Proposal (494) to South American Classification Committee
Elevate Phibalura flavirostris boliviana to species rank
Effect on South American CL: This proposal split a species into two separate species.
Background: Be sure to see Hennessey (2011) for details – I can send a pdf if needed. Here is the abstract:
ABSTRACT.—The Swallow-tailed Cotinga (Phibalura flavirostris) has traditionally been considered to consist of two subspecies, P. f. flavirostris of southeastern Brazil’s foothill forest and, isolated by ,2,500 km, a population of P. f. boliviana in central-western Bolivia. The plumage of the two taxa is distinctly different; boliviana males have a longer tail, and body plumage is significantly less sexually dimorphic. The iris of boliviana is mustard yellow, distinct from the blood red iris of flavirostris. P. f. boliviana has dull to bright orange-yellow feet whereas flavirostris has pink feet. Only one vocalization type is recorded for P. f. flavirostris, whereas at least five calls and a song are known for P. f. boliviana, which vocalizes significantly more often. The Brazilian P. f. flavirostris has strong seasonal movements, whereas P. f. boliviana has no seasonal movements. Given the diagnosable differences between the two taxa, it is highly probable they are separate lineages. P. boliviana qualifies as critically endangered for its declining small population due to continual habitat loss.
New information: Very little was previously known about the biology of the highly isolated P. f. boliviana. Hennessey (2011) assembled photos of 17 different individuals, field observations of 46 individuals, and tape-recordings of 13 individuals; he also examined the 3 known specimens. Elaborating slightly on the abstract, the tail length is based on that of the only male specimen, which is >5 mm longer than the longest tail in nominate specimens examined, but differences in overall body size were not mentioned; nonetheless, field observations suggest that the tail is relatively longer. The lower degree of plumage dimorphism is based on male-like black upperwing coverts in “some” female boliviana, and the statement “some female individuals of boliviana have plumage features similar to the male, whereas the sexually dimorphic body plumage of flavirostris is clearly demarcated in all specimens (n= 5-12).” No further details were provided. However, nominate females are more extensively barred below than boliviana females, which show no barring (N=32 individuals in field). The N for iris color is 17 for boliviana, 10 for flavirostris. The N for foot color was not stated. The vocal differences are nest appreciated by inspecting the sonograms
Analysis and Recommendation: The manuscript comes across as written by a lobbyist for species rank to assist in upgrading conservation protection for boliviana. I don’t blame Hennessey for feeling that way – I would, too. It’s the WJO editor’s fault for not helping the manuscript strike a more objective tone, and for not catching gaffs such as equating geographic isolation with reproductive isolation in the context of taxon ranking (otherwise populations of every non-continuously distributed species on the planet could each be considered reproductively isolated “species”). There are no playback trials, which seems a little odd given that the author studied nominate birds in the field as well. The seasonal movements of nominate vs. the absence of any in boliviana is used to support species rank without comment; however, in many birds, seasonal movements can vary among individuals of the same population and even within a single individual in different years, much less among subspecies.
Those problems aside, I think Hennessey has assembled sufficient evidence for changing the taxon rank of boliviana and has placed the burden-of-proof on its treatment as a subspecies of P. flavirostris. Hennessey succeeds in emphasizing the plumage differences between the females by noting that none other than Frank Chapman, David Snow, and Niels Krabbe all assumed that the female of boliviana was mis-sexed and was actually a young male. In aggregate, I think that the plumage, bare parts, and vocal differences show a degree of phenotypic divergence association with species-level differences in birds, so I favor a YES on this one
HENNESSEY, A. B. 2011. Species rank of Phibalura (flavirostris) boliviana based on plumage, soft part color, vocalizations, and seasonal movements. Wilson J. Ornithology 123: 454-458.
Van Remsen, September 2011
Comments from Stiles: “YES - the evidence now available, albeit imperfect, definitely favors treating boliviana as a species, and shifts the burden of proof onto those who would lump it.”
Comments from Robbins: “I’m on the fence on this for the following reasons: I agree with Van’s comments concerning how the Hennessey paper could have been improved on a number of levels. Plumage morphological differences appear to be minimal between these two taxa, but if soft part colors described are accurate, those may be important. It is difficult to access the vocal aspects because only analogous calls are presented in the paper, none are available on xeno-canto, and only three poor-quality vocalizations (only calls) of only boliviana are available on the Macaulay Library website. I’m perplexed to why the recorded vocalizations mentioned in the paper are not *all* deposited at one of the above sites for independent evaluation. As a result, one is left with evaluating spectrograms in the paper. Comparison of “selected” calls of flavirostris (Fig. 1) to those of boliviana (Fig. 2; those appear to be analogous calls, unlike A, B, D, and E in Fig. 3; note that Fig. 1 & 2 are not on the same scale) reveals that they appear quite similar in structure, frequency and duration. The purported song of boliviana (n = 1) is striking similar in all attributes of the “selected” call notes of flavirostris (Fig. 1). As Van points out, seasonal movements and geographic disjunction have little bearing on assessing species status. In sum, given the information available, differences in plumage and vocalizations (calls) are quite minor and bring into question whether these deserve species recognition. I presume obtaining unequivocal song of both taxa and genetic data will help clarify taxonomic status.”
Comments from Pacheco: “YES. As provas disponibilizadas por Hennesey, ainda que questionáveis em certa medida, implicam no tratamento boliviana como espécie.”
Comments from Cadena: “A rather tentative NO. Clearly, the two forms of P. flavirostris are on separate evolutionary trajectories and differ in several important ways, so they would be considered separate species under most species definitions. Are they reproductively isolated entities such that we should treat them as distinct based on the Biological Species Concept? It is very hard to tell because the data, although suggestive, are not entirely conclusive. But it is hard to imagine better data than that available for these allopatrically distributed and rare forms. A difficult one... “
Comments from Stotz: “YES. I have gone back and forth on this one. I think the plumage data could go with either treatment, but I think the vocal data and analysis is sufficient to split these two taxa.”
Comments from Pérez: “NO. Even when there are clear differences between these taxa I am not quite convinced those argue strongly in favor of species status. Morphological differences are similar to those found within species and some ecological differences, such as seasonal movements, as Van indicated, could be found among species populations. Additionally, vocal differences are based on a limited amount of data and are difficult to evaluate as different types of songs or calls are compared. As Daniel pointed out, it is difficult to do this type of research in rare species; however, vocal information for this study was gathered in few days and it might be worth to do an extra effort to increase sample size and provide more conclusive data (although I understand resources for field research are not always available).”