Interaction between the 2 Subspecies Groups of the Seed-Finch Sporophila Angolensis in the Magdalena Valley, Colombia

The Lesser or Thick-billed Seed-Finch {Sporophila angolensis) is a medium-sized, heavy-billed neotropical finch ranging from southern Mexico to Argentina. Although it is usually placed along with 5. crassirosiris and S. maximiliani in a separate genus, Oryzoborus, I have given reasons elsewhere for synonymizing Oryzoborus with Sporophila and have also discussed subspccilic variation in S. angolensis (Olson in press). Within 5. angolensis there are two subspecies groups, long considered separate species, that differ in the adult male plumage. In the funérea group, found from southern Mexico through Middle America to Colombia and Ecuador west of the Andes, the adult males are entirely black below, whereas in the angolensis group, found in most of tropical South America east of the Andes, the belly and ñanks are deep chestnut, sharply contrasting with the black breast. The nature of the interaction between these two subspecies groups has hitherto not been understood. Meyer de Schauensee (19S1: 1094) noted adult male specimens oí funérea from Guatemala, Honduras, Panama, and the Santa Marta region of Colombia that had "traces to a considerable amount of chestnut on the belly, clearly showing their affinity to O. angolensis. " Wetmore (19S7: 103) preferred to regard the two forms as separate species, and he considered the exceptional specimens oi funérea as expressing a "deep-seated character that indicates ancient relationship to angolensis through some common ancestral stem. " As evidence, he cited the fact that the aberrant birds appeared to occur at random rather than being "restricted to the area where the two styles of color pattern are in contact. " In revising the subspecies of 5. angolensis, I examined most of the specimens available in North American museums. Apart from birds taken in the Magdalena Valley and the Santa Marta region, Colombia, I found that almost all of the adult male specimens of funérea that showed some chestnut in the belly were individuals that retained feathers from the preceding subadult plumage, Subadult males are more intensely colored than females, and some of the subspecies (e.g. salvint and aethiops) are quite chestnut in the female and subadult plumages, so that any of these feathers retained in the definitive male plumage would appear to be nearly as chestnut as in the angolensis group. I have seen only one specimen from outside the Magdalena Valley and Santa Marta in which the chestnut intermingled with black did not appear to be retained from the subadult plumage (USNM 449335, Soná, Veraguas, Panama). Even an occasional female specimen in the funérea group may have a sprinkling of decidedly chestnut feathers in the belly (e.g. USNM 403899, Valdivia, Antioquia, Colombia; CM 42219, Minea, Santa Marta, Colombia). There are specimens from the Magdalena Valley, however, that I regard as definite intergrades between the angolensis and funérea subspecies groups. In these birds the black belly is distinctly suffused with chestnut, sometimes to the extent that the pattern of the angolensis group may be discerned, as noted by Meyer de Schauensee (1951). The distribution of these intergrades is of considerable interest (Fig. 1). Birds from the north side of the Santa Marta mountains at Chirua, La Concepción, and Pueblo Viejo are intergrades, whereas those from the western side, at Minea, are entirely black. A definite intergrade from the vicinity of San Gil, Santander is from a rather high elevation (between 500 and 1,000 m) in the valley of the Rio Fonce, which ultimately flows into the Rio Sogamosa, a tributary of the Magdalena, A bird from Ayacucho, Magdalena is likewise an intergrade, whereas those somewhat farther up the Magdalena Valley in Santander (Azufrada, Infantas, El Centro, Hacienda Santana) are all black, as is typical of the funérea group. Olivares (1969) records two specimens of this species from Cundinamarca (at Puerto Salgar and La Vega) that he referred to funérea, as one specimen was an entirely black adult male. It is not clear from which locality this specimen was taken and therefore the occurrence is not shown in Fig. 1. Of considerable interest is the population from the upper Magdalena Valley in Huila (La Plata) and Toliraa (Melgar), known so far only from two specimens. These birds belong to the angolensis group, although the chestnut underparts are a much grayer, more chocolate-brown, for which reason I have designated this population as a separate subspecies (Olson in press). This is the only population of the angolensis group known from west of the eastern Andes. Although the lack or paucity of specimens from critical areas hampers any reconstruction of the past history of the two subspecies groups, two hypotheses suggest themselves. Sporophila angolensis is a