Archived 2011-2012 topics: Bolivian Recurvebill (Simoxenops striatus) and Ashy Antwren (Myrmotherula grisea): downlist both to Least Concern?

Initial deadline for comments: 31 January 2012 [note that this has been moved back by about two months].

BirdLife species factsheets for Bolivian Recurvebill and Ashy Antwren

Bolivian Recurvebill Simoxenops striatus and Ashy Antwren Myrmotherula grisea occupy very similar known ranges in the Yungas of Bolivia, ranging into extreme south-eastern Puno, Peru. They both inhabit foothill and lower montane forests, although their exact habitat requirements appear to differ somewhat. Both are listed as Near Threatened under criterion B1a+b(i,ii,iii,v) on the basis that they have moderately small ranges, with on-going declines taking place in their Extents of Occurrence (EOOs), Areas of Occupancy (AOOs), area, extent and/or quality of habitat and number of mature individuals. Neither species is regarded as having severely fragmented habitat (over 50% in patches too small to support viable populations), although both species were previously thought to occur at only 6-10 locations.

Information published by Herzog et al. (2008), however, indicates that both species are known from more than 10 locations. Remapping of their ranges with reference to the data presented by Herzog et al. (2008) has resulted in new estimates for their EOOs of over 80,000 km2. This, coupled with their occurrence at more than 10 locations, suspected slow rates of population decline and presence of large areas of intact primary forest within their respective ranges, suggests that they should be downlisted to Least Concern, as they can no longer be considered to approach the thresholds for Vulnerable under any of the IUCN criteria, including B1.

Updated BirdLife range map for Bolivian Recurvebill (click on map to see larger version)

Updated BirdLife range map for Ashy Antwren (click on map to see larger version)

Comments are invited on these proposed category changes and further information on these species is sought to assist with the assessment of their threat status.


Herzog, S. K., Hennessey, A. B., Kessler, M. and García-Solíz, V. H. (2008) Distribution, natural history and conservation status of two endemics of the Bolivian Yungas, Bolivian Recurvebill Simoxenops striatus and Yungas Wren Myrmotherula grisea. Bird Conserv. Int. 18: 331-348.

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5 Responses to Archived 2011-2012 topics: Bolivian Recurvebill (Simoxenops striatus) and Ashy Antwren (Myrmotherula grisea): downlist both to Least Concern?

  1. Ross MacLeod says:

    Down listing of both species is suggested, largely based on new Extent of Occurrence calculations suggesting EOO > than 80,000 km2, with EOO taken as a proxy for range size. However for these species EOO is a poor proxy for range size because, as the maps above indicate, the species have long, narrow ranges and individual records on outlying extensions of the Andes can widen the EOO to include large areas within which the species is never found, these species also have altitudinal ranges which are not reflected in the EOO. Herzog et al. 2008 use more detailed mapping criteria to calculate range sizes of 29,755 k for Ashy Antwren, and 37,130 km for Bolivian Recurvebill and these are more likely to be representative of the species ranges. The picture is further complicated by Bolivian Recurvebill’s strong preference for bamboo, large areas of which are uncommon in parts of the range. Neither species qualifies for threatened but the true range of each species seems likely to be small and probably not much greater than the 20,000 km2 vulnerable threshold. There is no information available on area of occupancy but particularly for Recurvebill it doesn’t seem unrealistic that given its habitat preferences this could be 10% of over all range, which suggest AOOs greater than but approaching the vulnerable threshold of 2000 km2. From personal observation the Bolivian Yungas, which makes up the vast majority of these species ranges, is currently facing ongoing and systematic habitat destruction and degradation along the lower edges that these species inhabit. Clearance for subsistence and commercial agriculture and by logging are ongoing at rates that suggest the Area of Occupancy, the area of habitat and the quality of habitat are all likely to have declined significantly in the last decade and are likely to decline even more in the next decade. Declines of between 10 and 20% due to habitat loss or degradation seem possible over the next 10 years, approaching criteria A2c. The species both seem likely to be approaching vulnerable under B2a+b+c, with severe fragmentation due to habitat destruction B1 likely in the future. In accordance with Herzog et al. I would suggest these species should be classified Near-threatened due to ongoing habitat loss and degradation.

  2. Joe Taylor says:

    The following comments were sent by Sebastian Herzog and were approved for posting on 24 October 2011:

    I took a look at your justification and range maps for suggesting downlisting. For the Yungas Antwren as I prefer to call it, downlisting may be justified given it was recently found in Cusco department. Re. the Recurvebill, as far as I know the LSU specimens from the Putina Puncu-Curva Alegre area in very extreme southeast Peru are the northernmost records, but I may be wrong.

    I see a fundamental problem with your/BirdLife’s range maps, though, on which you base the EOO estimates. They include large areas outside the known elevational range of both species and therefore overestimate EOO.

  3. Concur with the comments above for both Ashy Antwren and Bolivian Recurvebill. Both species should probably be revised to Near-threatened rather than Least Concern, largely on basis of much smaller EOO than calculated and greater risk of future degradation and fragmentation of habitats.

  4. Joe Taylor says:

    A recent analysis of the effects of projected deforestation in Amazonia on bird species population trends (Bird et al. 2011) suggests that S. striatus and M. grisea do not qualify for any category higher than Least Concern under criterion A4, although of course this does not preclude their listing as Near Threatened or higher under other criteria. For further details, please see the topic entitled ‘Input required on proposal to uplist a suite of Amazonian birds owing to predicted declines from projected forest loss’ (

  5. I concur with the downlisting of at least Simoxenops striatus to Least Concern. On a recent trip to the La Paz yungas near the village of Illampu, I easily found this species at c. 1500m in very degraded bamboo regrowth. There was no primary or even decent secondary habitat anywhere within sight distance. The whole valley was covered with dense 2-m regrowth dominated by bamboo, and the species was easy to come by using sound (and sight) as an indicator. Simoxenops striatus seems to have a great tolerance to habitat degradation. Indeed it may be a gap species that is benefitting from human-induced habitat alteration.

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