Archived 2016 topics: Olive Thrush (Turdus olivaceus) is being split: list T. roehli 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.

Olive Thrush Turdus olivaceus is being split into T. olivaceus, T. abyssinicus, T. smithi and T. roehli, following the application of criteria set out by Tobias et al. (2010).

Prior to this taxonomic change, T. olivaceus was listed as Least Concern, on the basis that it did not approach the threshold for Vulnerable under any criterion. T. olivaceus (as now defined following the taxonomic change) has a very large range encompassing southern Malawi, Mozambique, Swaziland, and eastern and southern South Africa; T. smithi is found in southern Namibia, south-eastern Botswana and northern South Africa; and T. abyssinicus is found throughout central to eastern Africa, occurring from Eritrea and Ethiopia south through Uganda, Kenya and eastern Democratic Republic of Congo to northern Malawi and north-eastern Zambia. All three species are not thought to be under significant threat, and are generally common to abundant (Collar 2016). Therefore, they warrant listing as Least Concern.

T. roehli is found in north-east Tanzania in the North Pare and Usambara Mountains (Zimmerman et al. 1996). It preferentially uses primary forest and only slightly disturbed forest (Newmark et al. 2010), which is likely to be declining as a result of encroachment of subsistence agriculture and wood extraction (e.g. Goodman et al. 1995). Negative population growth rates have also been reported for this species in some parts of its range (Newmark, 2006) and so the global population trend is thought to be declining. The population is also likely fragmented as while it may be well reported (found at all sites in Newmark et al. [2010]), it was not found in adjacent forest fragments over 20 years of study (Newmark et al. 2010). Therefore, the species likely at least qualifies as Near Threatened under criterion B1ab(ii,iii,v), and we request any information regarding whether it may be severely fragmented (see IUCN 2001, 2012) as this would probably warrant the species being listed as Vulnerable.

Comments are invited on these proposed categories and further information would be welcomed.

 

References:

Collar, N. 2016. Olive Thrush (Turdus olivaceus). 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/58279 on 30 September 2016).

Goodman, S. M., Stanley, W. T., Newmark, W. D. and Howell, K. M. 1995. The Ambangulu Forest, West Usambara Mountains, Tanzania: a threatened Eastern Arc forest. Oryx 29: 212-214.

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.

Newmark, W.D. 2006. A 16-year study of forest disturbance and understory bird community structure and composition in Tanzania. Conserv. Biol. 20: 122–134.

Newmark, W.D., Mkongewa, V.J. and Sobek, A.D. 2010. Ranging behavior and habitat selection of terrestrial insectivorous birds in north-east Tanzania: implications for corridor design in the Eastern Arc Mountains. Anim. Conserv. 13: 474-482.

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.

Zimmerman, D.A., Turner, D.A and Pearson, D.J. 1996. Birds of Kenya and Northern Tanzania. Christopher Helm, London.

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One Response to Archived 2016 topics: Olive Thrush (Turdus olivaceus) is being split: list T. roehli 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:

    T. olivaceus, T. smithi and T. abyssinicus as Least Concern.

    T. roehli as Near Threatened under criterion B1ab(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.