Elevate Phibalura flavirostris boliviana to species rank

 

Proposal (494) to South American Classification Committee

 

 

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

 

Literature Cited

 

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

 

 

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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: “NO.  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).”

 

Comments from Jaramillo: “YES.  I can see why some have issues with this proposal because datasets are not huge, either vocal or morphological, and the question of reproductive isolation is not tested directly. However, the species is rare, and I see this as an honest effort to document various aspects of the biology of this taxon, and to publish them for evaluation. It would be great if there was more information right now, but as noted, this is difficult for a rare species in an area that is actually somewhat difficult to get to. I can also see why there is a concern that this paper is lobbying for a certain position that may in the end help this endangered taxon. But let’s hold on a moment and step back and ask a question. Aren’t all papers essentially lobbying for a point of view, an opinion? These may not have immediate political or research funding consequences, and they may be written in more objective language perhaps, but I certainly always read a taxonomic paper as if it was lobbying a position. The question is whether the data supports the position, and also if it conforms to my way of seeing the world, which may differ subtly from that of others. So yes, I see the lobbying portion here, but don’t see it as very different from many other taxonomic papers. On the other hand, I think that it is highly positive that at least this group in Bolivia is actively gathering data of biological significance on these rare birds, and doing the work of publishing in legitimate journals. This is a very good thing! That doesn’t mean one has to accept the position of the paper of course, but this is certainly a huge improvement over the “field guide taxonomy” issues that some of us have been concerned about (or even involved in!).

               “Having said that, I think the scale is tipped to separating these two as species, and in reading between the lines assessing what we know about these taxa in the context of other suboscines. The voice data is interesting in a non-standard way. We do not have 30-40 territorial vocalizations from two similar looking taxa here that sound obviously different. But one issue that is not highlighted properly in the paper is the differences in vocal behavior. The poorly known and rarely seen (remember there are but a handful of specimens of this thing) boliviana is shown to have a wider vocal repertoire than flavirostris. This is odd!! You would think that the vocal info we have from years of people annually seeing flavirostris would be much greater and more diverse but it is not. The reality is that flavirostris is a very quiet species, vocalizing very little and essentially only one vocal type is known. I think that given the substantial difference in field time biologists have had with each of these taxa, the fact that boliviana vocalizes readily, and has a diverse set of vocalizations is likely biologically significant. These two taxa are not acting like the same thing, and particularly in their vocal behavior, which we know is generally taxonomically important in suboscines. Then we add various other data: 1) differences in sexual dimorphism 2) differences (although not yet quantified with adequate sample of specimens) in male tail length – likely a sexually selected trait 3) soft part color differences 4) habitat differences 5) differences in residency/migration. All of this adds up for me, perhaps looking at it more from a behavioral ecology perspective, which in the end was the field I came out of, that we have two radically different creatures here. In time, as we find out more, we will likely see that the mating strategies will likely differ between these two; and differences in ecology are certainly reinforcing the split in these lineages. We have differences in various traits that are almost certainly proxies to pair formation – voice, plumage, and soft parts. This is enough to satisfy me that we have two species. I am writing in more detail here than I usually do, as I do think the argument is strong enough to separate these two, and I realize that the conservation level immediately pops for boliviana if it is considered a species. It is not that this decision is any more important than any other we make, but I wanted to try and be clear about my opinion of the data and try and be as clear as I can about it. I should add that I have yet to see either of these taxa in the field, so I am working off the written, rather than any personal experience I have with these birds.”

 

Comments from Zimmer: “YES”.  The supporting evidence seems a bit weak, both as regards sample sizes and the interpretation of the morphological and vocal differences.  In reading the paper, I found myself confused over the number of specimens of nominate flavirostris that were actually examined [Plumage comparisons were stated in the Methods section to be based on “eight specimens”, yet later, the mean of male flavirostris tail lengths was given as based on an n of 23 specimens, and, still later, the statement is made that the “sexually dimorphic body plumage of flavirostris is clearly demarcated in all specimens (n = 12)”!].  Nonetheless, I do find the described differences in iris color and leg/feet color between the two taxa compelling.  Hennessey (2011) states that iris color is consistently blood red for flavirostris and mustard yellow for boliviana, and that there is no known overlap.  He goes on to state that leg/foot color (pink in flavirostris, orange-yellow in boliviana) is equally consistent and non-overlapping.  My field experience with this complex is extensive for flavirostris and non-existent for boliviana, but the soft part colors as described by Hennessey for flavirostris are absolutely consistent with my field experience.  Furthermore, a perusal of photographs (mine and those of numerous photographers as displayed on the website WikiAves) of dozens of male and female flavirostris failed to find any exceptions to the described colors.  Also, the described differences in barring patterns on the underparts of female flavirostris versus those of boliviana are consistent with my field experience, and with photographs and specimens that I have examined of flavirostris.  I am less impressed by the observed difference in male tail length, given that there is only 1 male specimen of boliviana, but it is worth reiterating that the single specimen of boliviana fell outside the range of 23 specimens of flavirostris with respect to tail length.  From looking at the spectrograms, I’m inclined to think that the extent of the vocal differences may be overstated – the tracings of those calls don’t look that different to my eye.  But, I agree with Alvaro that there do appear to be real differences in the vocal behavior as regards frequency of calling.  I have never found flavirostris to be particularly vocal, and certainly have never witnessed anything close to the “80 calls/minute for four minutes” described for boliviana.  In sum, I think these taxa are on independent evolutionary trajectories, and the demonstrated differences in soft part colors, female plumage and male tail length, along with differences in vocal behavior, are enough to warrant species recognition for boliviana, even though I’m sure we would all like to see more robust sample sizes and analyses.”

 

Comments from Nores: “NO. Although I value greatly the contribution made by Hennessey on this near-unknown bird, the morphological and behavioral differences that exist between the two forms, are to me to subspecies level (megasubspecies on the concept of Amadon and Short. 1976. Treatment of subspecies approaching species status. Syst. Zool. 25:161-167).”