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.
Spotted Towhee Pipilo maculatus is being split into P. maculatus and P. socorroensis, following the application of criteria set out by Tobias et al. (2010).
Prior to this taxonomic change, P. maculatus was listed as Least Concern, on the basis that it did not approach the threshold for Vulnerable under any criterion. P. maculatus (as now defined following the taxonomic change) retains much of the pre-split species’s range and population and is not thought to approach the threshold for Vulnerable under any criterion, and so would warrant listing as Least Concern.
P. socorroensis is found only on the Island of Socorro, Mexico, and it appears to favour a relatively undisturbed habitat dominated by shrubs and ferns (Rodriguez-Estrella et al. 1996). The proliferation of sheep on the island therefore impacted this species as its favoured vegetation was destroyed (Rodriguez-Estrella et al. 1996). Population density estimates range from 20 to 680 individuals per km2 depending on the quality of habitat (Rodriguez-Estrella et al. 1996), thus a population size in the range of 2,500-9,999 mature individuals is probably the most appropriate. While the feral sheep have now been removed from Socorro (Ortiz-Alcaraz et al. 2016) any carrying-over, long-term impact that sheep had on the island is uncertain, and the removal of sheep from the island has been very recent (Ortiz-Alcaraz et al. 2016). Additionally, feral cats are present on the island, which may be predating upon this species; therefore, taking this all into account, it is conservatively suggested that the trends from before the eradication of sheep be used for this assessment. Thus the species would qualify as Endangered under criterion B1ab(ii,iii,v).
Comments are invited on these proposed categories and further information would be welcomed.
Ortiz-Alcaraz, A., Aguirre-Muñoz, A., Méndez-Sánchez and Ortega-Rubio, A. 2016. Feral sheep eradication at Socorro Island, Mexico: a mandatory step to ensure ecological restoration. Interciena 41: 184-189.
Rodriguez-Estrella, R., de la Luz, J. L. L., Breceda, A., Castellanos, A., Cancino, J. and Llinas, J. 1996. Status, density and habitat relationships of the endemic terrestrial birds of Socorro Island, Revillagigedo Islands, Mexico. Biol. Conserv. 76: 195-202.
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.