Proposal (204) to South American Classification Committee

 

Treat Polioptila facilis and Polioptila paraensis as a separate species from P. guianensis

 

Effect on South American CL: This proposal would add two newly split species to the list.

 

Background: Whitney & Alvarez-Alonso (2005) in their paper describing a new gnatcatcher they also present evidence to split the current "Polioptila guianensis" into 3 species. Their conclusion that this taxon represents three separate species is based on vocal & morphological evidence along with their allopatric ranges.

 

The authors also have stated that some other species complexes in this genus that comprise of sister taxa show lower levels of phenotypic differentiation both vocally and morphologically. Where as members of the "Polioptila guianensis" complex show roughly equal phenotypic differentiation. Thus treatment as a full species seems warranted.

 

Recommendation: Based on the vocal, morphological, and distributional information. Along with currently recognized species limits in this genus, I believe this paper clearly document both as full species-level taxa. I recommend a "yes" vote to add these newly split gnatcatchers to the South American list. As common names, Rio Negro Gnatcatcher for P. facilis and Para Gnatcatcher for P. paraensis as suggested by the authors seem fine.

 

References:

 

Whitney, B.M., & Alvarez-Alonso, J. 2005. A New Species Of Gnatcatcher From White-Sand Forests Of Northern Amazonian Peru With Revision Of The Polioptila guianensis Complex. The Wilson Bulletin 117(2): 113-127.

 

Daniel Zimberlin, February 2006

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Comments from Stotz: "YES. Seems clear that if clementsi is recognized as a species, we should treat each of these taxa as separate species. Vocal differences are consistent with geography, and given the subtle differences that seem to matter in gnatcatchers, this treatment seems consistent with other species in the genus."

 

Comments from Zimmer: "NO. I'm really on the fence with this one. The three taxa (guianensis, facilis, paraensis) appear to show diagnostic differences in tail pattern and loudsong, and may differ in iris color. However, I'm not really blown away by the degree of vocal differentiation (either in looking at the spectrograms or through my own field experience with each of the forms), especially when you take into consideration that we're talking about oscine (rather than suboscine) passerines. The authors address this point, and I agree wholeheartedly with their statement that: "The potential to learn some elements of song does not exclude the possibility, or even the probability, that vocal templates of oscines are a phenotypic expression of genetic determination and are thus potentially informative in taxonomic and systematic study." This having been said, I would like to see a larger sample size and geographic spread of recordings for each taxon, to look for possible within-taxon geographic structure to vocal characters. If I am reading it correctly, the sample sizes for loudsongs (number of individuals) are guianensis = 2 (from 1 locality), facilis = 7 (from opposite sides of the upper R. Negro at Sčo Gabriel da Cachoeira), paraensis = 12 (from 7 localities). I would consider paraensis to be fairly well represented, but the samples of the other two are decidedly limited in scope. When you look at the extent of geographic differences in vocalizations of Tropical Gnatcatcher (P. plumbea) and Masked Gnatcatcher (P. dumicola), which seemingly sound drastically different every time you move a few hundred km, it's hard not to feel a little ambivalent when looking at the relatively minor differences seen in the spectrograms of the various guianensis taxa, especially when you realize the small and geographically restricted sample sizes involved. And, although this hardly constitutes proof or even a meaningful example of structured playback experiments, Andrew Whittaker tells me that he has had guianensis at Manaus respond to tape playback of paraensis.

 

“The question in my mind is how the noted vocal and morphological differences within the guianensis complex stack up relative to differences between taxa already treated as species within the genus. Again, it's a mixed bag. Potential iris-color differences could be significant if confirmed to correspond to named taxa. Plumage differences (mainly in tail pattern) are relatively minor, although consistent with between-species differences in other species-pairs in the genus. I would argue that vocal characters are less different than the yardsticks offered by other species-pairs, and are, in my experience, much less than the aforementioned differences within plumbea and dumicola. This may be less of an indictment of splitting guianensis than it is an argument for splitting within plumbea and dumicola, but it still relates to the question of appropriate yardsticks of differentiation according to current taxonomy. I would also take issue with the authors' statement: "Considering the fact that another well-studied pair of sister taxa in the genus, P. melanura (Black-tailed Gnatcatcher) and P. californica (California Gnatcatcher) are not as well differentiated phenotypically in either morphologies or vocalizations (emphasis mine) as P. clementsi and P. guianensis, we are satisfied that species status is appropriate for both P. clementsi and for other taxa currently recognized as subspecies." I would consider melanura and californica to be at least as differentiated morphologically, and more differentiated vocally than the three members of the guianensis group.

 

“In sum, the authors may be right-on in treating guianensis, facilis and paraensis as separate species, and recognition of the slightly more distinct clementsi as a species (which I support) would certainly argue for that treatment. There are apparent vocal and morphological discontinuities between the taxa that correspond with the types of characters that distinguish other species-pairs in the genus. However, I'm still bothered by the small sample sizes and the lack of breadth of geographic sampling. Again, this would be less troublesome (at least in my mind) if we were talking about a suboscine genus with no pattern of within-taxon geographic variation in voice. And, I'm even more bothered by the relatively minor differences in loudsong characters relative to major differences in loudsongs between populations in the plumbea and dumicola complexes. To me, this is less about the authors being wrong in their conclusions (which I am not at all sure is the case) than it is about whether or not they have adequately made their case. I reluctantly vote NO."

 

Comments from Stiles: "NO (tentatively). Kevin's comments plus my experience with several populations of P. plumbea make me uneasy: I agree that recordings of vocalizations from more of the ranges of the putative species would be highly desirable. It may well be that more than one species is lurking under this name (and I gather that the same could apply to P. dumicola), such that a more comprehensive review of the genus should be undertaken. The case is very like that of Momotus momota vs. aequatorialis: we voted that one down not because (most of us) really doubted that the latter was a species, but because the entire group needed a thorough review - in effect, to assure uniform treatment throughout. In the present case, it may well be that a number of gnatcatcher taxa require review and possibly splitting at least as much as guianensis, hence perhaps best to hold off on this one for now - especially as song in oscines can be quite plastic. A review of, say, vocalizations, genetics and phenotype in P. plumbea might provide an excellent yardstick for treatment of the guianensis group."

 

Comments from Robbins: "NO (tentatively). As I think everyone with broad field experience in Latin America appreciates, the current taxonomy of Polioptila is a mess with a number of species level taxa currently treated as subspecies. Thus, it should come as no surprise that an unpublished genetic data set generated by John Klicka indicates that morphology and geography can be quite misleading in delineating Polioptila species limits. For example, the presence or absence of a loral stripe in the albiloris and plumbea complexes (as it is currently constructed) is highly plastic. Hence, I don't put much weight in plumage differences between purported Polioptila species. My experience in the field and in the hand with guianensis is limited solely to the nominate form, so I can't offer any insight on the group. However, based on Kevin's remarks about his experience with these taxa and what he relates about Andy Whittaker's observing guianensis responding to tape playback of paraensis makes me pause about accepting this proposal. So, for now I vote "no", but I certainly would change my vote if additional data indicate otherwise."

 

Comments from Silva: "NO. In this case, we have only two options. The first option is to treat all four taxa as a single biological species (we are using biological species in SACC, do not we?) because the plumage differences among them are not well marked and as Kevin's has emphasized the vocal differences need to be evaluated with a much larger sample than the ones that the authors has presented. The second option is to admit that the morphological differences are enough to diagnose these four taxa and regard them as distinctive species. Because we are using biological rather than the phylogenetic species, I think we should decide to No until a more complete analysis of the vocal and genetic differentiation within this putative monophyletic group is published."

 

Comments from Pacheco: "YES. Ainda que respeitando as relevantes colocaćões de Zimmer, sou favorável ao tratamento ao nível de espécie dos trźs táxons: guianensis, facilis e paraensis sobretudo por coerźncia em reconhecer P. clementsi como espécie válida. Em minha experiźncia, Polioptila paraensis do sudoeste do Pará (veja localidade em Pacheco & Olmos 2005. Birds of a Latitudinal Transect in the Tapajós-Xingu Interfluvium, eastern Brazilian Amazonia. Ararajuba, 12(2):29-46) nčo esboćaram reaćčo a vozes previamente obtidas no Suriname ou Amapá (forma nominada)."

 

Comments from Nores: "NO. Coincido plenamente con Zimmer que las diferencias en plumaje y en canto no son suficientes para considerarlas especies. La distribución alopátrica de las cuatro poblaciones de esta especie, apoyan también la idea que se trata de subespecies."

 

Comments from Jaramillo: "YES- I find the arguments in the publication compelling. However, I do understand the point about sample sizes, and the need to expand to a wider set of taxa in Polioptila to really understand what is going on. I do think that this is what is needed, a full and complete analysis of Polioptila based on molecular, vocal and morphological features, but I don't see this in the horizon anytime soon. As such, I am left to decide on this particular proposal and this particular paper. There are some borderline issues with the completeness of the vocal dataset, but this is almost always the case in these situations. The authors likely heard many more that they did not record, and have a good feel for variation, so I am giving the benefit of the doubt somewhat on this point. But the basic point is that I read this paper, and I find myself convinced, so feel comfortable in voting for this change. With respect to the point brought up about responding to playback, to me positive responses to playback mean little. I probably could get a House Wren in Toronto to respond to a song of one from Argentina, to give an example. The real useful data from playbacks is when you have no response, it is not a symmetrical situation how you interpret positive versus no response in playback. There are many reasons why a certain bird may approach songs of non-conspecifics, or birds from distant and entirely allopatric populations. I conducted some playback experiments in the lab with Conocephalus crickets at one time, interestingly some females were drawn to white noise. They were apparently "carving out" the frequencies of interest out of the white noise! But interestingly, when a sympatric conspecific song was played it was ignored. This is an extreme situation on an entirely different group of animals, but some elements of this apply to birds."