Proposal (#370) to South American Classification Committee

 

Elevate subspecies insularis of Sporophila intermedia to species rank

 

Effect on South American CL: This proposal would split one species from within our broad Sporophila intermedia.

 

Background (taken from Restall 2002): Sporophila intermedia insularis was described by T. Gilliard in 1946 from Trinidad (and also occurs in Venezuela north of Orinoco), and was subsequently considered a synonym of S. i. intermedia by Meyer de Schauensee (1952). It has been largely ignored ever since. It was described as differing from intermedia in having white neck patches, but this character evidently appears to varying degrees within S. intermedia.

 

New information: Restall (2002) first noticed that insularis also differs from all other intermedia populations in having a white bar across the rump, but his initial hypothesis was that this just represented individual variation within intermedia. After studying about 100 male specimens of intermedia and about 35 of insularis (determined as such by the white rump bar?), Restall found the following differences:

 

1. significantly larger bill
2. significantly larger body weight
3. significantly longer tarsus
4. qualitative differences in songs based on aviary birds

 

He also noted that the one known nest of insularis differed in color from those of intermedia (N=?). Restall also noted some other potential differences (e.g., vocal mimicry) that need to be investigated.

 

The most important point, however, is that insularis and intermedia are broadly sympatric, from Trinidad across northern Venezuela. One could attribute this to some sort of polymorphism or age difference in male plumage of the eastern populations of intermedia; however, that specimens identified as insularis by rump pattern also have statistically bigger bills and longer tarsi would be unusual for a plumage variant.

 

Analysis: South American Sporophila represent a drastically understudied group in terms of male plumage variation (notorious in this genus) and species limits. In the case above, ideally we would have breeding season data that show that both forms breed sympatrically with the vocal differences described by Restall quantified in detail, as well as genetic data. What we have is a study that should provoke such an investigation. But is what we have sufficient for elevating insularis to species rank and placing burden-of-proof on the idea that insularis represents only within-species plumage variation? My main concern is the possibility of seasonal movements (well known in other species in this genus) creating sympatry only outside the breeding season.

 

Recommendation: I recommend, tentatively, a YES on this one for two reasons: (1) the morphological characters indicate to me that this is more than just a plumage variant, and (2) Restall's extensive experience with Sporophila and other small seed-eating birds, including from an avicultural perspective, leads me to suspect strongly that he's got it right.

 

English name: Restall recommended "Ring-necked Seedeater" for insularis in recognition of a plumage difference between it and Gray Seedeater, and in recognition of the local name "Ring-neck" in Trinidad. I would have gone for "Band-rumped Seedeater" myself to emphasize the overlooked but diagnostic character, and because the white in the neck doesn't really form a ring. Discussion?

 

Lit Cit:

MEYER DE SCHAUENSEE, R. 1952. A review of the genus Sporophila. Proc. Academy Natural Sciences Philadelphia 104: 153-196.

RESTALL, R. l. 2002. Is the Ring-necked Seedeater (Sporophila insularis) from Trinidad extinct, or is it a cryptic species widespread in Venezuela? Pp. 37-44 in "Studies in Trinidad and Tobago ornithology honouring Richard ffrench" (Hayes, F. E., and S. A. Temple, eds.). Occasional Paper No. 11, Department of Life Sciences, University of West Indies, Trinidad.

 

Van Remsen, September 2008

 

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Additional comments from Steve Hilty and Robin Restall (an exchange between them):

Hilty to Restall:
"I read, recently, your article on Sporophila insularis. You make an interesting case in support of Sporophila insularis; however, I am not sure I am fully convinced. The measurement differences were ever so slight (even if they did apparently show statistical significant) and what you have shown looks a bit like some of the Grant's work (popularized in "Beak of the Finch") with Galapagos finches, albeit on a tiny scale, with these measurement averages of theirs shifting a bit from decade to decade with environmental changes on islands. Am left wondering what these tiny measurement differences mean."

 

Restall response to Hilty:
"One of the ornithologists at UCV here did her PhD thesis in Kansas and worked at a distance with Jorge Perez. At one point in time, they took tissue from a good sample of insularis and one of intermedia. There was a distance between the two, although admittedly they were close. The same study showed that schistacea was the same distance from intermedia/insularis as was Oryzoborus angolensis."

 

Further thoughts from Hilty:

"First: Sporophila is notable for polymorphism in plumages.

"Second: Regarding S. insularis, little is known about seasonal movements, breeding overlap, or interspecific territoriality (assuming they are valid species) with allied S. intermedia. Nor is their much information on habitat usage (I have none)? The question of how the two taxa might achieve reproductive isolation remains puzzling?

 

"Third: Vocal data might be helpful. Most males of S. intermedia seem to mimic, in the wild. It could be helpful to determine if S. insularis also is or is not a mimic, or if its songs are different than those of S. intermedia.

 

"[Restall tells me that he does have song cuts of S. insularis and will have them digitized for further analysis so this could be useful]

 

"To follow up on Restall's comments, perhaps some additional genetic work would be helpful. I suppose my conclusion is that Restall just might be on to something interesting here, but perhaps a proposal to validate or refute S. insularis as a valid taxon is premature at this point. Could be worthwhile letting the story unfold."

 

Comments from Cadena: "NO. I am afraid all the necessary data are not quite there yet. The data do seem suggestive (particularly the fact that birds with a particular plumage phenotype are also different in morphometrics), but I would like to see a detailed study that allows rejecting the possibility of seasonal movements that Van mentioned. Also, note that the differences in means of morphological measurements between insularis and intermedia need not imply diagnosability, as there is some overlap in at least some of them; because sample sizes are rather large, I am actually not very impressed to see that t-tests find significant differences between insularis and intermedia. All this, in addition to Hilty's comments, suggests it would be best to wait for more detailed analyses to unfold."

 

Comments from Nores: "NO. Aunque Restall puede tener razón, los elementos aportados no son del todo convincente y hay un poco de razonamiento circular. Aunque él menciona que la banda blanca de la rabadilla está presente en todos los ejemplares de insularis (por él atribuidos), no significa que algunos de ellos no sean intermedia. Además, las medidas en que él basa la separación de los ejemplares con banda blanca no son tan diferentes y hay bastante superposición. Las medidas del pico difieren en alrededor de 0.5 mm y la medida del tarso, aunque alcanza a 1 mm, es siempre más relativa. En síntesis: el considera que todos los ejemplares con banda blanca en la rabadilla son insularis porque son más grandes, lo que en la realidad no es así. El promedio es mínimamente más grande, pero no los ejemplares en particular. Si todos los individuos con banda blanca en la rabadilla fueran más grandes, si habría que admitir que son dos especies diferentes. Como el análisis molecular de un ejemplar sugiere que puede ser distinta, yo esperaría a tener otros ejemplares para hacer el análisis, antes de elevarla a especie."

 

Comments from Zimmer: "NO, for reasons stated by Daniel and Steve."

 

Comments from Robbins: "NO, for the time being. The relatively minor morphological differences coupled with the uncertainty about breeding sympatry and quantified song differences beg for further study before making a taxonomic change."

 

Comments from Stiles: "NO, for the moment. Robin may well be right, but I feel that more data, especially from the field and genetics, are required. Variation in plumage of the magnitude of that described by Robin occurs in related species and notably, in the bogotensis race of intermedia itself (see Stiles 1996, Ornitología Neotropical); because song is learned in these birds, its use in taxonomy, while not to be ignored, should be done with great care; and while mean differences in several dimensions exist, overlap is also great such that many individuals will not be distinguishable by this means. I find it odd that the distributions of two species so similar could overlap so widely without any indication of ecological separation. Especially for such cryptic species, detailed genetic and vocal data have proven critical in confirming their distinctness and it seems prudent to wait for such data here before going ahead with this split."

 

Comments from Stotz: “NO.  There is some evidence to support this change, but like others I am concerned by possibilities of seasonal movements inflating observed sympatry and the relative weakness of both morphological and ecological differences.”

 

Comments from Jaramillo:  YES. This does indeed seem similar to Darwin’s Finches as Hilty mentions, and that is precisely why I buy the argument. Differences in plumage and morphology in sympatric populations of seed-eating finches suggests to me that we are not talking about morphs, hybrids or anything other than two very similar but different populations. It seems like Sporophila are the Neotropical version of northern hemisphere Larus – lots of grey areas and a very quick and massive radiation that went on. Some may still be working themselves out (capuchinos), while others are polymorphic, and others are over-lumped etc. I think that Restall’s logic is sound here, it would be nice to have more data, but what is there seems fine to me.”

 

Comments from Pacheco: "NO.  Ainda que concorde que há alguma possibilidade de acerto neste tratamento, as evidźncias presentes sčo especulativas e nčo foram devidamente imunizadas.