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.
American Robin Turdus migratorius is being split into T. migratorius and T. confinis, following the application of criteria set out by Tobias et al. (2010).
Prior to this taxonomic change, T. migratorius was listed as Least Concern, on the basis that it did not approach the threshold for Vulnerable under any criterion. T. migratorius (as now defined following the taxonomic change) retains its very large range and population over much of North America and so is not thought to approach the threshold for Vulnerable under any criterion. Therefore it warrants listing as Least Concern.
T. confinis is found only at the southern tip of Baja California Sur, Mexico in arid forest between 1,000 and 2,000m (Howell and Webb 1995). There are no known significant threats or declines in the species and so the population is suspected to be stable. Given its highly restricted range, however, the population could easily become threatened over a very short period of time. The species appears to have persisted despite the occurrence of tropical storms and hurricanes affecting most, if not all, of its range, and so these may not be seen as a major threat. The pre-split species was thought to be highly affected by pesticide use, with the species showing reduced breeding success in orchards treated with DDT, and thousands of individuals dying after the application of Azodrin to a field in Florida in 1972 (see Collar 2016). Therefore, the use of any such chemical within the newly defined species’s range could have a great effect. That said, the likelihood of this occurring may be particularly low, and so the number of locations* where the species is found may in fact not approach the threshold for Vulnerable. We request any further information regarding this species to see whether it may warrant listing as Near Threatened or Vulnerable under criterion D2, but in the absence of any information this species may be listed as Least Concern despite its restricted range.
*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).
Collar, N. (2016). American Robin (Turdus migratorius). 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/58287 on 30 September 2016).
Howell, S. N. G. and Webb, S. 1995. The Birds of Mexico and Northern Central America. Oxford University Press, Oxford.
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.