Archived 2016 topics: Tiny Greenbul (Phyllastrephus debilis) is being split: list P. debilis as Least Concern and P. albigula as Near Threatened or Vulnerable?

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.

Tiny Greenbul Phyllastrephus debilis is being split into P. debilis and P. albigula, following the application of criteria set out by Tobias et al. (2010).

Prior to this taxonomic change, P. debilis was listed as Least Concern on the basis that it did not approach the threshold for Vulnerable under any criterion. P. debilis (as now defined following the taxonomic change) is found in coastal forested areas from central to southern Kenya and north-east Tanzania, as well as in south-east Tanzania, southern Mozambique and inland to the extreme east of Zimbabwe (Fishpool and Tobias 2016). There have been reported declines in the extreme north and south of its range (del Hoyo et al. 2005) but any global decline is not thought to be sufficient to warrant listing as Vulnerable. In addition to this, the species has been described as generally common (Fishpool and Tobias 2016), and so is unlikely to meet the population threshold for Vulnerable (<10,000 individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). Therefore, it is proposed that the species be listed as Least Concern.

P. albigula is found in forest above 300m in the Usambara, Nguru and Nguu Mountains in north-east Tanzania, within an Extent of Occurrence of c.16,600 km2. The pre-split species was described as generally common (Fishpool and Tobias 2016), but within the newly split species’s range clearance and degradation of its forest habitat is occurring and so the population is suspected to be in decline. The species may qualify as Vulnerable under criterion B1ab(i,ii,iii,v) depending on further information about the potential number of locations* where this species may be found. In the absence of this information it is proposed that the species be listed as Near Threatened under criterion B1ab(i,ii,iii,v).

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).


del Hoyo, J., Elliott, A. and Christie, D. 2005. Handbook of the Birds of the World, vol. 10: Cuckoo-shrikes to Thrushes. Lynx Edicions, Barcelona, Spain.

Fishpool, L. and Tobias, J. 2016. Tiny Greenbul (Phyllastrephus debilis). 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 on 16 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.

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.

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1 Response to Archived 2016 topics: Tiny Greenbul (Phyllastrephus debilis) is being split: list P. debilis as Least Concern and P. albigula as Near Threatened or Vulnerable?

  1. James Westrip (BirdLife) says:

    Based on available information, our preliminary proposal for the 2016 Red List would be to list:

    P. debilis as Least Concern.

    P. albigula as Near Threatened under criterion B1ab(i,ii,iii,v).

    There is now a period for further comments until the final deadline of 28 October, after which the recommended categorisations will be put forward to IUCN.

    Please note that we will then only post final recommended categorisations on forum discussions where these differ from the initial proposal.

    The final 2016 Red List categories will be published on the BirdLife and IUCN websites in early December, following further checking of information relevant to the assessments by both BirdLife and IUCN.

Comments are closed.