Indian Grass-babbler (Graminicola bengalensis): revise global status?

Indian Grass-babbler (Graminicola bengalensis) is found in wet grasslands and swamp habitats of Nepal and northern India. It also occurs in Bangladesh, but it appears to have mostly disappeared from its former range in this country (Collar and Robson 2007). Its stronghold is Nepal, which has been thought to hold c. 2,000 pairs (Leader et al. 2010), and the recent National Red List of Nepal stated that the population size there may be in the range 2,000-5,300 (Inskipp et al. 2016), though it is not stated whether this refers to all individuals or just mature individuals, as would be expected from the IUCN definition of ‘population size’ (see IUCN Standards and Petitions Subcommittee 2017). Therefore, the overall population size is likely best placed in the range 2,500-9,999 mature individuals.

Being restricted to undisturbed grasslands, the species is under threat from habitat loss, modification and overgrazing. As such the species is currently considered to be undergoing a continuing decline.

The National Red List of Nepal assessed the species to be Endangered (Inskipp et al. 2016), but this cannot be directly replicated at the global scale as the key threshold that was looked at was Area of Occupancy (AOO), and obviously the total AOO is going to be larger than that within just one range state. However, the species is currently listed as Least Concern globally (BirdLife International 2017) and considering how the species’ stronghold is Nepal, Indian Grass-babbler may warrant a reassessment at the global scale. Therefore, we have assessed the global status of the species under all criteria.

 

Criterion A – While we may be fairly confident that threats are causing this species to decline, there has been no quantification of the rate of decline, and so the species cannot be accurately assessed against this criterion.

 

Criterion B – The species has an Extent of Occurrence (EOO) of 467,000km2 so it does not meet the threshold for listing as Vulnerable under criterion B1. The species is listed as Endangered under criterion B2 in Nepal (Inskipp et al. 2016). However, this assessment does not state what Area of Occupancy (AOO) value was used, or how it was calculated. The global AOO has not been calculated, but given the global EOO, the likely global AOO likely exceeds the threshold for Vulnerable under this criterion (2,000km2). Therefore, the species likely does not warrant listing as globally threatened under this criterion.

 

Criterion C – The species’ population size is considered to fall in the range 2,500-9,999 mature individuals, which meets the threshold for Vulnerable under criterion C, and it may be inferred to be undergoing a continuing decline as a result of habitat loss; but to be listed as Vulnerable requires other conditions to be met.

The rate of decline is not certain and the species is not known to undergo extreme fluctuations so it does not warrant listing under criteria C1 and C2b respectively. The species is considered to be fragmented in Nepal (Inskipp et al. 2016), and this is likely the case throughout its range. Therefore, it is unlikely to warrant listing under criterion C2a(ii).

It could still warrant listing as Vulnerable under criterion C2a(i), but this would require there to be ≤1,000 mature individuals per subpopulation. Without clear subpopulation estimates it is difficult to assess whether this may be the case or not. In the absence of further information, though, if the lower population estimate of Inskipp et al. (2016) is used then it may be possible that the largest subpopulation is ≤1,000 mature individuals. However, given the large amount of uncertainty over this it may be more appropriate to list the species as Near Threatened under criterion C2a(i) unless further information is available.

 

Criterion D – The population size and range are too large to warrant listing this species as Vulnerable 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.

 

Therefore, in the absence of any further information Indian Grass-babbler may warrant listing as Near Threatened under criterion C2a(i); although if further information is available to suggest that no subpopulation contains >1,000 mature individuals then the species may warrant listing as Vulnerable under the same criterion.

 

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 information that is sought, or about the species’ Red List status.

 

References

BirdLife International. 2017. Species factsheet: Graminicola bengalensis. Downloaded from http://www.birdlife.org on 06/12/2017.

Collar, N. J.; Robson, C. 2007. Family Timaliidae (babblers). Pp.70– 291 in J. del Hoyo, A. Elliott & D. A. Christie (eds.). Handbook of the birds of the world, volume 12. Lynx Edicions, Barcelona.

Inskipp, C.; Baral, H. S.; Phuyal, S.; Bhatt, T. R.; Khatiwada, M.; Inskipp, T.; Khatiwada, A.; Gurung, S.; Singh, P. B.; Murray, L.; Poudyal, L.; Amin, R. 2016. The Status of Nepal’s birds: the National Red List Series. Zoological Society of London, U.K.

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. Downloadable from http://www.iucnredlist.org/documents/RedListGuidelines.pdf.

Leader, P. J.; Carey, G. J.; Olsson, U.; Baral, H. S.; Alström, P. 2010. The taxonomic status of Rufous-rumped Grassbird Graminicola bengalensis, with comments on its distribution and status. Forktail 26: 121-126.

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