Proposal (#287) to South American Classification Committee


Recognize four species of Sporophila within the Sporophila americana superspecies

This proposal would change our current list in two respects: it would place S. intermedia (Gray Seedeater) between S. corvina (Variable Seedeater, previously called S. aurita) and S. americana (Wing-barred Seedeater); and would recognize as a species distinct from the latter S. murallae (Caquetá Seedeater). The detailed justification for this treatment is presented in Stiles (1996); I summarize the main arguments here.

Classification of Sporophila seedeaters has in the past largely been based upon the coloration of the adult males; in particular, among the species of Central and northern South America, two main species groups have been recognized with male plumage being mostly gray vs. black-and-white. In this paper I argue that a close relationship exists between a black-and-white species (corvina) and a gray species (intermedia), based upon previously unappreciated similarities in plumage pattern, plumage sequences, distribution, biometrics and two localized zones of at least sporadic hybridization involving different races of both species. S. intermedia and americana are apparently parapatric in coastal NE Venezuela and W Guyana and appear to replace each other on Trinidad and Tobago, suggesting that they are too similar ecologically to coexist. No hybrids are known between these two, and they appear less closely related than intermedia is to corvina based on plumage pattern. The range of americana continues along the coastal lowlands of South America to the mouth of the Amazon and thence eastward along the Amazon (and apparently one or more of its northern tributaries in E Brazil) to the region of Manaus; Amazonian birds may differ in plumage from those of the coastal regions and have been named as a separate subspecies dispar, although this has not been accepted by all authors. Separated from this population by ca. 500 km is murallae, an isolated upper Amazonian derivative of americana. This form had been considered intermediate between corvina and americana by Meyer de Schauensee (1952) and this was used by some authors, notably Olson (1981) to lump corvina with all its races into americana. I demonstrate that this is incorrect, and that except for its lesser development of wing-bars there is no justification for allying murallae with corvina; in numerous features its affinities clearly lie with americana. However, it differs from americana in several plumage characters (and more from the Amazonian populations of the latter, if the characters of dispar are correct). It also differs most strikingly in biometrics, such that I consider it less close to americana than corvina is to intermedia, and thus deserving of species rank. These four should be placed in the following order in our list: corvina, intermedia, americana and murallae.

Considering all of these forms as a single superspecies appears justified based on the overall distribution of all forms. At the center of the distribution is intermedia, with the black-and-white forms occurring around the periphery, generally in areas of higher rainfall (as might be expected by Gloger's rule). No member of this group appears to occur on the Guyana shield.

I note in passing that, as Olson had earlier suggested, the name aurita is unidentifiable as its type came from the stable hybrid swarm between the races corvina and hicksii. The type has disappeared, and it is impossible to assign this name to either of the parental populations. The oldest name in this group that clearly refers to a definite population is corvina; hence the Variable Seedeater should be called S. corvina. (Olson did not do this as he considered all the black-and-white forms to be races of americana). I also note that Dickinson and Ridgely & Greenfield recognize murallae as a species separate from americana. I recommend a YES vote on this proposal.

References:

Meyer de Schauensee, R. 1952. A review of the genus Sporophila. Proc. Acad. Natl. Sci. Phila. 104:153-196.

Olson, S. L. 1981. The nature of variability in the Variable Seedeater of Panama. Proc. Biol. Soc. Wash. 94:380-390.

Stiles, F. G. 1996. When black plus white equals gray: the nature of variability in the Variable Seedeater complex (Emberizidae: Sporophila). Orn. Neotrop. 7:75-107.

Gary Stiles, June 2007

 

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Comments from Robbins: "YES for now in recognizing four species within the Sporophila americana complex. I would like to see a molecular data set, not only for this group but for all of Sporophila, before I become fully convinced of species limits within this complex."

Comments from Zimmer: "YES. A confusing group to be sure, but Gary's arguments are convincing."

Comments from Nores: "YES, aunque no muy covencido. Este es un caso en el cual un análisis molecular sería fundamental. Además, Ridgely y Tudor señalan que las vocalizaciones de todas las poblaciones son similares."

Comments from Jaramillo: "YES - Although I imagine that eventually we may have some more re-shuffling in this genus. I concur with others that this genus is screaming out for a molecular analysis."

Comments from Pacheco: "YES. Estou ciente das dificuldades do complexo Sporophila americana; todavia, entendo que o arranjo proposto por Gary é melhor que o tradicional."