Proposal (342) to South American Classification Committee
Split Myiobius
barbatus into multiple species
Effect on South American checklist: This
would split Myiobius barbatus into two or three species.
Background:
SACC currently treats Myiobius barbatus as including sulphureipygius,
whereas the North American committee treats sulphureipygius as a
distinct species (AOU 1998). A form in southeastern Brazil (mastacalis)
is treated as a group that could be specifically distinct in several
references, and at least a couple I have seen say that it is sometimes treated
as distinct, but I have not found any references that actually do treat it as a
separate species (Actually Wikipedia lists mastacalis as a separate
species, but when you click on the common name (Yellow-rumped Flycatcher) it
takes you to an Asian species [more on that later]).
Hellmayr (1927) treated trans-Andean sulphureipygius as a
distinct species from barbatus. Zimmer (1939) concluded that "It
seems probable, therefore, that sulphureipygius and aureatus deserve
inclusion in the barbatus group." His main basis for this was, in
fact, the similarity between aureatus (the South American subspecies of
the sulphureipygius group) and mastacalis (the SE Brazilian
subspecies). He noted that aureatus and barbatus approached one
another without signs of intergradation. However, they are across a range of
Andes from one another. Since Zimmer there has been a diversity of treatments.
References treating sulphureipygius and barbatus as
conspecific include Hilty and Brown 1986, Meyer de Schauensee 1966, 1970, Pinto
1944, Ridgely and Tudor 1994, Sibley and Monroe 1990, Traylor 1979, Zimmer
1939.
References splitting barbatus and sulphureipygius as
separate species: Hellmayr and Cory 1927, Hilty 2003, Ridgely and Greenfield
2001, AOU 1983, 1998, Farnsworth and Lebbin 2004. Basically all of the Central
American literature back at least until Blake (1953) treats the two as separate
except for the 2nd edition of Birds of Panama (Ridgely and Gwynne 1989)
Analysis: There are really two current treatments that are widely applied.
Most South American literature lumps everything into barbatus, whereas
Central American literature splits out sulphureipygius. The almost 50/50
split in how these taxa are treated is a reflection of the fact that there is
essentially no data that support either treatment. Myiobius sulphureipygius
and M. barbatus are allopatric and show low levels of plumage and
morphometric divergence. They are not very vocal and most references either
don't mention voice or give a transcription that seems like it could be
interpreted as indicating that they sound the same. Overall the morphological
distinctiveness of trans-Andean sulphureipygius and eastern Brazilian mastacalis from
Amazonian barbatus seems roughly equivalent, so it would seem like treatment as
a single species or three species are the most logical option, although
historically the splitting of mastacalis has not been a common treatment
(or even a rare treatment?).
One weak piece of evidence that applies to the mastacalis/barbatus question
is that Traylor (1979) indicated that birds from western Mato Grosso are
intermediate between mastacalis and the subspecies insignis (part
of the barbatus group) of southeastern Amazonia. He suggested
that they might be intergrades between mastacalis and insignis.
I assume that this refers to two specimens discussed by Zimmer (1939), one of
which he assigns to insignis and the other, which he indicates
"agrees better with mastacalis," although it is unusually
large (for any Myiobius). Given that both these specimens are from
Amazonian drainages and mastacalis as far as I can tell is not even in
the Parana drainage, that these birds are really indicative of intergradation
between insignis and mastacalis seems doubtful to me.
One weak piece of evidence that might suggest splitting the taxa
within barbatus is the fact that barbatus and the very
similar atricaudus are broadly sympatric in all three major forest
realms. The Amazonian populations of these two species are very similar, such
that specimens have been routinely misidentified. The species tend to replace
one another in a patchwork; however, there are localities from which both
species are known. If these taxa act as distinct species, it might indicate
that the morphologically more divergent forms in Central America and eastern
Brazil would act as distinct species - maybe.
Recommendation: Ridgely (1976) treats sulphureipygius as
a distinct species. Later, Ridgely (Ridgely and Gwynne 1989 and Ridgely and
Tudor 1994) argued against treating sulphureipygius as distinct from barbatus
essentially because mastacalis is as distinctive as sulphureipygius.
However, Ridgely and Greenfield (2001) followed AOU (1998) in splitting sulphureipygius.
I find I agree with Ridgely--I really don't know what the best approach is. My
weak recommendation is to maintain all the forms as a single species given the
unimpressive morphological distinctiveness of all forms in the absence of vocal
or genetic evidence suggesting otherwise.
Proposal A to split sulphureipygius from barbatus. I
recommend a NO vote. If we maintain sulphureipygius as a subspecies of barbatus,
I will write a proposal for the North American committee to change their
treatment to a single species treatment, although I'm not sure I can see why
they would necessarily change. Note that if split, the English name
Sulphur-rumped Flycatcher would apply to sulphureipygius. Whiskered
Flycatcher is usually used for barbatus.
Proposal B to split mastacalis from barbatus. I recommend
a NO vote. If we split this, there is an English name issue. Meyer de
Schauensee (1966) suggested, with the three-species treatment, barbatus as
Whiskered Flycatcher, and Yellow-rumped Flycatcher for mastacalis.
However, Yellow-rumped Flycatcher is used for the Asian species Ficedula
zanthopygia. Its use for Myiobius mastacalis would seem like a bad
idea. Sibley and Monroe (1990) use Bearded Flycatcher for the barbatus group
and Whiskered for mastacalis. I would suggest that if we split this
complex, that we follow the English names use by Sibley and Monroe.
References:
AMERICAN
ORNITHOLOGISTS' UNION. 1983. Check-list of North American birds, 6th ed.
American Ornithologists' Union, Washington, D.C.
AMERICAN
ORNITHOLOGISTS' UNION. 1998. Check-list of North American birds, 7th ed.
American Ornithologists' Union, Washington, D.C.
BLAKE, E.
R. 1953. Birds of Mexico: A guide for field identification. University of Chicago
Press, Chicago, Illinois.
FARNSWORTH,
A. AND D. J. LEBBIN. 2004. Sulphur-rumped Flycatcher and Whiskered Flycatcher
accounts. Pp. 351-352 in "Handbook of the Birds of the World, Vol.
9. Cotingas to pipits and wagtails." (J. del Hoyo et al., eds.). Lynx
Edicions, Barcelona.
HELLMAYR,
C. E. 1927. Catalogue of birds of the Americas. Field Mus. Nat. Hist. Publ.,
Zool. Ser., vol. 13., pt. 5.
HILTY, S.
L. 2003. Birds of Venezuela. Princeton University Press, Princeton, New Jersey.
HILTY, S.
L., AND W. L. BROWN. 1986. A guide to the birds of Colombia. Princeton University
Press, Princeton, New Jersey.
MEYER DE
SCHAUENSEE, R. 1966. The species of birds of South America and their
distribution. Livingston Publishing Co., Narberth, Pennsylvania.
MEYER DE
SCHAUENSEE, R. 1970. A guide to the birds of South America. Livingston Publishing
Co., Wynnewood, Pennsylvania.
PINTO, O.
M. DE O. 1944. Catalago das aves do Brasil. Parte 2. Departamento de Zoologia
da Agricultura, Industria e Comercio, São Paulo, Brasil.
RIDGELY, R.
S. 1976. A guide to the birds of Panama. Princeton Univ. Press, Princeton, New
Jersey.
RIDGELY ,
R. S., AND P. J. GREENFIELD. 2001. The birds of Ecuador. Vol. I. Status,
distribution, and taxonomy. Cornell University Press, Ithaca, New York.
RIDGELY R.
S., AND J. A. GWYNNE. 1989. A guide to the birds of Panama, with Costa Rica,
Nicaragua, and Honduras (2nd ed.). Princeton Univ. Press, Princeton, New
Jersey.
RIDGELY, R.
S., AND G. TUDOR. 1994. The birds of South America, vol. 2. Univ. Texas Press,
Austin.
SIBLEY, C.
G., AND B. L. MONROE, JR. 1990. Distribution and taxonomy of birds of the
World. Yale University Press, New Haven, Connecticut.
TRAYLOR, M.
A., JR. 1979a. Subfamily Elaeniinae. Pp. 3-112 in "Check-list of birds of
the World, Vol. 8" (Traylor, M. A., Jr., ed.). Museum of Comparative Zoology,
Cambridge, Massachusetts.
ZIMMER, J.
1939. Studies of Peruvian birds, No. 30. Notes on the genera Contopus,
Empidonax, Terenotriccus, and Myiobius. American Museum Novitates
1042: 1-13.
Doug Stotz,
April 2008
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Comments from Remsen: "NO (both A and B). Until
actual data are presented for one or the other treatment, any classification is
largely arbitrary. As Doug recommends, I don't think we have a choice but to
stick with to status quo until those data appear."
Comments from Nores: "NO (both A and B). Pienso que como en la propuesta 343, lo más apropiado
será esperar por nuevas evidencias en vocalizaciones o análisis moleculares.
Además, sulphureipygius es más similar a mastacalis que a barbatus
(de acuerdo a los dibujos del HBW) así que de separa sulphureipygius debería también separar a mastacalis y
ponerlos en una misma especie, que en este caso tendría prioridad mastacalis.
Así que quedaría Myiobius mastacalis mastacalis y Myiobius mastacalis
sulphureipygius."
Comments from Stiles: "YES. This is, as Doug
notes, a tough one.. from my Central American-Colombian perspective, I would be
tempted to go the other way and vote YES on both - given the often subtle
differences in plumage among congeneric tyrannids, including the sympatric atricaudus
and barbatus in Myiobius itself plus the considerably greater
difference of sulphureipygius and the effective lack of a true
"status quo", I'd place the three (barbatus, mastacalis and sulphureipygius)
in a superspecies and hope that someone does the genetics and gets some good
vocal data soon! As Doug notes, the evidence is pretty tenuous whichever way
one goes, so my vote is decidedly sotto voce."
Comments from Pacheco: "NO to both A and B. Prefiro aguardar uma análise apropriada. As diferenças
morfológicas entre os táxons subordinados ao complexo M. barbatus são
menos abruptas que aquelas observadas no complexo M. atricaudus. É
sugestivo que J. T. Zimmer não tenha encontrado distinção entre um espécime do
"Rio Roosevelt" (interflúvio Madeira-Tapajós) e aqueles da Mata
Atlântica (M. b. mastacalis)."