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.
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."