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
________________________________________________________________________________________
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.”