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.
The newly described taxon Cambodian Tailorbird Orthotomus chaktomuk is to be recognised as a species by BirdLife following the application of the Tobias et al. (2010) cirteria, which support its distinctiveness from congeners.
Cambodian Tailorbird O. chaktomuk is found within the extent of the seasonally flooded dense scrub within the floodplain of the Tonle Sap, Mekong and Bassac Rivers in Cambodia, however it is restricted to the vicinity of meeting location of these waterbodies (Mahood et al. 2013). It occupies dense humid evergreen scrub 2-6m tall in areas that experience flooding on an annual basis (Mahood et al. 2013). The extent of occurrence (EOO, calculated from a Minimum Convex Polygon of known distributional records) of the species is 11,700km2. It is considered to likely rely on human disturbance of the floodplain habitat that prevents tall floodplain forest from establishing in this region continually inhabited by people for an exceedingly long time (Mahood et al. 2013).
Within suitable habitat it is often the commonest bird, and the population, although not quantified, is not thought to approach the thresholds for listing under criterion C.
An assessment based on satellite imagery and ground vegetation plots within the range of the species has indicated a recent, and ongoing rapid decline in extent of habitat suitable for the species that approaches 30% (R. Carvill unpub. data), and subsequently extreme El Nino related fires have impacted the remaining area severely in 2016 (S. Mahood in litt. 2016). The species has already been noted to have disappeared from one site following conversion to aquaculture ponds (Mahood et al. 2013). Despite this, it is considered that the species still occurs at considerably in excess of 10 locations* when the threat is considered to be habitat loss. While the species is anticipated to be able to recover from events such as fires, and additional areas of scrub are likely to appear in new sites to replace some that is lost, the ongoing conversion of habitat is inferred to have caused a population reduction that may approach the thresholds for Vulnerable under the population size reduction criterion over the past, current and future 10-year periods.
As such it is proposed that Cambodian Tailorbird O. chaktomuk be listed as Near Threatened as it is inferred it is suffering a population decline that approaches the thresholds for listing as Vulnerable under criterion A2c+A3c+A4c. 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).
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.
Mahood, S.P., John, A.J.I., Eames, J.C., Oliveros, C.H., Moyle, R.G., Hong Chamnan, Poole. C. M., Nielsen, H. and Sheldon, F.H. 2013. A new species of lowland tailorbird (Passeriformes: Cisticolidae: Orthotomus) from the Mekong floodplain of Cambodia. Forktail 29: 1-14.
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.