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.
Short-tailed Batis Batis mixta is being split into B. mixta and B. reichenowi, following the application of criteria set out by Tobias et al. (2010).
Prior to this taxonomic change, B. mixta was listed as Least Concern on the basis that it did not approach the threshold for Vulnerable under any criteria. B. mixta (as defined following the taxonomic change) is found in forest and wooded habitat in north-east Tanzania and coastal south-east Kenya (Louette 2016a). There has been some habitat destruction in this range (see BirdLife International 2013), but the species remains common, inhabiting nearly all evergreen forest patches within its range (Louette 2016a). Therefore, the species is not thought to approach the threshold for Vulnerable under any category, and so it is proposed that it be listed as Least Concern.
B. reichenowi is known from a small area of coastal lowland forest in south-east Tanzania (Louette 2016b), and it is possible that it may also occur in a separate area near the Rufiji River (Louette 2016b). Based on current knowledge, however, it is restricted to an Extent of Occurrence of 12,350 km2. Its population is inferred to be declining because the coastal lowland forest of Tanzania is threatened by habitat clearance for agriculture (Kashiagili et al. 2013), and although there has been a slowing in the rate of forest clearance, the loss of this habitat continues (Kashiagili et al. 2013). There is, however, a lack of information regarding the potential population size of this species. Given its restricted range, the population size is not predicted to be very large, but it is uncertain whether there may be fewer than 10,000 mature individuals, nor whether it is restricted to a single subpopulation or several small subpopulations of <1,000 mature individuals, determining whether the species meets the thresholds for listing as Vulnerable under criterion C2. Therefore, we request any further information about the likely population size of this species, and whether there have been any confirmed records from the area near the Rufiji River to see whether it warrants listing as Vulnerable under criterion C2a(i) or C2a(ii). Alternatively, if it approaches the thresholds for listing as Vulnerable it may be listed as Near Threatened, otherwise it will likely be classified as Least Concern.
BirdLife International. 2013. Biodiversity status and trends report for the Eastern Arc Mountains and coastal forests of Kenya and Tanzania Region, 2012. Nairobi: BirdLife International – Africa Partnership Secretariat.
Kashiagili, J., Mbilinyi, B., Tabor, K., Hall, J., Malugu, I., Sumbi, P., Kijazi, A. and Burgess, N. D. 2013. Tanzania is losing its biodiversity-rich coastal forests: Deforestation in Tanzania’s coast forests. The Arc Journal 28: 5-7
Louette, M. 2016a. Short-tailed Batis (Batis mixta). 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/59115 on 14 September 2016).
Louette, M. 2016b. Reichenow’s Batis (Batis reichenowi). 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/59114 on 14 September 2016).
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.