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.
Black-chinned Laughingthrush Strophocincla cachinnans is being moved to genus Trochalopteron and split into T. cachinnans and T. jerdoni, following the application of criteria set out by Tobias et al. (2010).
Prior to this taxonomic change, Black-chinned Laughingthrush was listed as Endangered under criterion B1ab(i,ii,iii,iv,v), on the basis that it had a ‘very small and severely fragmented range which is declining rapidly as a result of the conversion of forest habitats to plantations, agriculture and settlements’ (BirdLife International 2016). Trochalopteron cachinnans (as now defined following the taxonomic change) is found in forest habitat between 1,200 and 2,300 m with dense undergrowth mainly in the Nilgiris, with a small subpopulation in the Muthikulam hills India (Collar and Robson 2016, Praveen J. and Nameer 2012). T. jerdoni is found in similar habitat to T. cachinnans but is restricted to the hills of Wayanad and Coorg (Praveen J. and Nameer 2012).
The pre-split species’s population was estimated to have a population size of 2,500-9,999 mature individuals based on known records, range size and descriptions of abundance, and this was consistent with population density estimates for congeners and assuming only a proportion of its range was occupied (BirdLife International 2016). Based on the same assumptions the population size of the newly defined T. cachinnans likely remains within the range of 2,500-9,999 mature individuals. The population size of T. jerdoni, however, may fit in the 250-2,500 mature individuals range, although likely with >250 mature individuals in the largest sub-population. We welcome further information regarding this though, as T. jerdoni has been described as locally ‘fairly common’ (Collar and Robson 2016).
The habitat of both species has undergone severe deforestation and conversion to agriculture and infrastructure in the past (BirdLife International 2016), but the rate of deforestation in recent years has declined considerably (see Hansen et al. 2013). Nevertheless there is some habitat clearance occurring and so at least the quality of habitat is declining for these species. The degree to which this may be affecting population trends, however, is not certain; but they may be conservatively said to be in a slow decline, and historical habitat loss has led to both species becoming severely fragmented (see IUCN 2001, 2012). Both species are range restricted, with both probably having an Extent of Occurrence <5,000km2, and T. jerdoni possibly having an Extent of Occurrence of <100km2 (see Praveen J. and Nameer 2012), pending Minimum Convex Polygon analyses. Therefore, T. cachinnans likely warrants listing as Endangered under criterion B1ab(ii,iii,v). T. jerdoni may warrant listing as Critically Endangered under criterion B1ab(ii,iii,v) pending Minimum Convex Polygon analyses, but should meet the threshold for listing as Endangered under criterion B1ab(ii,iii,v).
Comments are invited on these proposed categories and further information would be welcomed.
Collar, N. and Robson, C. 2016. Black-chinned Laughingthrush (Strophocincla cachinnans). 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 fromhttp://www.hbw.com/node/59618 on 12 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.
Praveen J. and Nameer, P.O. 2012. Strophocincla Laughingthrushes of South India: a case for allopatric speciation and impact on their conservation. J. Bombay Nat. Hist. Soc. 109: 46-52.
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.