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.”