Proposal (110) to South American Classification Committee
Treat Leptotila plumbeiceps as conspecific with L. rufaxilla
Effect on South American CL: This proposal would lump two taxa that we (and most classifications) treat as separate species into a single species.
Background: Traditional classifications (e.g., Meyer de Schauensee 1970, Sibley & Ahlquist 1990, Goodwin 1983, Baptista et al. 1997, Gibbs et al. 2001) treat mostly Middle American Leptotila plumbeiceps as a separate species from cis-Andean L. rufaxilla. The two are allopatric, and are widely regarded as sister taxa or as members of a superspecies/species complex (with L. pallida, L. wellsi, and L. jamaicensis).
New information: The AOU (1983) considered plumbeiceps conspecific with L. rufaxilla, but did not provide or cite rationale. I cannot find a previous treatment of them as conspecific, including AOU chair Eisenmann's classification of Middle American birds. The AOU (1998) continued to consider them conspecific.
Genetic data (Johnson 2004; let me know if you want a pdf) indicate that plumbeiceps and rufaxilla are not even sister taxa; bootstrap and Bayesian support for a sister relationship between plumbeiceps and cassini was strong, with rufaxilla the sister taxon to plumbeiceps + cassini.
Analysis: I am unable to find any published rationale, much less data, to support either treatment. Qualitative descriptions of voice (e.g., in Hilty & Brown 1986, Gibbs et al. 2001) are "similar but different," with no indication that plumbeiceps is any more similar to rufaxilla than it is to other Leptotila voices; without a quantitative analysis, conclusions are impossible, but my crude impression is that plumbeiceps voice does differ from rufaxilla "about as much" as species-level taxa in Leptotila (and John Arvin, familiar with both, supports treating them as separate species [pers. comm.].
As for the genetic data, although taxon-sampling is far from complete, it seems unlikely that plumbeiceps and rufaxilla could possibly be sister taxa.
Recommendation: Lacking any cogent reason for lumping them, given the narrow limits among Leptotila species-level taxa, and given the genetic data, I recommend a "NO" on this.
BAPTISTA, L. F., P. W. TRAIL, AND H. M. HORBLIT. 1997. Family Columbidae (pigeons and doves). Pp. 60-243 in "Handbook of the Birds of the World, Vol. 4. Sandgrouse to cuckoos." (J. del Hoyo et al., eds.). Lynx Edicions, Barcelona.
GIBBS, D., E. BARNES, AND J. COX. 2001. Pigeons and doves. Yale University Press, New Haven.
GOODWIN, D. 1983. Pigeons and doves of the world, 3rd ed. Cornell Univ. Press, Ithaca, New York.
JOHNSON, K. P. 2004. Deletion bias in avian introns over evolutionary timescales. Molecular Biology & Evolution 21: 599-602.
MEYER DE SCHAUENSEE, R. 1970. A guide to the birds of South America. Livingston Publishing Co., Wynnewood, Pennsylvania.
SIBLEY, C. G., AND B. L. MONROE, JR. 1990. Distribution and taxonomy of birds of the World. Yale University Press, New Haven, Connecticut.
Van Remsen, March 2004
Comments from Stiles: "NO. The AOU's decision to lump them in 1983 was essentially a knee-jerk reflex in applying the old Hellmayr-Mayr-Short concept of biogeographical species, dressed up a bit in superspecies clothes. If it looks similar and is allopatric, lump as subspecies in a biogeographical species. Most Leptotila look pretty similar, including sympatric ones, so not much use that these do also. Voices of most Leptotila also sound similar to my ear, so a good quantitative analysis of recordings would be required to evaluate this. In the absence of a thorough analysis, my feeling is to dissent from the AOU and keep them separate as the rationale for lumping was never stated clearly in the first place."
Comments from Nores: "No, pienso que Remsen tiene razón cuando señala que no existe ninguna razón convincente para unir estas dos especies. Con este criterio habría que unificar la mayoría de las especies de Leptotila."
Comments from Jaramillo: "NO. Genetic differences are compelling to leave as separate species. As Manuel mentions if we use this lump as a guide, we would end up lumping many other Leptotila."
Comments from Zimmer: "NO. Although there is little published rationale for one course or the other, I think the burden of proof is on those that would lump. From personal experience, I think the vocal differences are significant."