Naga Wren-babbler (Spelaeornis chocolatinus): revise global status?

BirdLife species factsheet for Naga Wren-babbler

Naga Wren-babbler (Spelaeornis chocolatinus) occurs the states of Nagaland and Manipur in north-eastern India. It is endemic to a restricted range, where it is scarce, but locally common. The population is preliminarily estimated to number 2,500-9,999 mature individuals. The species inhabits montane evergreen forests at 1,200-3,100 m. It requires a densely vegetated, bushy undergrowth, but is also often found at forest edges and in clearings. The species is suspected to be undergoing a slow decline because of logging and forest clearance for small-scale agriculture.

Naga Wren-babbler is currently listed as Near Threatened, approaching the threshold for listing as threatened under Criterion C2a(ii) (BirdLife International 2019). However, using new information regarding population trends and structure, this species appears to warrant a change in Red List status. Therefore, we present here our reassessment against all criteria for the species.

Criterion A – The population trend for this species has not been directly estimated. However, deforestation data from between 2000 and 2012 (Tracewski et al. 2016) suggest that the area of forested habitat within the species’s range is on average declining by c. 3% over three generations (13.2 years). Even though Naga Wren-babbler might tolerate some forest fragmentation, we can tentatively assume that the rate of population decline is equivalent to the rate of forest loss. Therefore, while it may be possible to consider the species to be in decline, the rate of decline is likely to be slow and would not approach the threshold for Vulnerable under this criterion. Therefore, Naga Wren-babbler may be listed as Least Concern under Criterion A.

Criterion B – The Extent of Occurrence (EOO) for this species is 11,200 km2. Therefore, the EOO meets the threshold for Vulnerable under Criterion B1 (EOO < 20,000 km2). The Area of Occupancy (AOO) for the species has not been quantified; thus it cannot be assessed against Criterion B2. However, to be listed under Criterion B1, at least two of three further conditions have to be met.

Naga Wren-babbler is assumed to occur at more than 10 locations* (BirdLife International 2019). However, it is possible that the species approaches this threshold. The species is not severely fragmented per IUCN definition (see IUCN Standards and Petitions Subcommittee 2017), as all individuals most likely belong to the same subpopulation. Naga Wren-babbler therefore does not meet condition (a) (severely fragmented or ≤ 10 locations), but likely approaches it. AOO, area, extent and/or quality of habitat as well as the number of mature individuals are declining, and hence the species meets condition (b) under subconditions (ii,iii,v). However, Naga Wren-babbler does not undergo extreme fluctuations and so does not meet condition (c).

Therefore, even though Naga Wren-babbler occurs in a small range and has a restricted EOO, it does not trigger sufficient conditions for listing as Vulnerable under criterion B, but it meets one further condition and approaches the second.  As such, it may be listed as Near Threatened under Criterion B1ab(ii,iii,v).

Criterion C – The population of Naga Wren-babbler is estimated to number 2,500-9,999 mature individuals. This meets the threshold for listing as Vulnerable (< 10,000 mature individuals). Yet, in order to be listed under Criterion C, other conditions have to be fulfilled.

The population decline has been inferred from the rate of forest loss within its range (see Tracewski et al. 2016). Therefore, the species cannot be fully trigger a listing as Vulnerable Criterion C1, as this would require a higher level of confidence about the rate of population decline. However, the suspected rate of decline from Tracewski et al. (2016) is still too low to approach the threshold for Vulnerable under C1, so it would not warrant listing as Near Threatened.

The species can, though, be more clearly assessed against Criterion C2. In order to be listed under C2, Naga Wren-babbler needs to have a certain subpopulation structure. We assume that all individuals belong to the same subpopulation; thus the species meets the condition a(ii). The population is not known to undergo extreme fluctuations, and so does not meet condition (b). Overall, due to its having a small, declining population with all mature individuals in the same subpopulation, Naga Wren-babbler may be listed as Vulnerable under Criterion C2a(ii).

Criterion D – The species’s population size and range are too large to warrant listing as threatened, and thus Naga Wren-babbler may be considered Least Concern under Criterion D.

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

Therefore, it is suggested that Naga Wren-babbler (Spelaeornis chocolatinus) be listed as Vulnerable under Criterion C2a(ii). We welcome any comments on the proposed listing and specifically ask for up-to-date information on population size and subpopulation structure.

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’ Red List status. Therefore, please make sure your comments are relevant to the species’ Red List status and the information requested.

*The term ‘location’ refers to a distinct area in which a single threatening event can rapidly affect all individuals of the taxon present, with the size of the location depending on the area covered by the threatening event. 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).

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.

References

BirdLife International. 2018. Species factsheet: Spelaeornis chocolatinus. www.birdlife.org (Accessed 10 April 2019).

IUCN. 2001. IUCN Red List Categories and Criteria: Version 3.1. IUCN Species Survival Commission. IUCN, Gland, Switzerland and Cambridge, U.K.

IUCN. 2012. IUCN Red List Categories and Criteria: Version 3.1. Second edition. IUCN Species Survival Commission. IUCN, Gland, Switzerland and Cambridge, U.K. www.iucnredlist.org/technical-documents/categories-and-criteria.

IUCN Standards and Petitions Subcommittee. 2017. Guidelines for Using the IUCN Red List Categories and Criteria. Version 13. Prepared by the Standards and Petitions Subcommittee. http://www.iucnredlist.org/documents/RedListGuidelines.pdf.

Tracewski, Ł.; Butchart, S. H. M.; Di Marco, M.; Ficetola, G. F.; Rondinini, C.; Symes, A.; Wheatley, H.; Beresford, A. E.; Buchanan, G. M. 2016. Toward quantification of the impact of 21st-century deforestation on the extinction risk of terrestrial vertebrates. Conservation Biology 30: 1070-1079.

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4 Responses to Naga Wren-babbler (Spelaeornis chocolatinus): revise global status?

  1. R.K. Birjit Singh, Manipur India says:

    The population of the species has been declining fast due to habitat loss, massive logging and forest clearance for jhum cultivation at the montane forest areas of Ukhrul and Senapati District of Manipur bordering Nagaland and Myanmar. Although there is no systematic and dedicated studies for the species but it become too hard to sight the species now a days.Therefore, it is suggested that Naga Wren-babbler (Spelaeornis chocolatinus) be listed as Vulnerable under Criterion C2a(ii).

  2. Rob Martin (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.

  3. Praveen J says:

    Historically, all birds used to belong to one single population – however, the way deforestation and jhoom cultivation (slash & burn) has affected its population structure & genetic diversity is anybody’s guess. The bird is still local to the ravines of primary forests (e.g. Khonoma Nature Conservation & Tragon Sanctuary, Sukhai Community Conservation Area) and avoids the secondary jungles.
    Though eBird is not a reflection of the true status of a species like this, as traveling birders target only best areas, most recent records have been from two areas, indicating contraction in its range and associated declines.

    https://ebird.org/india/map/ltwbab1?neg=true&env.minX=44.78346136474613&env.minY=3.7125256240583844&env.maxX=120.80953863525394&env.maxY=39.62448967848706&zh=true&gp=false&ev=Z&mr=1-12&bmo=1&emo=12&yr=all&byr=1900&eyr=2019
    (An indication of same size: ~1000 checklists from Nagaland https://ebird.org/india/region/IN-NL?yr=all)

    Proposal to list this as Vulnerable under C2a(ii) seems apt.

  4. Praveen J says:

    I used eBird records to calculate EOO & AOO.

    EOO: 359 sq.km (MCP) – much lower than EOO mentioned in the summary. Status in the adjacent hills in Manipur is unknown though it has been collected in 1950s from that state (Karong). However, 11,200 EOO seems to be an over-estimate in my opinion.

    AOO: 336 sq.km (if I use polygons of size 1/16th of a degree) – but, this would be less accurate due to sparse sampling. We need more surveys to arrive at a realistic AOO.

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