Proposal (634) to South American Classification Committee

 

Recognize Tityra leucura as a valid species

 

 

Effect on SACC:  If adopted, this proposal would give formal recognition to “Tityra leucura”, described as a distinct species, but one that subsequently fell into obscurity and that has not been treated as a valid taxon at any level by modern authors.  As such, it would add a species to our list, and would address an issue raised in one of our footnotes regarding the relationship (if any) of leucura to a species already on our list, T. inquisitor.

 

Background:  Tityra leucura (White-tailed Tityra) was described by Pelzeln (1868) from a single specimen collected roughly 120 km southwest of Porto Velho, Rondônia, Brazil, by J. Natterer in 1829.  Subsequent authors, beginning with Hellmayr (1910, 1929) have either doubted the validity of T. leucura, or ignored it altogether, with the result that the species is absent from virtually all checklists of South American birds, including our SACC base list.  The holotype has been variously postulated to represent an atypical immature plumage of Tityra inquisitor (Black-crowned Tityra), a hybrid between T. inquisitor and some other species, an intergrade between two known subspecies of T. inquisitor (T. i. pelzelni and T. i. albitorques), or, an aberrant individual of T. inquisitor lacking pigment in the tail.

 

Whittaker (2008) summarized the history of T. leucura, compared the holotype to a series of specimens of T. inquisitor pelzelni and T. i. albitorques, and detailed field observations that he made in 2006 along the rio Roosevelt (Amazonas, Brazil), of an adult male tityra that he believed to be T. leucura.  The holotype of T. leucura differs most obviously from all other tityras in having an entirely white tail (T. cayana has an entirely black tail, and all subspecies of T. inquisitor and T. semifasciata have broad black subterminal bands that account for much of the visible tail on perched birds).  It is most similar to Black-crowned Tityra in lacking any red facial skin (as is found in T. cayana and T. semifasciata).  The holotype of T. leucura differs further from T. inquisitor in having a markedly smaller bill (length = 14.6 mm in the holotype of T. leucura, versus bill lengths ranging from 20.4–21.5 mm in 3 specimens of T. i. pelzelni and 1 specimen of T. i. albitorques as presented by Whittaker 2008) with less of a hooked tip, and the bill is bicolored: “dark reddish-brown on the maxilla and pale amber, mottled darker brown along the edges on the mandible” (versus bill entirely black in T. inquisitor).  The black crown of T. leucura extends only to just below the eye, leaving the cheeks/ear coverts white.  In this respect, it is similar to T. i. albitorques, the subspecies of Black-crowned Tityra that occurs in western Amazonian Brazil (west of the rio Madeira and rio Negro), but very different from the plumage of T. i. pelzelni, the subspecies that occurs east of the rio Madeira on the south bank of the Amazon (east to Maranhão), and of nominate T. i. inquisitor, the subspecies found throughout eastern Brazil, both of which have extensive black crowns that include the ear coverts and upper cheeks.

 

The bird that Whittaker observed was an adult tityra whose plumage was similar to that of a male Black-crowned Tityra (T. inquisitor), except that the tail was entirely white, and the black crown extended only to just below the eye, leaving the ear coverts white.  Whittaker also noted a smaller than typical bill, that imparted a “jizz more reminiscent of a Pachyramphus becard.”  Whittaker further implied that the bill was bicolored, although he seemingly erred in using the term “maxilla” when I believe he meant “mandible” in describing the bill as “dark above with a distinctly paler maxilla.”

 

Hellmayr (1910, 1929) was the first to cast doubt on the validity of T. leucura.  He identified the holotype as a “male molting from the juvenile into the first annual plumage” and further noted: “The bill, too, appears to have been retarded in its development.  It is only one-third the size of the allied species and, instead of black, dark horn brown, paler below.”  Hellmayr also regarded the absence of black in the tail with suspicion:  “The coloration of the tail gives an abnormal impression, and may be due to the absence of melanin in the pigment cells during the process of growth.”

 

Ridgely & Tudor (1994) also considered T. leucura to be a dubious species “given the lack of field records and that geographic variation in the tail color of T. inquisitor exists.”  Fitzpatrick (2004) considered the holotype to represent an abnormal subadult male, “intermediate between T. i. albitorques and T. i. pelzelni, whose ranges apparently overlap in the area where the holotype was collected.”

 

Analysis:  That the holotype was a subadult could taint the apparent significance of the distinctly smaller and differently colored bill.  However, the holotype was molting into its first basic plumage at the time of its collection, and had a mostly black crown, with only scattered remnant (from the juvenal plumage) brown feathers in the hindcrown.  So, it’s not as if we are talking about a recently fledged juvenile with a stubby, incompletely formed bill.  Also, Whittaker’s field impression of an adult bird was that it had a small bill, giving the bird a becard-like look.  I have not personally examined the holotype of T. leucura, but I have examined and photographed a number of specimens of T. inquisitor of different subspecies, and I have yet to find one that had anything other than an entirely black bill (this true even of relatively old specimens).

 

Concerning the objections raised by Ridgely & Tudor (1994):  1) Whittaker’s 2006 observation of an adult bird essentially matching the critical phenotypic characters of the holotype of T. leucura directly addresses the “lack of field records” issue; and 2) although there is geographic variation in the tail pattern (not “color”) of T. inquisitor, that variation involves only the width of the black subterminal band, not its presence or absence. 

 

Fitzpatrick’s (2004) analysis also seems flawed to me on a couple of counts.  First, I do not see how the holotype of T. leucura could be perceived as intermediate between T. i. albitorques and T. i. pelzelni.  Both subspecies have a very broad, black subterminal band to the tail, so the essentially all-white-and-pale gray tail of T. leucura is not only not intermediate in nature, but also is completely outside the spectrum of tail pattern in either T. i. pelzelni or T. i. albitorques.  Similarly, those two subspecies have identically sized, entirely black bills; so, again, the oddity of those features in T. leucura can’t be explained as “intermediate”.  The most obvious character in which T. i. pelzelni and T. i. albitorques differ is in the extent of the black crown.  In this character, the holotype of T. leucura more resembles T. i. albitorques, but, if anything, the black crown of T. leucura is even less extensive than that of T. i. albitorques, and therefore, is not intermediate with respect to T. i. pelzelni.  If you scored the extent of the black crown as a character continuum, T. leucura would be at the “least black” end of the spectrum, and T. i. pelzelni would be at the “most black” end of the spectrum, with T. i. albitorques in between, although much closer to T. leucura.  So, I can’t really see any intermediacy in any of the characters that make the holotype of T. leucura unique.  Secondly, I would challenge the statement that the ranges of T. i. pelzelni and T. i. albitorques overlap in the area where T. leucura was collected.  As far as I’m aware, T. i. albitorques does not occur east of the rio Madeira, which is, after all, one of the most important biogeographical barriers in the Amazon Basin.  The subspecific range descriptions that accompany the T. inquisitor account in Fitzpatrick (2004) certainly do not indicate that T. i. albitorques extends across the Madeira, so I would be curious as to what the statement regarding overlapping ranges is based upon.  If T. i. pelzelni has a contact zone with any other subspecies east of the Madeira, it would seem to be with nominate inquisitor, somewhere in eastern Brazil.  In terms of the extent of the black crown, nominate birds are like pelzelni, and thus, once again, introgression between these two populations doesn’t support the assertion of phenotypic intermediacy.

 

We are left then, with Hellmayr’s concerns about the lack of pigmentation in the tail of T. leucura being an “abnormal” condition resulting from some developmental “absence of melanin”.  I can’t say much about this one way or the other.  It is certainly possible to conceive of an aberrant individual tityra that lacks black in the tail.  But, at the same time, Whittaker (2008) examined a large number of specimens of T. inquisitor from MZUSP and MPEG and failed to find another example of an entirely white-tailed individual.  The holotype had normal distribution of black in the wings and crown, and Hellmayr noted that the outermost pair of rectrices had “a narrow black shaft streak in the second third of the inner web, and a similar, but smaller spot of black near the base of the central rectrices.”  So, it’s not as if the holotype totally lacked melanin in the tail, nor did it show any pigment abnormalities elsewhere in the plumage.

 

Recommendation:  I’m a little on the fence on this one.  The only new evidence is a single detailed field observation (lasting 7 minutes) by an experienced observer, of a bird matching all of the important phenotypic characters of the holotype of T. leucura.  Unfortunately, there are no photographs or audio recordings documenting this observation.  However, it is noteworthy that Whittaker’s sighting came from the same biogeographic area (Madeira-Tapajós interfluvium) as the type locality.  It is also significant, I think, that this region remains under-explored, yet has been the source of several recent, previously undetected avian discoveries.  Recent fieldwork in the region has revealed that bird distributions, contact zones, and the ability of even seemingly minor rivers to act as biogeographic barriers are all much more complex than previously imagined.  I do not find it beyond reason to think that a canopy-dwelling, essentially cryptic (except for the white tail) species could escape detection for 140+ years.

 

I would also note that virtually each of the arguments put forth to dismiss the validity of T. leucura are the same ones made time and again to explain away named taxa that are known only from a single specimen – “hybrid”, “intergrade”, “mutant”, “unusual immature plumage” or some combination thereof.  Three examples come quickly to mind:  Hemitriccus inornatus, Conothraupis mesoleuca and Celeus spectabilis obrieni were all described from single specimens taken in relatively remote (at least at the time) parts of Brazil, and all “went missing” for long periods following their description (160+ years in the case of the Hemitriccus).  Prior to their rediscoveries, each of these three species was the object of much speculation regarding its validity, and, in each case, the hybrid, intergrade, mutant hypotheses were advanced.  We now know that all three taxa are valid.

 

Although the new field evidence is indeed thin, I think the re-examination it has provoked regarding the nature of the holotype of T. leucura reveals that there are enough holes in the arguments of Hellmayr, Ridgely & Tudor, and Fitzpatrick against T. leucura being a valid taxon, to return to the status quo of Pelzeln’s original treatment.  So, with mild hesitation, I would recommend a “YES” vote on recognizing the White-tailed Tityra, T. leucura, as a distinct species, as originally described by Pelzeln, 1868.

 

Literature Cited: 

 

Fitzpatrick, J. W. 2004.  Family Tyrannidae (tyrant-flycatchers).  Pp. 170–464 in del Hoyo, J., Elliott, A. & Christie, D. A. (eds.).  Handbook of birds of the world, vol. 9.  Lynx Edicions, Barcelona.

 

Hellmayr, C. E. 1910.  The birds of the Rio Madeira.  Novit. Zool. 17:257–428.

 

Hellmayr, C. E. 1929.  Catalogue of birds of the Americas and adjacent islands.  Field Mus. Nat. Hist. Publ. Zool. Ser. 13(6): 1–258.

 

Ridgely, R. S. & Tudor, G. 1994.  The birds of South America, vol. 2. Univ. of Texas Press, Austin.

 

Whittaker, A. 2008.  Field evidence for the validity of White-tailed Tityra, Tityra leucura Pelzeln, 1868.  Bull. B. O. C. 128(2): 107–113.

 

Kevin J. Zimmer, July 2014

 

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Comments from Remsen: “YES.  The proposal clearly outlines the issues, dismembers the previous arguments against valid species treatment, and properly acknowledges the lingering doubts generated by small N.  I have always had a bias against recognizing this as a real species because the other three Tityra are all so widespread that it would seem anomalous to have a rare, narrowly distributed species in the genus, and I suspect that this very point biased previous authors as well.  For similar reasons, I had always been suspicious of the validity Leptodon forbesi and Pithys castaneus, both of which we now know are obviously good species (and could be added to Kevin’s list of controversial, “lost” species).”

 

Comments from Pacheco: “YES.  The recent record of Whittaker pulled this old description of forgetfulness.  As noted by Van, this case also reminds me of the case of Leptodon forbesi: one (alleged) taxon of restricted distribution in the middle of another widely distributed. I am inclined at the moment to accept its existence of Tityra leucura.”

 

Comments from Robbins: “NO, but not because of the details that Kevin has provided. His assessment seems solid; however, I would want to see photos of the holotype (note that Kevin hasn’t examined the holotype), and although I don’t doubt Andy Whittaker’s observation, regardless of the party involved, it is a *sight* record.  I would want to have at least photographic documentation accompanying the report. Thus, until more concrete data are presented I would stick with treating “leucura” as Nomen dubium. Now that this has been highlighted by Andy’s observation and Kevin’s proposal, I suspect it will be unequivocally resolved in the not too distant future.”

 

Comments from Stiles: “NO, for the reasons advanced by Mark.  As he notes, the sight record is quite likely valid, but some tangible documentation does seem a requisite for including T. leucurus on the main list.  Now that attention has been drawn to this, hopefully evidence will soon be forthcoming!”

 

Comments from Nores: “NO, for three reasons. There are only 1 or 2 known specimens in 150 years; the short bill appears to have been retarded in its development and the white tail, can be a case of partial albinism.”

 

Further comments from Remsen: “I am changing my vote to NO.  The arguments of Mark and others has changed my view, as well as separate discussions with Bret Whitney.  I still strongly suspect that leucura is a valid species, but I acknowledge that the evidence is one step short of being completely convincing.”

 

Comments from Stotz: “NO. For the time being.  It may be real, but I think that we require more evidence than a sight record.  In all of the other cases mentioned as homologous, we do have that extensive additional evidence.  I think we should wait for it in this case.”