Proposal (96) to South American Classification Committee

 

Split Embernagra olivascens from E. platensis

 

[This proposal is based on the following publication:

Hayes, F. E. 2003. Geographic variation in the Great Pampa-Finch Embernagra platensis complex: evidence for two species. Ardeola 50:223-235.]

 

The Great Pampa-Finch (Embernagra platensis) of southern South America is represented by four subspecies belonging to two distinct groups occurring in allopatry: (1) nominate E. p. platensis in the east; and (2) E. p. olivascens, E. p. gossei, and E. p. catamarcanus in the west. I propose splitting E. platensis into two species: the monotypic Great Pampa-Finch, E. platensis, and the polytypic Olive Pampa-Finch, E. olivascens. The two groups approach each other closely in central Bolivia, western Paraguay, and central Argentina, but do not overlap (see Fig. 1 in paper). Intergradation between the two groups has been assumed by previous authors but never adequately demonstrated.

 

The olivascens group differs from platensis by the following six traits:

* averaging larger in size

* having a more strongly curved beak

* having a deeper orange beak

* having less extensive dusky colouration on the upper bill which is shaped differently

* lacking streaks or only faintly streaked on the back

* having a paler loral region, chin and abdomen.

 

Much overlap occurs in body size and shape, and even plumage (considerable variability in wear complicates any plumage analysis), but I found that the structure and coloration of the bill are the most diagnostic characters (see Fig. 2 in paper). To quantitatively assess the pattern of coloration on the bill, I measured the maximum height of pale coloration on the side of the bill. There was slight overlap among taxa in this measurement, but ALL specimens (including those misidentified, misplaced with the wrong taxon, or with questionable locality data) were unambiguously diagnosed to taxon based on the structure and pattern of coloration of the bill. No individual, including those in which the measurements overlapped, possessed intermediate traits.

 

The absence of clinal variation in the extent of pale bill coloration within each form (see Table 3 in paper) demonstrates that intergradation either does not occur or is potentially restricted to a narrow, still undiscovered contact zone in central Bolivia, western Paraguay, or north-central Argentina. Their apparent lack of sympatry could be attributable to competitive exclusion. Given the likelihood that bill structure and color, combined with other traits, may represent reproductive isolating mechanisms between the two groups, they could be considered specifically distinct. Further studies of vocalizations and genetics would be useful.

 

Floyd E. Hayes, February 2004

 

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Comments from Robbins: "NO. Although Hayes may prove to be correct, the lack of any vocal or molecular analyses leaves in my mind a question on whether platensis and olivascens deserve species status. Even Hayes seems uncertain on whether these two should be recognized as species when he states, 'I tentatively propose the recognition....'. If he is tentative then I see no reason why we should support the split until there is more information."

 

Comments from Zimmer: "NO. I'm with Mark on this on. The evidence sounds flimsy at best, and is lacking any information on voice. I see no reason to rush here, especially when Floyd also appears tentative."

 

Comments from Remsen: "YES. Although Floyd doesn't have all the pieces we normally require for allopatric taxa, he does have what I consider to be the only important one for parapatric taxa, those with a reasonable chance to exhibit free flow of genes, namely parapatry (or even perhaps sympatry in this case) without any sign of intermediacy where the two taxa come together. For me, this trumps any other indirect information."

 

Comments from Stiles: "NO. The evidence is suggestive  but in my opinion not conclusive, in part because the demonstration of "true" parapatry is not wholly convincing. The closest approach shown by specimens of the two putative species seems to be on the order of 100-300 km if I read the paper aright, and a lot could happen in that distance! I think that field work in the possible contact zones would be critical here, with use of vocalizations, morphometrics of specimens and if possible genetic evidence. In the absence of such information, I feel that this split is premature."

 

Comments from Nores: "NO. Pienso que las diferencias morfológicas no son demasiado importantes como para considerarlas especies diferentes. Aunque esto no aclara demasiado, vale la pena comentar que las dos subespecies se superponen (overlap) en Ucacha (Córdoba, Argentina) (Nores e Yzurieta 1980. Aves de ambientes acuáticos de Córdoba y centro de Argentina. Secr. Agr. Gan. Cba.)."

 

Comments from Jaramillo: "YES. I am convinced by Floyd's data that there is little or no intergradation between these two forms. Having a good deal of experience with the two groups, I have always thought they were rather different beasts and had in my mind that it was likely that two species were involved. Apart from the bill and plumage differences, the voices of the two do differ, although I don't know how useful that is in an oscine such as this. Furthermore, the habitats they take are quite different. Both are in open areas, but platensis is found in marsh, marsh edge, Pampas Grass thickets and other grass/reed dominated habitats. The olivascens group takes drier habitats, sometimes with Pampas Grass and open grassy areas but practically always with a dense shrub component.  One point I would like to make is that it disturbs me somewhat that what I am hearing from members is that molecular or voice data is now a 'must' for convincing that a split is warranted. Floyd's analysis is a traditional one, I hope that is not the problem. I can see concerns about needing more information from the potential area of contact and so forth, but that is an entirely different issue than suggesting that having voice and molecular data is some kind of a requirement for work like this to have weight. I would like to ask what voice data would really do in a situation such as this one where you have two allopatric oscine taxa, that have diverged enough to show structural and plumage differences. Wouldn't you just expect voice to differ in this situation? What would it be telling you that the data that Floyd has put forth not tell you? It is a very different situation than dealing with suboscines and various non Passerines, where we have good evidence that voice is hard-wired."