The ornithological world has 4 global checklists (as of early 2020). While 3 follow the results of peer-reviewed research at varying pace and conservatism, the HBW/BirdLife checklist, which is adopted by the global Red List authority, has implemented Tobias et al.'s (2010) 7-point scoring system to overhaul global ornithological treatment. Critically received in some academic quarters, this scoring system is lauded by other ornithologists for its simplicity and reproducibility, a claim that remains to be tested. We subjected 26 ornithologists to a set of 48 bird skins belonging to 20 controversial taxonomic complexes and observed a wide variance in scoring results, in most cases straddling anywhere from far below to above the species threshold of the 7-point rule and casting doubt on claims of high reproducibility. For a detailed assessment of genuine taxonomic discord, we compared the taxonomic coverage of the avifauna of the Indonesian Archipelago (comprising ∼1,400 species) between the HBW/BirdLife checklist, other major authorities, and the peer-reviewed literature. We detected that controversial treatments supported by the 7-point rule but at odds with the peer-reviewed literature predominantly refer to lumps, not splits, which are the usual subject of modern taxonomic quarrels. Notably, the method tends to unite morphologically (and sometimes vocally) cryptic forms into single larger species because of its inability to accommodate molecular and massive bioacoustic datasets that would indicate otherwise. On the other hand, the 7-point rule has produced numerous novel proposals for splits that may or may not be corroborated by future peer-reviewed inquiry. We recommend the 7-point rule as one of the multiple unofficial exploratory tools to flag cases of potentially cryptic species requiring further inquiry, but we advise against its adoption by other taxonomic authorities and the ornithological community.
LAY SUMMARY
Competing authorities continue to be in ample disagreement about birds' classification.
The checklist that Birdlife International applies to the global Red List is unique in that a standardized scoring system, the 7-point rule, was adopted to overhaul taxonomic treatments, often overturning the results of peer-reviewed research.
We explored the magnitude of conflict generated by application of the 7-point rule. Novel treatments disagreeing with peer-reviewed publications predominantly referred to “lumps,” with some cryptic forms united into single species because of the method's inability to accommodate molecular and massive bioacoustic datasets.
We also subjected 20 controversial cases to 7-point scoring by 26 ornithologists and observed a wide score variance, straddling from far below to above the 7-point species threshold and casting doubt on claims of high reproducibility.
We recommend against the adoption of the 7-point rule by taxonomic authorities, although it may continue to be a good informal approach to flag potential splits.