion of its Red List status. Therefore, please make sure your comments are relevant to the discussion outlined in the topic.

References

Johnson, E. I.; Stouffer, P. C.; Vargas, C. F. 2011. Diversity, biomass, and trophic structure of a central Amazonian rainforest bird community. Revista Brasileira de Ornitologia 19: 1-6.

Moncrieff, A. E.; Johnson, O.; Lane, D. F.; Beck, J. R.; Angulo, F.; Fagan, J. 2018. A new species of antbird (Passeriformes: Thamnophilidae) from the Cordillera Azul, San Martín, Peru. The Auk: Ornithological Advances 135: 114-126.

Stouffer, P. C. 2007. Density, territory size, and long-term spatial dynamics of a guild of terrestrial insectivorous birds near Manaus, Brazil. The Auk: Ornithological Advances 124: 291-306.

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4 Responses to Archived 2019 topic: The newly described taxon Cordillera Azul Antbird (Myrmoderus eowilsoni) is to be recognized as a species by BirdLife International

  1. Red List Team (BirdLife International) says:

    Preliminary proposal
    Based on available information, our preliminary proposal for the 2019 Red List would be to adopt the proposed classifications outlined in the initial forum discussion.
    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 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.

  2. Oscar Johnson says:

    We, Andre Moncrieff and Oscar Johnson, lead authors of the description of this species would like to address the BirdLife International proposal to elevate Myrmoderus eowilsoni to Vulnerable under the IUCN criterion C2a(ii). We fully recognize the importance of providing Red List status for deserving taxa, and also that “borderline” cases be decided using the precautionary principle. At the same time, we believe it undercuts the credibility of the Red List to overapply its criteria and prematurely include species for which inadequate data are available.

    The criterion C2a(ii) for Vulnerable status is met when “population size estimated to number fewer than 10,000 mature individuals and . . . all mature individuals are in one subpopulation”. Since the minimum in our most conservative estimate of population size (7,000-27,000 individuals) falls below 10,000, we agree that the species qualifies for Vulnerable status under the first part of C2a(ii). However, we believe it is a misinterpretation of our findings to apply the second part of C2a(ii) (“all mature individuals are in one subpopulation”) to Myrmoderus eowilsoni. Considering the vast, pristine, and protected habitat near the type locality, it seems far more reasonable to us to assume that multiple subpopulations of Myrmoderus eowilsoni reside in the region.

    The BirdLife proposal correctly states that Myrmoderus eowilsoni is only known from one locality (15 km2 using a minimum convex polygon of all known sites). However, the proposal further states “Therefore, we can assume that the species forms just one subpopulation, triggering condition a(ii).”We believe this assumption is unwarranted given the complete lack of surveys by ornithologists in appropriate habitat on the same ridge as the type locality (totaling ~78 km2). Furthermore, surveys are very few across the extensive and pristine habitat on ridges within the nearby Cordillera Azul National Park. We believe it is a mistake to assume absence when there is almost a complete lack of relevant data.

    We consider, as we suggest in our initial publication, that a Data Deficient status is most appropriate given the lack of data for this taxon. We do not believe this is a liberal application of the Data Deficient status, but rather that it appropriately highlights the great need for further surveys in the region.

    • Red List Team (BirdLife International) says:

      Thank you very much for your comment and for the additional information you provided. This is very helpful for the assessment of the species.
      In the following, please find a more detailed explanation of how BirdLife assessed the species, which will hopefully help to clarify the issues you raised.

      Application of the DD category
      Following IUCN guidelines (IUCN 2012), a taxon is listed as DD when there is very little information available. The data available needs to be so uncertain that everything from LC to CR are plausible categories. This is for example the case when a taxon is only known from the type specimen, which was collected in an unknown place some time ago. DD cannot be used when the available information precludes one of the categories, e.g. when the information indicates that NT to CR would be plausible categories. Similarly, incomplete information is not a reason for DD; here we need to make assumptions based on the information we have.

      Assessment of Cordillera Azul Antbird
      A Red List assessment estimates the extinction risk of a species reflecting the information available at the time of assessment.
      Even though it may sound slightly ironic here, we already know to much about Cordillera Azul Antbird to list it as DD. The uncertainty surrounding the data is relatively high, but we have band estimates of the distribution range, population size and trend. As BirdLife always uses a precautionary approach, we assume that the true values are closer to the lower band of the estimates. We know that the distribution range is too large to qualify for listing as threatened (which excludes categories VU to CR), and that the value we currently have may even need to be revised upwards in case that the species is additionally found in the Cordillera El Sira. We further know that the species may be declining slowly, as forest is lost in unprotected sites within the range. We do not know the exact rate of population decline, but there is no indication that it meets the threshold for VU, which hence excludes the categories VU to CR. If new information becomes available, this will be corrected. Finally, we have a preliminary estimate of the population size, i.e. the conservative estimate of a minimum of 7,000 mature individuals that you provided in your paper. This meets the threshold for VU, and excludes categories EN and CR. From this follows that overall, the species can at maximum be assessed as VU.
      As outlined above, we applied the subcriteria of Criterion C in a very conservative and precautionary way. In your comment, you state that the species likely forms several subpopulations, not just one. Thank you very much for this information; this is very important as it helps to find the correct classification based on the currently available information. Your comment indicates that our application of the subcriteria was indeed too precautionary and requires correction. Consequently, while the population size may (in the worst case) be small enough to meet the threshold for VU under C, the species does not meet enough conditions to qualify for listing as VU. In the absence of information to indicate otherwise, we would still assume that the number of subpopulations is very small, so that the species would approach the threshold for VU under Criterion C2a(ii). Hence, Corillera Azul Antbird may be listed as Near Threatened.

  3. Red List Team (BirdLife International) says:

    Recommended categorisation to be put forward to IUCN
    Following further review, the recommended categorisation for this species has been changed.
    Cordillera Azul Antbird is now recommended to be listed as Near Threatened, approaching the threshold for listing as threatened under Criterion C2a(ii).
    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.

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