Global checklists
Anyone seeking information on the classification of birds will be confronted
with the fact that three major global checklists are available:
Outdated (Howard & Moore) or less popular alternative lists (TIF, Gaudin) are additionally available:
The primary focus of the checklists is on species and subspecies recognition, but the numbers of recognised species differ significantly among the lists (Neate-Clegg et al., 2021). Pairwise comparisons between selectable checklists are available on the Avibase website (link). Categorial ranks above species-level are largely identical in the checklists, but IOC waived "subfamilies" and "tribes". No checklist recognises "superfamilies".
Proposals to work towards a single world birdlist were debated at the International Ornithology Congress in Vancouver in 2018. As a result, the International Ornithologist's Union (IOU) established the Working Group Avian Checklists (WGAC), and the ambitious project appears to be making good progress. (link) The release of the unified global avian checklist (AviList) is planned for early 2025.
References
Collar NJ (2018), Taxonomy as tyranny, Ibis 160, 481-484. (pdf)
Conix S, Cuypers V, and Pence CH (2024), Measuring and explaining disagreement in bird taxonomy, Eur. J. Taxon. 943, 288-307. (pdf)
Garnett ST, Christidis L, Conix S, Costello MJ, Zachos FE, Bánki OS, Bao Y, Barik SK, Buckeridge JS, Hobern D, Lien A, Montgomery N, Nikolaeva S, Pyle RL, Thomson SA, van Dijk PP, Whalen A, Zhang ZQ, and Thiele KR (2020), Principles for creating a single authoritative list of the world’s species, PLOS Biol. 18, e:3000736. (pdf)
Gaudin J (2024), Inventaire taxonomique des oiseaux du monde, revu, augmenté et corrigé (Taxonomic checklist of Birds of the World, updated and corrected), 551 pages. (pdf)
Gaudin J (2024), La classification des oiseaux, à l’heure de la phylogénie moléculaire, 88 pages, unpublished. (link)
Neate-Clegg MHC, Blount JD, and Sekercioglu ÇH (2021), Ecological and biogeographical predictors of taxonomic discord across the world‘s birds, Glob. Ecol. Biogeogr. 30, 1258-70. (abstract)
Schweizer M, Marques DA, Olsson U, and Crochet PA (2023), The Howard & Moore complete checklist of the birds of the world: framework for species delimitation, Avian Syst. 1, 35-41. (pdf)