Proposal (83)
to South American Check-list Committee
Treat the
taxon semitorquatus as a separate species from Arremon taciturnus
Effect on South American CL: This
proposal would recognize two species within the taxon that we currently treat
as one, Arremon taciturnus.
Background: Arremon
taciturnus is widely distributed in tropical lowlands east of the
Andes. Its distribution extends southward along the Atlantic coast of Brazil to
n. Rio Grande do Sul. The population from Espírito Santo south has been treated
traditionally (e.g., Hellmayr 1938, Pinto 1944, Meyer de Schauensee 1970,
Paynter 1970, Ridgely & Tudor 1989, Sibley & Monroe 1990, Sick 1993) as
one of the four subspecies recognized within this species, A. t.
semitorquatus. Hellmayr and Pinto mentioned intermediate specimens from Rio
de Janeiro as evidence for intergradation between semitorquatus and
nominate taciturnus as evidence for their treatment as
conspecific.
The two taxa differ as follows: (1)
females of semitorquatus have an interrupted black chest band
like the males, whereas in nominate taciturnus, females lack a chest
band; (2) male semitorquatus have interrupted chest bands, whereas
those of nominate taciturnus are complete; (3) the sides and flanks
of semitorquatus are broadly gray, whereas those of nominate taciturnus
are narrower and a paler grayish; the mandible of semitorquatus is
yellow, whereas in nominate taciturnus it is black like the
maxilla; and (4) the shoulder area of the wing is the same color as the rest of
the dorsum in semitorquatus, but in nominate taciturnus, it
is conspicuously yellow.
New information: Raposo
and Parrini (1997) re-examined the distribution of the two forms on the
Atlantic coast of Brazil based on about 250 specimens, all from Brazil.
Although they did not look at the same specimens as Hellmayr, they found no
evidence for intergradation, and the only specimen with any hint of
intermediate characters, and that only in the extent of the chest band, was far
from the contact zone. They also pointed out that the specimens mentioned by Hellmayr
and Pinto also came from far south of the putative contact zone. Where the two
ranges abut in Espírito Santo and Minas Gerais, not only are there no signs of
intermediate specimens, but semitorquatus seems restricted to montane
areas and nominate taciturnus to lowlands (but small N). They concluded,
therefore, that their ranges were parapatric with no sign of gene flow and were
thus should be treated as two species.
Analysis: Raposo
and Parrini (1997) did not mention that the characters used to diagnose semitorquatus
from nominate taciturnus also vary among other subspecies in A.
taciturnus. For example, the extent of the breast band is variable even
within nominate taciturnus, the mandible of A. t. axillaris of
northern Colombia and Venezuela is all yellow, and the flanks of A. t.
axillaris are broad and dark as in semitorquatus (see
illustration in Hilty & Brown 1986); also, the females of other populations
show traces of the breast band. Thus, the importance of those characters in evaluating
how distinctive semitorquatus is minimized. What they should have
pointed out, however, is that semitorquatus is the only one of the four
taxa that lacks the conspicuous yellow shoulder.
Regardless with problems in the
comparative analysis, the fact remains that the evidence presented by the
authors indicates that these two taxa are parapatric, with no know geographic
borders between them, and behave as two species by any definition.
With no personal familiarity with
the contact region, and without any knowledge of the voices of semitorquatus vs.
taciturnus, I will make a plea for additional input from SACC members
and others.
Recommendation: I
tentatively vote YES on this one, pending input from others.
Literature Cited:
HELLMAYR,
C. E. 1938. Catalogue of birds of the Americas. Field Mus. Nat. Hist. Publ.,
Zool. Ser., vol. 13., pt. 11.
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.
PAYNTER, R.
A., JR. 1970. Subfamily Emberizinae. Pp. 3-214 in "Check-list of birds of
the World, Vol. 8" (Paynter R. A., Jr., ed.). Museum of Comparative
Zoology, Cambridge, Massachusetts.
RAPOSO, M. A., AND R. PARRINI. 1997. On the validity of the Half-collared
Sparrow Arremon semitorquatus Swainson, 1827. Bulletin Brit.
Orn. Club 117: 294-298.
RIDGELY, R.
S., AND G. TUDOR. 1989. The birds of South America, vol. 1. 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.
SICK, H.
1993. Birds in Brazil.
Van Remsen,
December 2003
P.S. - if anyone would like a
primitive pdf of the paper, just let me know.
____________________________________________________________________________________________
Comments from Zimmer: "YES.
In addition to the apparent parapatry of the two forms (without evidence of
intergradation), the vocal differences are impressive. In my experience,
nominate taciturnus typically gives a
series of 3 wiry, drawn-out notes, often preceded by some short
"tsit" notes (e.g. tsit tsit
tsizzzzz tsizzzzz tsizzzzz). These notes are distinctive in their thin,
scratchy (non-musical) quality, and never seem to tape record well (or, when
well-recorded, they never copy well!). I have noted similar vocalizations for
nominate taciturnus from several parts of its range ( e.g. se.
Venezuela, c. Brazil, ne. Brazil). On the other hand, semitorquatus typically
delivers two long notes (also commonly preceded by some faint "tsit"
notes), the first thinner and single-syllabled, the second, richer in tonal
quality, and distinctly two-syllabled (e.g. tsit
tsit seeeee soowheeeee). This song differs not only in pattern, but is of a
distinctly different quality that is easily differentiated by the human ear
(I'm guessing note shapes will look completely different in spectrograms). The
quality of the notes of semitorquatus is more musical, less harsh,
and is reminiscent of the quality of notes in the songs of many Thraupis
tanagers.
"Although the plumage
distinctions between the two taxa are not impressive, I would suggest that the
plumages of most recognized Arremon taxa are all just slight
variations on a common theme anyway. The vocal distinctions between semitorquatus
and taciturnus are comparable to those between taciturnus and
flavirostris, the latter of which is recognized by everyone as
specifically distinct, and, which occurs syntopically with taciturnus in
some areas of Brazil.
"This, combined with the
evidence presented by Raposo and Parrini regarding lack of intergradation and
parapatric distributions, is enough to convince me that we are dealing with two
species-level taxa."
Comments from Robbins:
"YES. After reading Kevin's comments about the vocalizations of semitorquatus,
I vote "yes" for separating it from Arremon taciturnus."
Comments from Stotz:
"YES. I would just note that our treatment of semitorquatus as a
separate unit in 'Neotropical Birds: Ecology and Conservation' was based on Ted
[Parker]'s knowledge of vocal differences in semitorquatus and
his sense that it was probably a different species."
Comments from Nores:
"YES. Estoy de acuerdo en separar Arremon
semitorquatus de taciturnus.
Las razones marcadas por Van me parecieron válidas, especialmente los hombros
amarillos, las cuales son fuertemente apoyadas por los comentarios de Kevin
sobre las vocalizaciones."