Archived 2014 discussion: Fraser’s Eagle-owl (Bubo poensis) and Usambara Eagle-owl (B. vosseleri) are being lumped as B. poensis: list the newly defined species as Least Concern?

The initial deadline for comments on this topic is 10 March 2014, and is therefore later than for most other topics currently under discussion.

This is part of a consultation on the Red List implications of extensive changes to BirdLife’s taxonomy for non-passerines

Lynx Edicions and BirdLife International will soon publish 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 1 of the checklist (for non-passerines) will begin to be incorporated into the 2014 Red List update, with the remainder, and those for passerines (which will appear in volume 2 of the checklist), 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.

Fraser’s Eagle-owl Bubo poensis and Usambara Eagle-owl B. vosseleri are being lumped as B. poensis, following the application of criteria set out by Tobias et al. (2010).

Prior to the taxonomic change, B. poensis (BirdLife species factsheet), a widespread resident of primary evergreen forest, secondary forest, clearings and cardamom plantations in West and Central Africa, mostly in the lowlands, but up to 1,600 m in Cameroon (König and Weick 2008), was listed as being of Least Concern, on the basis that it was not thought to approach the thresholds for Vulnerable under any of the IUCN Red List criteria.

B. vosseleri (BirdLife species factsheet), a resident of mainly montane and submontane evergreen forest in Tanzania, was listed as Vulnerable under criterion B1ab(ii,iii,v), on the basis of its small range (c.19,600 km2), in which remaining areas of suitable habitat are severely fragmented and being cleared and degraded.

Following the taxonomic change, it is suggested that B. poensis be listed as being of Least Concern, on the basis that it is not thought to approach the thresholds for Vulnerable under any of the IUCN Red List criteria.

However, it is noted that whilst poensis was thought to have a stable population prior to the taxonomic change, this could be an erroneous assumption given its distribution in West Africa where deforestation rates are known to have been rapid. For example, Allport (1991) estimated that c.77% of forest cover in the Upper Guinea Endemic Bird Area (EBA) (BirdLife EBA factsheet) had been lost at the time of that study, mainly as a result of logging, agricultural encroachment and mining, and forest loss in the region has continued since that date at a high rate (H. Rainey in litt. 2010). Indeed, this taxon was has been described as threatened by forest destruction and probably persecution, at least locally (König and Weick 2008). Despite this, its apparent tolerance of some forms of habitat modification may buffer the overall impacts to some extent. Information is requested on the likely population trend of the newly-defined species. The species could qualify as Near Threatened under criterion A if it is estimated, projected or suspected to experience a population decline approaching 30% over 35 years (estimate of three generations).

Comments are invited and further information would be welcomed.


Allport, G. (1991) The status and conservation of threatened birds in the Upper Guinea Forest. Bird Conservation International 1: 53–74.

König, C. and Weick, F. (2008) Owls of the World. Second Edition. London, UK: Christopher Helm.

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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6 Responses to Archived 2014 discussion: Fraser’s Eagle-owl (Bubo poensis) and Usambara Eagle-owl (B. vosseleri) are being lumped as B. poensis: list the newly defined species as Least Concern?

  1. Maybe I missed this, but is there a summary somewhere with guidelines or a breakdown of the newly established criteria for species limits (per Tobias et al. 2010)? This would help people with little access to this information to comment in more depth. As is, I am unaware of any DNA studies that supports the splitting of these two widely distributed populations. In recent studies in western Africa, I have seen data where species considered as “widespread” and listed as least concern have 5-10% differences between or among adjacent populations. I’d therefore like to understand how the lumping of these two populations was determined.

    • Joe Taylor says:

      Dear Nobby,

      Thank you for your comments and questions.

      The Tobias et al. (2010) paper can be downloaded via a link at the top of the forum topic.

      Regarding this taxonomic change, although vosseleri has been treated as a separate species because of its geographical isolation and presumed vocal differences, as well as size and plumage differences, evidence suggests that vocal differences are only slight (Hunter et al. 1998, Dowsett-Lemaire 2006).


      Dowsett-Lemaire, F. (2006) Ecology, voice and territorial competition of two forest eagle owls, Fraser’s Eagle Owl Bubo poensis and Akun Eagle Owl B. leucostictus. Bull. African Bird Club 13: 147–156.

      Hunter, N., Carter, C. and Mlungu, E. (1998) A new location for the Usambara Eagle Owl Bubo vosseleri. Scopus 20: 52–53.

  2. Hugo Rainey says:

    Although the rate of loss of B. poensis habitat in West Africa is high, the majority of its range in Central Africa is not declining at anywhere near such a rate. Therefore it seems unlikely that this species should be listed as near-threatened.

  3. Andy Symes says:

    Preliminary proposals

    Based on available information and comments posted above, our preliminary proposal for the 2014 Red List would be to treat the newly-defined Fraser’s Eagle-owl Bubo poensis as Least Concern.

    There is now a period for further comments until the final deadline of 31 March, after which recommended categorisations will be put forward to IUCN.

    The final Red List categories will be published on the BirdLife and IUCN websites in mid-2014, following further checking of information relevant to the assessments by both BirdLife and IUCN.

  4. Duncan Wilson says:

    Having just watched a Fraser’s Eagle-owl foraging in the middle of a large village (Nyososo) in Cameroon, several hundred metres from farmbush and even further from undisturbed primary forest, I would suggest that its tolerance for habitat modification must be quite significant.

  5. Andy Symes says:

    Recommended categorisation to be put forward to IUCN

    Following further review, there has been no change to our preliminary proposals for the 2014 Red List status of this species.

    The final categorisation will be published later in 2014, following further checking of information relevant to the assessment by BirdLife and IUCN.

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