Proposal (103) to South American Classification Committee
Recognize Dacnis egregia as a separate species from D. lineata
Effect on South American CL: This proposal would split our Dacnis lineata into two species, with recognition of Trans-Andean egregia group as a separate species.
Background: The bird we treat as one species, Dacnis lineata (Black-faced Dacnis), has three disjunct subspecies: (1) the subspecies egregia in the Cauca and Magdalena valleys of Colombia; (2) the subspecies aequatorialis in western Ecuador, and (3) nominate lineata in most of Amazonia. This is the traditional classification (e.g., Hellmayr 1935, Meyer de Schauensee 1966, 1970, Storer 1970, Meyer de Schauensee & Phelps 1978, Hilty & Brown 1986, Isler & Isler 1987, Ridgely & Tudor 1989, Sibley & Monroe 1990).
The Amazonian population has a white belly, undertail coverts, underwing coverts, and mostly concealed white feathers at sides of breast, whereas in the other two all these areas are yellow; nominate birds are also slightly bluer, less greenish blue. The plumage patterns are extremely similar if not identical except that the egregia group evidently has more extensively contrasting areas on breast to the point that the yellow is clearly evident at the sides of the breast in the field (as illustrated in Hilty & Brown 1986, Ridgely & Greenfield 2001). Hilty & Brown (1986) indicate that egregia and aequatorialis differ in that the latter's belly was more deeply yellow and that the blue-green colorations was evidently greener. Females also differ slightly between the two groups, with nominate birds having whiter, less yellowish, bellies.
New information: Ridgely & Greenfield (2001) treated egregia group as a separate species, with the following note:
"Trans-Andean D. egregia is regarded as a species distinct from cis-Andean D. lineata (Black-faced Dacnis), based on its striking plumage differences and disjunct range."
Analysis: The only plumage difference that might be associated with a "species-level difference" is the more extensively yellow sides of the egregia group, emphasized by Ridgely & Greenfield's English name, "Yellow-tufted Dacnis." There are no qualitative vocal descriptions for comparison or any other relevant information that I could find.
By comparison in a congener, trans-Andean D. cayana baudoana differs much more from other D. cayana taxa than these subspecies of D. lineata do from one another, and are furthermore likely to be parapatric or nearly so; thus, one could build a better case for a split there than in D. lineata. Bob and others often use "disjunct" distribution as evidence for separate species status. I point out again that "disjunct" involves a continuum from separation by a few kilometers (as in river-barrier cases) to thousands of km, with no way that I can see to decide "how disjunct" two populations need to be to be considered separate species. In contrast, I would emphasize the opposite, namely that parapatry with no evidence of gene flow provides definitive evidence for species rank (as perhaps in the baudoana example above).
Recommendation: I vote "NO" on this proposal. Several other similar "splits" have at least been accompanied by qualitative vocal descriptions. This one rests completely on whether the yellow patches at the sides of the breast merit species rank; they are indeed suggestive, but it need to be convinced.
Partial Literature Cited:
HELLMAYR, C. E. 1935. Catalogue of birds of the Americas. Field Mus. Nat. Hist. Publ., Zool. Ser., vol. 13., pt. 8.
HILTY, S. L., AND W. L. BROWN. 1986. A guide to the birds of Colombia. Princeton University Press, Princeton, New Jersey.
MEYER DE SCHAUENSEE, R. 1966. The species of birds of South America and their distribution. Livingston Publishing Co., Narberth, Pennsylvania.
MEYER DE SCHAUENSEE, R. 1970. A guide to the birds of South America. Livingston Publishing Co., Wynnewood, Pennsylvania.
RIDGELY , R. S., AND P. J. GREENFIELD. 2001. The birds of Ecuador. Vol. II. Field guide. Cornell University Press, Ithaca, New York.
RIDGELY, R. S., AND G. TUDOR. 1989. The birds of South America, vol. 1. Univ. Texas Press, Austin.
SIBLEY, C. G., AND B. L. MONROE, JR. 1990. Distribution and taxonomy of birds of the World. Yale University Press, New Haven, Connecticut.
STORER, R. W. 1970. Subfamily Thraupinae. Pp. 246-408 in "Check-list of birds of the World, Vol. 13" (Paynter R. A., Jr., ed.). Museum of Comparative Zoology, Cambridge, Massachusetts.
Van Remsen, February 2004
Comments from Robbins: "NO. Clearly, more information is needed on the entire complex before any changes should be made."
Comments from Zimmer: "NO. Published evidence still too weak in my estimation."
Comments from Stiles: "NO, more real evidence required (voice, genetics, morphometrics, etc.) - when this evidence is published, we´ll see if a split is warranted."
Comments from Nores: "NO. El pattern the color tan particular y casi idéntico entre las poblaciones cis y transandinas sugieren para mi subespecie y no especies, y sería importante esperar estudios genéticos."
Comments from Jaramillo: "NO. I bet that further work will reveal that a split is fine, but until that oft mentioned "further work" is done."
Comments from Schulenberg: "NO. I don't know how one would "know", under a biological species concept, what these plumage differences represent in the case of two taxa that are allopatric. Surely some other type of evidence should be brought to bear. Striking phylogenetic species, of course.”