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.
Olive-flanked Whistler Hylocitrea bonensis is being split into H. bonensis and H. bonthaina, following the application of criteria set out by Tobias et al. (2010).
Prior to this taxonomic change, H. bonensis (BirdLife species factsheet) was listed as Least Concern, as although the species may have had a restricted range, it was still not believed to approach the thresholds for Vulnerable under any criteria. The pre-split species was characterised as uncommon from 1,200 m upwards and moderately common to common between 2,000 and 3,500 m in montane forest, especially moss forest (Boles 2016).
H. bonensis (as defined following the taxonomic changes) is found at higher elevations throughout the mountains of N, C and SE Sulawesi, while H. bonthaina is restricted to the slopes of Gunung Lompobattang in south west Sulawesi. The Extent of Occurrence of the latter is under 1,000km2, and the removal of this from the range of H. bonensis is not thought to change the assessment for that species, hence it is suggested that H. bonensis is considered Least Concern.
H. bonthaina is presumed to share a similar range to the Endangered Lompobatang Flycatcher Ficedula bonthaina. There seem very few modern observations, though one was observed in July 2016 (M. Nelson in litt. 2016). This is despite a considerable increase in the number of observers seeing F. bonthaina in locations that should be suitable for both species. On a precautionary basis it is therefore considered to occur at five or fewer locations*.
The population is estimated to number 2,500-9,999 mature individuals based on an assessment of known records, descriptions of abundance and range size. This is consistent with recorded population density estimates for congeners or close relatives with a similar body size, and the fact that only a proportion of the estimated Extent of Occurrence is likely to be occupied. There is thought to be a single subpopulation.
Montane forest is becoming highly fragmented around Gunung Lompobattang due to selective logging and clearance for plantations, livestock grazing and encroachment by settlement and cultivation. Forest has been almost totally cleared below 1,000 – 1,500 m (BirdLife International 2001). The species is therefore likely to be suffering an ongoing decline in its area of occupancy, the area, extent and/or quality of habitat and in the number of mature individuals.
H. bonthaina is suggested to be listed as Endangered under criterion B1ab(ii,iii,v).
In addition, the species qualifies as Vulnerable under criterion C2a(ii).
If there is evidence that there has been a population decline in excess of 50% over the previous, current or future three generational period (20.1 years), then it would also qualify as Endangered 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).
Boles, W. (2016). Yellow-flanked Whistler (Hylocitrea bonensis). 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/59333 on 30 September 2016).
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.
BirdLife International. 2001. Threatened birds of Asia: the BirdLife International Red Data Book. BirdLife International, Cambridge, U.K.
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.