Eliminate Sporophila insulata from the list of South American birds

Proposal (245) to South American Classification Committee

Eliminate Sporophila insulata from the list of South American birds

The Tumaco Seedeater, Sporophila insulata, was one of the continent's least-known birds: from the collection of the type series in 1912 on Tumaco Island in extreme SW Colombia until 1994, when Salaman & Giles discovered a breeding population on Isla Bocagrande near Tumaco, the bird was never seen by an ornithologist despite several searches, and acquired "critically endangered" status on the ICBP list (Collar et al. 1992). According to Salaman (1995), the birds were breeding concurrently with S. telasco on the island, although he adduced some spatial separation between the two. In March 1995 I visited the site and found seedeaters in postbreeding flocks from which I collected three males that varied in plumages, seeing others that apparently ran the gamut between nearly wholly chestnut underparts and nearly wholly white, with chestnut only on the chin (and were thus identical to telasco) in the same flocks. Although Chapman (1921) compared his insulata only with S. minuta with its rufous underparts in the adult males (a species not then known from the Pacific slope), Ridgely & Tudor (1989) noted several similarities between the type series of insulata and S. telasco, and suggested that the latter might be the closest relative of insulata, or that insulata might even represent a hybrid between telasco and minuta. I therefore proceeded to study plumages and plumage sequences in telasco and minuta to compare these with the type series of insulata and my specimens. I found that insulata agreed closely with telasco in morphological measurements and plumage, differing only in the much greater extent of chestnut below. The plumage sequences were also similar: evidently the chestnut is acquired by the males early, and the changes toward the definitive plumage occur mainly in the dorsal tracts. I therefore concluded (Stiles 2004) that insulata represented a color phase, or at best a race, of telasco. More recently my student Juan Carlos De Las Casas made more extensive collections of both telasco and insulata in W Nariño and NW Ecuador, and performed a genetic analysis (cytochrome B) that showed that insulata was genetically indistinguishable from telasco but quite different from minuta. He also discovered a breeding population of minuta on the Nariño coast, thus raising the possibility that insulata might indeed represent a hybrid between this species and telasco, with the latter being the female parent (De Las Casas in prep: see De Las Casas 2004 for a summary). Although the range of plumage types represented in the specimens and observations of insulata seems better explained by insulata representing a mutant phenotype within telasco than by a single hybridization event (or repeated mixed matings with telasco always the female parent), the question remains to be resolved. However, in either case insulata does not represent a species taxon and should be struck from the list of bird species of South America. I therefore recommend a YES vote on this proposal.

References

Chapman, F. M. 1921. AMNH Novitates 18:1-12.

De Las Casas, J. C. 2004. Summary of thesis in Ornitología Colombiana 2:68.

Ridgely & Tudor 1989: The birds of South America, vol. 1.

Salaman, P. G. W. 1995. Cotinga 4:33-35.

Stiles, F. G. 2004. Ornitologia Neotropical 15:17-30.

Gary Stiles, September 2006

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Comments from Cadena: "YES. Gary's analyses of morphology and plumage are quite convincing and are backed up by the as yet unpublished genetic data of De las Casas. It is worth noting, however, that work on the capuchinos group of Sporophila has shown that good species in this genus are not distinct in mtDNA, so interpreting the genetic data at hand is not as straightforward as one would hope. It's kind of sad to lose a Colombian endemic, but S. insulata has to go... "

Comments from Robbins: "YES. Gary convincingly demonstrates that Sporophila insulata does not merit species status."

Comments from Jaramillo: "YES - However, the whole thing strikes me as odd and needing more research. It seems odd that the morph would differ so strikingly on what I imagine is a highly sexually selected trait (rufous plumage in telasco). You would think this would fix pretty quickly due to female choice? Maybe telasco keeps invading from the mainland? An interesting issue, but given the available data it does seem that accepting insulata as a species is not supported."

Comments from Remsen: "YES. Burden of proof is now on treating insulata as a valid species. This genus is peculiar in the plasticity of plumage types and the tendency for interspecific hybridization, and the demise of insulata should be only the first of many changes to traditional classification once thorough studies are conducted."

Comments from Nores: "NO. Aunque los fundamentos dados por Stiles son bastantes convincentes, pienso que todavía no hay datos concluyentes como para eliminar la especie. De acuerdo al análisis de De Las Casas, que insulata es indistinguible de telasco y muy diferente de minuta muestra que no se trataría de un híbrido, porque si no tendría que tener similitudes parecidas con ambas especies. Tampoco parece ser una subespecie, ya que el rango de insulata coincide con el de telasco. Por lo tanto, lo único que quedaría posible sería un morfo de telasco. Sin embargo, como señala Cadena el grupo de capuchinos de Sporophila ha mostrado que buenas especies no son diferentes en mtDNA (Lijtmaer et al 2004 (Mol. Philo. Evol. 33:562-579). Por lo tanto, los resultados de De Las Casas no son concluyentes. En el sudeste de Sudamérica, especialmente en la Provincia de Entre Ríos de Argentinas conviven varias especies de capuchinos con rufo en el plumaje que crean dilemas semejantes al de insulata. Se ha dicho que algunas especies pueden ser morfos, híbridos e incluso plumajes de individuos de mucha edad. Short (1975), por ejemplo, trata a ruficollis y palustris como morfos de hypoxantha, y Ridgely y Tudor (1989) considera que zelichi podría ser un híbrido entre palustris x cinammomea o un morfo de cinammomea. Sibley & Monroe (1990) sugirieron que hypochroma podría ser un morfo de cinnamomea, etc. Además, un lugareño de Entre Ríos, que tenía un buen número de capuchinos en jaulas me dijo que en ejemplares muy adultos de Sporophila palustris el banco del pecho le avanzaba por el cuello formando un collar que lo asemejaba a Sporophila zelichi. Por lo tanto, si eliminamos de la lista a insulata habría probablemente que hacer lo mismo con zelichi, palustris y ruficollis."

Comments from Pacheco: "YES. Um relutante Sim! Acho que a partir dos resultados já disponibilizados por Stiles e alunos é possível afirmar que a situação tornou-se invertida. Forçoso agora é demonstrar que insulata é um táxon."