V1, V2:

The treatment of species is as per Jetz et al. (2012) and follows the Birdlife V3 world list (June 2010, 9,895 extant species recognized). Of Birdlife V3 we did not recognize nine species (Anodorhynchus glaucus, Gallinula pacifica, Gallirallus lafresnayanus, Oceanodroma macrodactyla, Ophrysia superciliosa, Rhodonessa caryophyllacea, Siphonorhis americana, Tadorna cristata, Vanellus macropterus) that are widely considered extinct and three (Heliangelus zusii, Atlapetes blancae, Upupa marginata) that are considered not valid by most authorities (resulting in 9,882 accepted species). In addition to Birdlife V3 we recognize 111 species that are considered valid by the Handbook of the Birds of the World (del Hoyo et al. 1992-2011) and/or Birds of the Western Palearctic (Cramp et al. 1978-1994) and/or Birds of Africa (Urban et al. 1986-2000) and that are also recognized by IOC world list V2.7 (Dec 29, 2010), resulting in a total of 9,993 recognized species. Our species lists and taxonomic information is provided in Table S2. We updated the threat categories of the Birdlife V3 list with the 2012 assessment data (based on Birdlife V5; 225 species changed threat status compared to 2010). Birdlife taxonomy V5 recognizes 9,935 extant species compared to 9,895 in V3. 45 additional species not considered extinct were reviewed in Birdlife V5 compared to V3. Of these 4 were new discoveries and 41 were splits from species in V3.

Jetz, W., G. H. Thomas, J. B. Joy, K. Hartmann, and A. O. Mooers. 2012. The global diversity of birds in space and time. Nature 491:444-448.