Proposal (343) to South American Classification Committee
Split Myiobius ridgwayi from Myiobius atricaudus
Effect on South American checklist: This would split Myiobius atricaudus into two species by splitting off the southeastern Brazilian taxon, ridgwayi.
Background: This is a companion proposal to the one regarding Myiobius barbatus. Like barbatus, various subspecies of atricaudus are scattered across the forested lowlands and foothills of the Neotropics from Costa Rica to eastern Brasil. There is substantial amount of geographic variation in plumage, but most of this variation is subtle. The one exception is the SE Brazilian subspecies ridgwayi, which is strongly buffy below, instead of yellow. It was treated as a separate species by Hellmayr (1927), although he acknowledges that it "is probably conspecific with M. atricaudus." Parker et al (1996) says that atricauda "probably contains 2 species." This refers to ridgwayi and reflects Ted's thinking as well as my own.
Analysis: There are no published data related to the potential specific status of ridgwayi. I can find no published data on voice that suggests its voice differs from other atricauda. Like other Myiobius, this is a generally quiet species. One other difference that applies to ridgwayi is, unlike the Amazonian populations, which are purely lowland forms, and apparently associated with varzea and secondary forests, ridgwayi is a foothills bird occurring from roughly 800 m up to about 1200 m, above the sympatric populations of Myiobius barbatus. Apparently, trans-Andean atricauda occurs from the lowlands up to 1000 m or higher, but is not strictly a foothills species, although it occurs in the foothills.
Recommendation: While ridgwayi is in my view the most morphologically and ecologically divergent taxon in either Myiobius barbatus or M. atricaudus, the absence of any serious data on voice or genetics makes it hard to seriously entertain the idea that this taxon should be split, so my recommendation is NO. However, if the committee votes to split any piece of Myiobius barbatus, it would make sense to strongly consider recognizing ridgwayi is a distinct species. In my view the only thing it lacks relative to sulphureipygius is a history of being considered distinct.
HELLMAYR, C. E. 1927. Catalogue of birds of the Americas. Field Mus. Nat. Hist. Publ., Zool. Ser., vol. 13., pt. 5.
PARKER, T. A., III, D. F. STOTZ, AND J. W. FITZPATRICK. 1996. Ecological and Distributional Databases, in D. F. Stotz, J. W. Fitzpatrick, T. A. Parker III, D. K. Moskovits, Neotropical Birds: Ecology and Conservation. University of Chicago Press, Chicago, IL.
Doug Stotz, April 2008
Comments from Remsen: "NO. Ted and Doug likely correct, but actual data are needed to cause a change to status quo."
Comments from Nores: "NO. Aunque considero que puede ser una especie distinta dado su colorido y distribución tan aislada, pienso que el criterio de Stotz de esperar por información de vocalizaciones o de análisis moleculares, es lo más prudente."
Comments from Stiles: "About the only differences between this case and the preceding one are that there is a clear status quo for not recognizing ridgwayi, but on the other hand there is a fairly clear ecological difference. Actually, this case might be more complicated - if my memory serves me, there is a distinctive form, considered a subspecies of atricaudus, in the tepuis of Venezuela that is also very buffy below. Someone should check this (does it look like ridgwayi and if so, what does this mean?), and it might be worth looking at the highest-elevation specimens of true atricaudus to see if there is any tendency towards buffiness. For the moment, I will hold off on this one."
Comments from Pacheco: "NO. Embora de minha perspectiva veja diferenças notáveis entre ridgwayi e os demais táxons subordinados à M. atricaudus e, portanto, boa chance de ser tratada como espécie, mesmo sob o BSC, prefiro aguardar uma análise formal da situação."
Comments from Pacheco: "NO. Need more data."