Proposal (45) to South American Classification Committee
Change Myrmotherula
brachyura to Myrmotherula ignota
Background: Griscom (1929) described an antwren
from eastern Panama as Myrmotherula brachyura ignota, considering it to
be conspecific with the widespread Amazonian form Myrmotherula brachyura.
Since then ignota has been found west of the Andes from Panama to northwestern
Ecuador. Later, Zimmer (1932) concluded that within the Amazonian specimens
called brachyura, there was another species hidden, which he called Myrmotherula
obscura. It is broadly sympatric with brachyura across northwestern
Amazonia. All three of these taxa are very similar, differing primarily in the
relative proportion of black vs. white in the black-and-white streaking that
dominates the plumage. It is routine that specimens of obscura and brachyura
are confused in collections. Bond (1950) noted the similarity in plumage
between ignota and obscura, suggesting that they were more
similar to each other than either is to brachyura. Later authors,
including AOU (1998), have retained ignota as conspecific with brachyura
but noted that it might be a distinct species, or belong with obscura.
Ridgely and Greenfield (2001) considered ignota a distinct species.
Previous Evidence: Ridgely and
Greenfield (2001) in splitting ignota note vocal differences from brachyura,
and comment that its song "closely resembles Short-billed Antwren's
song."
New evidence: Isler and Isler (2003) analyzed both
morphology and voice of ignota, brachyura and obscura. In
both male and female plumage, all are very similar, with ignota more
like obscura than brachyura, and in fact more distinctive than obscura
is when compared to brachyura. M. obscura has a significantly
shorter bill than brachyura (responsible for its English name
Short-billed Antwren). The bill measurements of ignota are intermediate
but closer to brachyura (although samples are small) . No other measurement
data are provided.
Although plumage data suggest that ignota
might be closer to obscura than to brachyura, the voice data are
much more compelling. The loudsongs of ignota and obscura are
very similar, and I daresay impossible to distinguish. Myrmotherula
brachyura while grossly similar to the other two taxa, differs in the
number of notes, in pace (faster), and in acceleration (the song speeds up in
the last half of the song dramatically, almost becoming a roll, while the pace
increases only slightly in the other two). Additionally, a common call note of brachyura
differs substantially from the other two, which share a similar call.
Proposed change: This proposal suggests
that ignota be removed from Myrmotherula brachyura and considered
conspecific with Myrmotherula obscura. As ignota has priority,
the species should be called Myrmotherula ignota. There are three
possible English names for Myrmotherula ignota. The name Griscom's
Antwren has been suggested for ignota (sensu stricto) by Meyer de
Schauensee (and is used by Ridgely and Greenfield 2001), and Short-billed
Antwren is well established for Myrmotherula obscura. The Islers suggest
the name Moustached Antwren for the combined taxon in recognition of the
stronger black malar mark that is characteristic of both ignota and obscura
and is perhaps the best field plumage character.
Recommendation: I recommend following
the Islers and treating Myrmotherula ignota and M. obscura as
conspecific under the name Myrmotherula ignota. I also recommend
following the Islers in the use of Moustached Antwren for Myrmotherula
ignota. The other two names have always been applied to the component
subspecies of ignota separately. Short-billed is much less appropriate
when ignota is included with obscura. As for Griscom's Antwren,
the Isler's rightly note it was Zimmer who really gave us the first
understanding that there were multiple taxa in this group. Griscom did not
recognize his bird as deserving of specific status, treating it as conspecific
with brachyura and providing only a brief description. So despite my
opposition in general to new English names, I think this lump merits a new one.
References:
American Ornithologists' Union. 1998. Check-list of North American Birds. 7th
edition. American Ornithologists' Union, Washington, DC.
Bond, J. 1950. Notes on Peruvian Formicariidae. Proc. Acad. Nat. Sci. Philadelphia 102: 1-26
Griscom, L. 1929. A collection of birds from Cana, DariƩn. Bull. Mus. Comp. Zool. 69: 149-190.
Isler, M. L. and P. R. Isler. 2003. Species limits in the pygmy antwren complex (Aves: Passeriformes: Thamnophilidae); 1. The taxonomic status of Myrmotherula brachyura ignota. Proc. Biol. Soc. Wash. 116: 23-28.
Ridgely, R. S. and P. J. Greenfield. 2001. The Birds of Ecuador. Vol. II. Field Guide. Cornell Univ. Press, Ithaca, NY.
Zimmer, J. T. 1932. Studies of Peruvian birds.
III. The genus Myrmotherula in Peru, with notes on extralimital forms,
part 1. Amer. Mus. Nov. 523: 1-19.
Doug
Stotz, July 2003
______________________________________________________________________________________
Comments
from Remsen: "if
only we had this amount of information for all such decisions ... . In my
opinion, the Islers have made a strong case for ignota and obscura
being sister taxa and that obscura is best treated at the subspecies
rank (which for me is a diagnosable taxon that has not diverged to the level
associated with differences know to be associated with cessation of gene flow
in related taxa that are parapatric or sympatric). I'll also go with
'Moustached' if, as I assume, that is the name to be used in forthcoming HBW
vol 8."
Comments
from Schulenberg:
"Change Myrmotherula brachyura to Myrmotherula ignota
[except that I think the vote is to change both Myrmotherula obscura and
Myrmotherula brachyura ignota to Myrmotherula ignota]. My vote is
"Yes": the Isler and Isler paper makes a strong case.
"Moustached Antwren" will take some getting used to, but is
acceptable. "
Comments
from Zimmer: "I
vote "yes" on the proposal to recognize Myrmotherula ignota as
specifically distinct from M. brachyura, but as belonging with M.
obscura. The rationale for this change is well-documented by the Islers,
and it is what we have followed for the HBW treatment. I also favor the Islers'
suggested English name of "Moustached Antwren". "Short-billed
Antwren" makes no sense with the inclusion of ignota (especially
since ignota has priority within the ignota/obscura
complex), and "Griscom's Antwren" is tainted by published statements
that it should be split from brachyura (without recognizing that it
belonged with obscura). "Moustached Antwren" highlights one of
the more noticeable field marks, so I favor this suggested name."
Comments from Robbins: " I vote "yes" to considering ignota and obscura as conspecific and applying the English name "Moustached" The Islers did an excellent job of documenting the rationale for these changes."
Comments from Silva: "No. In fact, my proposal is that the Isler's data are indicating that ignota, obscura and brachyura are distinctive species. If ignota is distinct in plumage from obscura but not in voice, it must have specific status as well because different characters have different rates of evolution and one cannot expect to find in nature biological species presenting differences in both plumage and voice."