Proposal (#64) to
Treat Myioborus castaneocapillus as a separate species from M. brunniceps
Effect on South American CL: This proposal would split our Myioborus brunniceps into two species, with recognition of northern castaneocapillus* as a separate species.
Background: The bird we treat as one species, Myioborus brunniceps (Brown-capped Redstart), has a disjunct distribution, with one subspecies group in the Tepui region of Venezuela and the other in the Andes from central Bolivia to central Argentina and the mountains of Córdoba. This follows the traditional classification (e.g., Hellmayr 1935, Meyer de Schauensee 1966, 1970, Lowery & Monroe 1968, Meyer de Schauensee & Phelps 1978).
The subspecies castaneocapillus is very similar in plumage to brunniceps, differing primarily in amount of white in face, but the subspecies duidae at least superficially looks more similar to M. cardonai of Cerro Guaiquinima than it does to castaneocapillus.
New information: Ridgely & Tudor (1989) considered the three northern subspecies as a separate species, M. castaneocapillus (with duidae and macguirei) from M. brunniceps. This was based in part on the highly disjunct distribution, but also on differences in the song. They described that of the castaneocapillus group (subspecies not specified) as "a thin unmusical chipper, starting slowly, gradually speeding up and descending in pitch," whereas that of brunniceps was described as "an even, fast, thin, sibilant trill with slight crescendo effect." Curson et al. (1994), Sibley & Monroe (1990), and Hilty (2003) all followed this and elevated castaneocapillus to species rank. Hilty (2003) gave a similar description of the song of subspecies castaneocapillus that is similar to that given in Ridgely-Tudor, but also added "Less often gives rather slow, warbling trill, colorless and more like others of genus"; the songs of M. cardonai and M. albifacies evidently remain unknown.
Analysis: Based on geography, I predict that the castaneocapillus group is genetically closer to the allotaxa cardonai and albifacies, both traditionally ranked as species, than to distant brunniceps; and this will provide yet another example of an emerging pattern, namely "breakout species" that are phenotypically different from any population of a widespread species but genetically closer to nearest population of the widespread species than populations within that widespread species are to one another. Ridgely & Tudor (1989) suspected that cardonai and albifacies were best treated as conspecific, pointing out that their main differences, in crown and face color, are plastic characters within other Myioborus taxa treated as conspecific, e.g., M. melanocephalus. These taxa all appear to form a superspecies (and Sibley & Monroe also include M. pariae in this superspecies).
Recommendation: I reluctantly vote "NO" on this proposal. Predictions and instincts are not sufficient for making decisions. This is another example of what is almost certainly a "correct" taxonomic decision based on substandard published data (e.g., Hyloctistes proposal). Although I bet that Bob and Steve Hilty have it "right," I do not think that the published data are sufficiently strong for a change from historical status quo. To make official changes, I hope that we require more rigorous evidence than a couple of qualitative descriptions of songs (of notoriously variable parulids no less). South American Myioborus represent a complex taxonomic situation that, in my opinion, needs a thorough overall study, before we make isolated changes; even so, I could be persuaded to do a piecemeal change if a short paper with sufficient Ns of sonagrams were published.
* Correct spelling is castaneocapillus, not castaneocapilla (David & Gosselin 2002a).
CURSON, J., D. QUINN, AND D. BEADLE. 1994. Warblers of the Americas. Houghton Mifflin.
HELLMAYR, C. E. 1935. Catalogue of birds of the Americas. Field Mus. Nat. Hist. Publ., Zool. Ser., vol. 13., pt. 8.
HILTY, S. L. 2003. Birds of Venezuela. Princeton University Press, Princeton, New Jersey.
LOWERY, G. H., JR., AND B. L. MONROE, JR. 1968. Family Parulidae. Pp. 3-93 in "Check-list of birds of the World, Vol. 14" (Paynter R. A., Jr., ed.). Museum of Comparative Zoology, Cambridge, Massachusetts.
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.
Comments from Stotz: "YES. I recognize that this is not the best-established split, but it is hard to imagine that castaneocapillus has anything to do with brunneiceps. Perhaps more to the point, the basis for any treatment of Myioborus is very weak. It is purely historical accident that we consider brunneiceps and castaneocapillus conspecific while pariae is a distinct species. Peters (Vol. 14) refers you to the Phelps' Venezuelan list for reasons for treating pariae (described as a subspecies of brunneiceps) as a distinct species. All that the Phelps' say is "Por los disenos distintivos de la cabeza de la cola creemos que debe ser considerada como una especie." I would suggest that Ridgley and Tudor's vocal descriptions combined with the fact that brunneiceps is at the southern end of the Andean chain, while castaneocapillus is a Tepui endemic with ties to montane forms in Venezuela (that we treat as separate species) is a stronger argument for status as a separate species than stronger yellow rather than white facial markings and more white in the tail (characters for pariae)."
Comments from Robbins: "[YES] I have field experience with only castaneocapillus (from Roraima), but I do agree with both Ridgely and Hilty's description of the song of castaneocapillus. I have no doubt that Bob accurately described the song of brunniceps. Finally, from a biogeographical standpoint the split makes sense. Hence, I vote "yes".
Comments from Schulenberg: "My vote is YES.
Jorge Perez (now, I believe, back in his native Venezuela) did a great study of Myioborus (Molecular systematics, biogeography, and population history of the genus Myioborus [Aves, Parulinae]) for his doctoral thesis (2002, University of Missouri-Saint Louis).
Jorge had excellent taxon sampling (21, I think, taxa of Myioborus) and utilized three mitochondrial genes (cytochrome b, ND2, ND3), with a little over 2500 base pairs combined. His trees are well resolved. Based on Jorge's results, brunniceps is basal to a widespread clade of upper montane Myioborus; castaneocapillus is nested well within the clade, and is separated from brunniceps by several other taxa. Clearly these are different species, as would be expected by geography and is consistent with the other, more limited information.
Normally of course I hold firm for a "publication" as the basis for our revisions to the base list. Jorge may have a paper on his results already submitted or in press, I don't know. But the research has been done, it has been written up (at least in thesis form), and it seems silly to me to pretend that it does not exist. Jorge has given at least one talk at an American Ornithologists' Union (perhaps at more than one meeting), he's given invited seminars on his research, and so his work is becoming known. His thesis is something that we can cite (if he doesn't have something in press already), and enterprising types can track down a copy. Of course, if he publishes his phylogeny, then that would not be necessary. In the meantime, there is a copy of his thesis at Field Museum, and if necessary I can send copies of some or all of it to anyone on SACC who is interested. Chapter headings are Moleculuar phylogenetics and biogeography of the genus Myioborus (Aves, Parulinae); Biogeographic patterns in the Pantepui region: inferences from mtDNA phylogeography of Myioborus castaneocapillus (Aves: Parulinae); and Patterns of avian geographic differentiation in Neotropical montane habitats: a mitochondrial DNA phylogeographic study of the Myioborus miniatus (Aves, Parulinae) complex."
Comments from Jaramillo: "YES. I have a lot of experience with brunniceps and was astounded to see how different castaneocapillus looked and acted in the field when I saw this taxon. For one castaneocapillus looked darker and grayer to me, and I recall that it looked large (not sure if measurements bear out this difference). However, I do recall hearing some songs, which were quite different from the very high-pitched, even trill (can recall Blackpoll) of brunniceps. These field impressions are just that impressions but they certainly move my gut to the split side on this issue, add to this the data that Tom mentions exist and I am perfectly comfortable accepting this change. Theses are stored and archived, while not peer-reviewed publications they are available and we can cite the specific thesis in this case."
Comments from Zimmer: "I vote "YES". Besides the range disjunction and vocal differences, the Jorge Pérez thesis does give us something to hang this change on, even if it isn't published in the traditional sense."
Comments from Nores: "YES. Yo solo tengo experiencia con brunniceps, pero parece evidente que, por distribución geográfica, coloración, canto y sobre todo genética (de acuerdo a los datos de Jorge Pérez mencionados por Schulenberg), son especies diferentes."