Proposal (#379) to South American Classification Committee

Recognize Trogon chionurus as a separate species from Trogon viridis (2)

Effect on SACC: This would treat an existing species, Trogon viridis, into two species.

Background: Our current SACC note is as follows:

2. Ridgely & Greenfield (2001) considered the subspecies chionurus of the Chocó region to be a separate species from Trogon viridis; followed by Hilty (2003); SACC proposal to recognize this split did not pass because of insufficient published data. Genetic data (DaCosta & Klicka 2008) suggest that chionurus is more closely related to T. bairdii than either are to Amazonian T. viridis. Proposal needed. Sibley & Monroe (1990) considered Trogon viridis to form a superspecies with Central American T. bairdii, and suggested that they might be conspecific. Proposal needed.

See SACC proposal 49 for a summary of previous arguments pro and con. A one-sentence summary of the previous arguments might be although chionurus differs from viridis in voice and plumage, the vocal differences have not been adequately quantified or documented (in fact, published descriptions are contradictory). You can here samples of both at Xeno-Canto – I am impressed with the differences in rhythm: chionurus and viridis (but I also hear lots of variability – browse Trogon viridis.

New information: DaCosta & Klicka (2008) published a gene-based phylogeny of the genus that included samples of bairdii (2), viridis from Amazonia (12), and chionurus from W. Ecuador and Panama (2). They sampled 1 mitochondrial gene, ND2, and 1041 base pairs, of which 557 were phylogenetically informative. They found strong support (99% maximum likelihood bootstrap, 100% Bayesian support) for the sister relationship between chionurus and bairdii, as well as strong support for Amazonian viridis as the sister to these two. See Prop. 378 for tree.

Analysis and Recommendation: With genetic support from only a single, mitochondrial gene as the basis for the relationship, one could argue that the tree is only a gene tree, not a species tree, or that the bairdii-chionurus relationship is due to incomplete lineage-sorting, or even that hybridization between bairdii and chionurus produces the result. Nonetheless, combined with the qualitative vocal data, I think that published evidence is sufficient for a change in species limits, so I tentatively recommend a YES.

Literature Cited:

DaCOSTA, J. M., AND J. KLICKA. 2008. The Great American Interchange in birds: a phylogenetic perspective with the genus Trogon. Molecular Ecology 17: 1328-1343.

Note on English names: Ridgely & Greenfield (2001) coined “Western White-tailed Trogon” for chionurus and “Amazonian White-tailed Trogon” for viridis, and this was followed by Hilty (2003) and Gill & Wright (2006). I think that represents a degree of establishment that justifies starting with them as “status quo” if the proposal passes. However, Cory (1919) restricted White-tailed to chionurus and called viridis “Green-backed.” These are actually very nice names. “Chionurus” means “snow-tailed”, and the larger amount of white in the tail of chionurus is one of the differences between the two taxa; and there is also the nice parallel between the English and scientific names. “Green-backed” also points to another major plumage difference between the two (blue back in chionurus) and is also reflected, somewhat, in the scientific name viridis. Also, those long compound names are fairly unpopular, despite their ability to imply relationships. And in this case, with bairdii likely the sister to chionurus, they are actually misleading as to relationships. Finally, “Western” and “Amazonian” are fairly insipid and not entirely accurate because a highly disjunct population of viridis is found in the Atlantic Forest region. Therefore, I propose we use these shorter, more accurate, more venerable names as the status quo (therefore requiring a proposal the longer compound names could be instituted by proposal), but I’d like to take a poll of our English-first members to see if they like this.

Additional Note on English names (added 6 May 09): Frank Gill pointed out to me that the illustrations in Ridgely & Gwynne (1989), Ridgely & Greenfield (2001), and HBW show chionurus as having a bright green back. This is evidently an error. Our recent specimens from Panama have unambiguously violet-blue backs, as illustrated correctly by Restall et al. (2006). Wetmore (1968) indicated that some individuals may have green in the center of the back, but I cannot find any evidence for all-green backs.

Van Remsen, November 2008

Comments from Zimmer: “YES. Vocal distinctions between these two have been noted for some time, and there are plenty of qualitative descriptions out there, as well as published and internet-searchable examples of recordings. These agree well with the DaCosta & Klicka genetic data, which places chionurus as closer to bairdii, a relationship that would have been predicted on vocal and morphological characters alone. I think Van’s suggestions regarding English names (“White-tailed” reserved for chionurus, and “Green-backed” for viridis) are excellent.”

Comments from Robbins: “YES, again web-based vocal data support the Klicka et al. genetic conclusions. I fully support Van’s English name suggestions.”

Comments from Stiles: “YES, for reasons stated by Van and Kevin. I also prefer the English names suggested by Van – I dislike three-word monsters, hyphenated or not, if simpler alternatives are available.”

Comments from Nores: “YES. Los datos morfológicos, genéticos y de vocalizaciones indican que chionurus es una especie diferente de T. viridis. Sin embargo, me parece poco probable que esté más cerca de T. bairdii que de T. viridis. Pienso que debe tratarse de un problema relacionado con haber usado un solo gen mitocondrial, como ha sido destacado por Van. Como en Xeno-Canto no hay vocalizaciones de T. bairdii no pude comparar con las otras especies.”

Comments from Stotz: “YES. I favor Van's English names.”

Comments from Jaramillo: “YES – Song, morphology and genetics all line up to clarify the relationship here. Kudos to Van for suggesting some simple names, rather than multi-word monsters, so yes Green-backed and White-tailed work well!

Comments from Pacheco: "YES. Os dados disponíveis bem corroboram a proposta.”