This is part of a consultation on the Red List implications of extensive changes to BirdLife’s taxonomy for passerines
Lynx Edicions and BirdLife International will soon publish the second volume of the HBW-BirdLife Illustrated Checklist of the Birds of the World, building off the Handbook of the Birds of the World series, and BirdLife’s annually updated taxonomic checklist.
The new Checklist will be based on the application of criteria for recognising species limits described by Tobias et al. (2010). Full details of the specific scores and the basis of these for each new taxonomic revision will be provided in the Checklist.
Following publication, an open and transparent mechanism will be established to allow people to comment on the taxonomic revisions or suggest new ones, and provide new information of relevance in order to inform regular updates. We are also actively seeking input via a discussion topic here regarding some potential taxonomic revisions that currently lack sufficient information.
The new Checklist will form the taxonomic basis of BirdLife’s assessments of the status of the world’s birds for the IUCN Red List. The taxonomic changes that will appear in volume 2 of the checklist (for passerines) will begin to be incorporated into the 2016 Red List update, with the remainder to be incorporated into subsequent Red List updates.
Preliminary Red List assessments have been carried out for the newly split or lumped taxa. We are now requesting comments and feedback on these preliminary assessments.
Limestone Wren-babbler Gypsophila crispifrons is being moved to genus Turdinus and split into Turdinus crispifrons and T. calcicola, following the application of criteria set out by Tobias et al. (2010).
Prior to this taxonomic change, Limestone Wren-babbler was listed as Least Concern, on the basis that it did not approach the threshold for Vulnerable under any criterion. Turdinus crispifrons (as now defined following the taxonomic change) retains much of the pre-split species’s range and population and is not thought to approach the threshold for Vulnerable under any criterion. Therefore, this species warrants listing as Least Concern.
T. calcicola is found only in the south-western part of north-east Thailand in forest associated with limestone, below 915 m (Collar and Robson 2016). It has a highly restricted range, and it has been stated to only be found in Saraburi Province (Sanguansombat 2005), though there have been several reported sightings outside of this Province (see eBird webpage for the pre-split species, http://ebird.org/). The population size has not been directly estimated but based on an assessment of known records, population densities of closely related species of a similar body size and assuming only a proportion of its range is occupied, the population size likely falls within the range of 2,500-9,999 mature individuals. Low level deforestation is occurring within the range of this species (see Hansen et al. 2013) and so it may be inferred that the species is undergoing a slow continuous decline. Therefore, this species would qualify as Vulnerable under criterion C2a(ii). The species has been listed as Endangered in the regional red list assessment for Thailand (Sanguansombat 2005), and it does have a restricted range; however, the population likely occurs at >>10 locations* and is not severely fragmented and so would not qualify as threatened under criterion B. We request any further information regarding population size and trend estimates to ascertain whether it would warrant listing as Endangered under another criterion, but in the absence of any such information it is proposed that this species be listed as Vulnerable under criterion C2a(ii).
Comments are invited on these proposed categories and further information would be welcomed.
*Note that the term ‘location’ defines a geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals of the taxon present. The size of the location depends on the area covered by the threatening event and may include part of one or many subpopulations. 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).
Collar, N. and Robson, C. 2016. Limestone Wren-babbler (Gypsophila crispifrons). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/59530 on 11 October 2016).
Hansen, M. C., P. V. Potapov, R. Moore, M. Hancher, S. A. Turubanova, A. Tyukavina, D. Thau, S. V. Stehman, S. J. Goetz, T. R. Loveland, A. Kommareddy, A. Egorov, L. Chini, C. O. Justice, and J. R. G. Townshend. 2013. High-Resolution Global Maps of 21st-Century Forest Cover Change. Science 342: 850–53. Data available on-line from: http://earthenginepartners.appspot.com/science-2013-global-forest. Accessed through Global Forest Watch on 10th October 2016. www.globalforestwatch.org
IUCN. 2001. IUCN Red List Categories and Criteria: Version 3.1. Gland, Switzerland and Cambridge, UK: IUCN Species Survival Commission.
IUCN. 2012. Guidelines for Application of IUCN Red List Criteria at Regional and National Levels: Version 4.0. Gland, Switzerland and Cambridge, UK: IUCN.
Sanguansombat, W. 2005. Thailand Red Data : Birds. Office of Natural Resources and Environmental Policy and Planning, Bangkok, Thailand.
Tobias, J. A., Seddon, N., Spottiswoode, C. N., Pilgrim, J. D., Fishpool, L. D. C. and Collar, N. J. 2010. Quantitative criteria for species delimitation. Ibis 152: 724–746.