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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