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.
Yellowish Bulbul Ixos everetti is being moved to genus Hypsipetes and split into Hypsipetes everetti, H. catarmanensis and H. haynaldi, following the application of criteria set out by Tobias et al. (2010).
Prior to this taxonomic change, Yellowish Bulbul was listed as Least Concern, on the basis that it did not approach the threshold for Vulnerable under any criterion. H. everetti (as now defined following the taxonomic change) is not thought to approach the threshold for Vulnerable under any criterion and hence it is proposed that this species be listed as Least Concern.
H. haynaldi is found on the islands of Bongao, Jolo, Sanga Sanga and Tawi-Tawi in south-western Philippines. It is found in lowland forest, forest edge and secondary growth, and the pre-split species was said to prefer intact forest, although it can occur in very small forest patches (Fishpool and Tobias 2016). Habitat loss may be leading to population declines, but these are not thought to be great enough to warrant listing as threatened under criterion A. The population size has not been directly estimated, but using population density measures of congeners and closely related similar species, and assuming only a proportion of its range is inhabited, the population size is unlikely to meet the threshold for Vulnerable (a declining population size of <10,000 all in one subpopulation or ≤1,000 mature individuals per sub-population). The species does still have a restricted range, but the number of locations* where this species is found is unlikely to approach ≤10. Therefore, this species is unlikely to approach the threshold for Vulnerable under any criteria, and so it would warrant listing as Least Concern.
H. catarmanensis is only found in lowland forest and secondary growth on the island of Camiguin, Philippines (Fishpool and Tobias 2016), with an Extent of Occurrence of c.266.5km2. The pre-split species was described as common (Fishpool and Tobias 2016), and this taxon was one of the most commonly caught birds in mist nets in Kital-is, Sagay (Balete et al. 2006). The population size has not been directly estimated but using population density measures of congeners and closely related similar species, and assuming only a proportion of its range is inhabited, the population size is unlikely to meet the threshold for Vulnerable when there is no decline (<1,000 mature individuals). However, the population size may fall in the range of 2,500-9,999 mature individuals, which would qualify the species as Vulnerable under criterion C2a(ii) if a continuing decline was observed, projected or inferred.
There has only been very limited deforestation on Camiguin within the last 3 generations of this species (10.5 years) (data from Hansen et al. 2013), and this may not be sufficient to infer a population decline and would mean that the species is found at >>10 locations* (thus meaning it would not qualify for Vulnerable under criterion B). Therefore, we request any further information regarding current population trends in this species, and the potential for future deforestation on Camiguin, but in the absence of any further information the population will be assumed to be stable, and hence likely warrant listing as Least Concern.
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).
Balete, D.S., Tabaranza Jr., B. R. and Heaney, L. R. 2006. An annotated checklist of the birds of Camiguin Island, Philippines. Fieldiana: Zoology N.S. 106: 58-72.
Fishpool, L. and Tobias, J. 2016. Yellowish Bulbul (Ixos everetti). 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/58032 on 10 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.
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.