Proposal (796) to South American Classification Committee

Recognize Colibri cyanotus as a separate species from C. thalassinus

Below is a proposal that I submitted to NACC, which was accepted and implemented by NACC last year. Although actual the split is extralimital to the SACC area, it affects SACC in that NACC now treats “our” species under a different species name and English name, i.e. Green Violetear, C. thalassinus, is now Lesser Violetear, C. cyanotus, in the NACC classification.

The vote for SACC is in two parts, for both of the rationale is outlined in the NACC proposal and for both of which I recommend a YES:

A. Recognize the split of South American (and s. Central American) taxa as a separate species, Colibri cyanotus, from extralimital northern Middle American taxon, Colibri thalassinus.

B. (for English name voter subgroup): If YES on A, then change the English name of our Green Violetear to Lesser Violetear.

Van Remsen, June 2018

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Recognize Colibri cyanotus as a separate species from C. thalassinus

Background: There are three currently recognized species of Colibri violetears that are mostly green: C. coruscans (Sparkling Violetear), C. thalassinus (Green Violetear), and C. serrirostris (White-vented Violetear). The species are very similar in plumage and differ primarily in extent of violet on throat and belly:

The problem, as can be seen in the photos, is that C. thalassinus, as circumscribed since Peters, consists of two subspecies groups, both of which occur in the NACC area, and one of those, nominate thalassinus, looks more like C. coruscans, and the other group looks more like C. serrirostris.

New information: Remsen et al. (2015) proposed that species limits in the Colibri thalassinus group be revised. Here is the text:

“Colibri thalassinus. As defined for most of the last 75 years (Peters 1945, Schuchmann 1999, Dickinson & Remsen 2013), this species consists of several subspecies found in montane areas from central Mexico to northwestern Argentina. The subspecies fall into two groups (Dickinson & Remsen 2013): (1) nominate thalassinus from Mexico to Nicaragua, and (2) the cyanotus subspecies group, which consists of the subspecies cabanidis of Costa Rica and W Panama, and cyanotus and other subspecies of South America. These two subspecies groups differ from each other in plumage nearly as much as the green species of Colibri differ from each other. Nominate thalassinus, from Mexico to Nicaragua, is more like South American C. coruscans in its conspicuous blue coloration in the ventral plumage than it is to the Central and South American subspecies group, in which blue is absent (group of AOU 1998, Dickinson & Remsen 2013). Nominate thalassinus has a faint line of blue that connects the blue face patches across the chin, also suggesting the broader blue across the chin of coruscans; the Central and South American subspecies group has the chin completely green. The two subspecies groups were formerly treated as separate species (Ridgway 1911, Cory 1918), but Peters (1945) treated them as conspecific without providing any rationale. Our sampling included only C. t. crissalis of the cyanotus group, and we were thus unable to determine whether broadly defined C. thalassinus is monophyletic. Even if monophyletic, field studies of the vocalizations and behavior in this group of taxa would illuminate whether two or more species should be recognized within C. thalassinus under the Biological Species Concept. Because nominate thalassinus differs in plumage and size from the cyanotus subspecies roughly to the same degree as other taxa ranked as species within Colibri, we consider that the burden-of-proof falls on treating them as conspecific and propose that nominate thalassinus and the cyanotus group should be treated as separate species until data indicate otherwise.”

Analysis and Recommendation: Our argument was that the species limits prior to Peters should be restored given that (1) Peters did not present any explicit rationale, and (2) nominate thalassinus is closer in plumage to C. coruscans, which is clearly a separate species (partially sympatric) from South American thalassinus populations and therefore nominate thalassinus should also be treated as separate from the cyanotus group. Also, the cyanotus group is actually closer in plumage to Colibri serrirostris than to nominate thalassinus. This is a weak argument, of course, but the idea is to return to the species limits of Robert Ridgway until better data allow a more modern evaluation (e.g., analysis of voice and display). So, I recommend a YES on this. Reasons to vote NO would include retaining status quo until better data available (e.g., comparative genetic distances and vocal data).

English names: If this passes, I recommend a return to the names used by Ridgway, i.e. Mexican Violetear for thalassinus and Lesser Violetear for the cyanotus group. “Mexican” is not ideal because its range extends to Nicaragua, but thalassinus is often referred to as “Mexican Green Violet-ear”. “Lesser” is insipid, but appropriate because it is the smallest species in the genus; this also resurrects a name for the daughter species of the split, thus restricting use of “Green Violetear” to a broadly defined thalassinus.

References:

REMSEN, J. V., JR., F. G. Stiles, & J. A. McGuire. 2015. Classification of the Polytminae (Aves: Trochilidae). Zootaxa 3957: 143-150.

Van Remsen, January 2016

Comments from Remsen: “A: YES”

Comments from Stiles: “YES. Plumage and size differences from nominate thalassinus indicate that cyanotus should be accorded species rank, especially as no rationale for their lumping by Peters was given.”

Comments from Areta: “YES. The dramatic differences in plumage, with thalassinus resembling coruscans more than cyanotus, while cyanotus resembles serrirostris, strongly indicate that cyanotus deserve separate species status.”

Comments from Claramunt: “NO. It is a weak argument and, at least in the series we have at the ROM, the differences between thalassinus and cyanotus are not as great as in the LSU synoptic series: 1) the ventral blue stripe in thalassinus is small and diffuse and some cyanotus from Costa Rica have a tinge of blue; 2) dorsal parts of thalassinus are identical as those of cyanotus, both more coppery than in coruscans; 3) the throat in thalassinus is mostly green like in cyanotus except for one or two rows of blue feather on the chin, nothing approaching the blue gular patch of coruscans, nor its bluish green breast. Overall, thalassinus is more similar to cyanotus than to coruscans, and it remains to be demonstrated that the subtle differences between thalassinus and cyanotus are diagnostic. Surprised that NACC was so liberal on this.

Comments from Robbins: “YES. Yes to recognize as a species. If I were voting on English names I would be fine with calling it Lesser Violetear.”

Comments from Zimmer: “A. YES. It may be a “weak argument”, but I’d argue that it’s still based upon firmer ground than the lump by Peters. More data (genetic and vocal) is pretty clearly called for, but until we have such data, I would say that the plumage and biometric distinctions between the two subspecies groups, particularly within the context provided by the “yardstick” comparison with other recognized species of green Colibri, puts the burden of proof on those who would argue for maintaining the unsubstantiated Peters lump.

B.: “YES. Mexican” and “Lesser” make sense as English name modifiers.”