Proposal (472) to South American Classification Committee

Recognize Thalurania nigricapilla as a valid species

The taxonomy of the trans-Andean members of the genus Thalurania has long been somewhat controversial. In NW Colombia and adjacent areas, two putative groups of taxa are now recognized as distinct species: the purple-crowned (in adult males) colombica group and the green-crowned fannyi group, based upon the study of Escalante & Peterson (1992). Their study involved only adult males, and the character that separated the groups completely was precisely crown color. However, other characters, particularly those of the females, may not support this split, as noted by Schuchmann (1999), who cautioned against “excessive reliance on crown color” in the classification of this group (with which I agree). Therefore, it is somewhat ironic that Valdés and Schuchmann (2009) have now described a new species in this group, based mainly upon crown color!

This putative new species is described as Thalurania nigricapilla on the basis of two male specimens. The type locality is the vicinity of Lake Calima (actually a reservoir) on the Pacific slope of the Western Andes of Colombia, some 50 km N of Cali at an elevation of ca. 1300 m. The paratype is from Alto del Toro near Yotoco at 1500 m, near the continental divide above the reservoir. Two taxa of the fannyi group are known from this general region: nominate fannyi from the lowlands and foothills of the Pacific slope, and subtropicalis from the eastern slope of the Western Andes and the western slope of the Central Andes (both sides of the upper Cauca valley) and, according to their paper, extending locally onto the Pacific slope NW of Cali, occupying higher elevations than fannyi. The two forms of fannyi are stated to differ in the more bronzy, less blackish nape and occiput and shorter, less deeply forked tail of subtropicalis compared to fannyi. Their new species is stated to differ from subtropicalis (and fannyi, although all detailed comparisons in their paper involve only subtropicalis) in the lack of a glittering green crown; both are described as having the crown and forehead as black, when viewed frontally. No female specimens are mentioned, although they describe a male of the putative species displaying to a female. They also compared the tail shape of the new form to that of subtropicalis, stating that it is longer and more deeply forked.

There are two reasons to question whether T. nigricapilla is a valid taxon. One is a series of specimens in the ICN labeled “Restrepo, Riobravo, Embalse de Calima, 800-850 m,” and the second is the possibility that the specimens of nigricapilla actually might represent old first-year males of subtropicalis – or fannyi. I have been informed that the expedition of the Instituto de Ciencias Naturales expedition to the Embalse de Calima in February 1984 had its base camp close to the reservoir itself, where the collecting was conducted; if so, because the reservoir itself is between 1200 and 1300 m elevation, the elevations on the specimen labels must be erroneous (the reservoir is in the jurisdiction of the town of Riobravo, which is at a lower elevation, so perhaps the elevations refer to the town and not the collecting site). In any case, it is the plumages of the male specimens in this series that are interesting: these include two adult males with fully green crowns, one possible adult with a mostly green crown but with some dull, blackish feathers on one side, and one immature male with a nearly fully green throat and chest but only a very restricted green area on the forecrown, most of the crown being dull dusky-bronze. Valdés and Schuchmann (2009) actually described the crowns of the holotype and paratype as “green-bronze” and “bronze-greenish forehead and bronze-colored crown and nape” respectively. Because virtually all of the iridescent feathering of hummingbirds looks black if viewed from an angle different from that of maximal reflectance, the description given for the new species as “black from frontal view” might be somewhat misleading depending upon the precise angle of viewing. Moreover, the green of the throat and chest of older first-year males (as well as the crown) is often less a pure green than a paler golden-green, evident in the immature male, and one of the putative adults has black feathering immediately adjacent to the bill on the anterior forehead. Thus, different birds in this series show varying degrees of approach towards nigricapilla. One of the adult males has a decidedly bronzy nape and occiput; the other has these areas more blackish, suggesting that this population may be to some degree intergrades between fannyi and subtropicalis (which in turn might explain the variability apparent in this small series). I note that very young immature males of the entire colombica complex lack iridescent feathering on the crown and have at best much duller green on the throat and chest confined to the feather tips giving a mottled appearance; the molt to a more adult-like plumage apparently begins soon after fledging (the young male described above has remnants of this plumage on the chest). The crown appears to molt somewhat later than at least the throat and anterior chest and the specimens of nigricapilla could well represent extreme cases of this - I note that in at least T. c. venusta, this is also the pattern of the adult males in their annual molt (see Stiles 1995). The males of this series also show variation in tail lengths and forks; one has a tail fork exceeding that of the one specimen of nigricapilla measured (the other lacked the outer rectrices), again suggesting the influence of fannyi. The other details of the color comparison between nigricapilla and subtropicalis do not rule out immaturity or influence of fannyi as well. I note that further south, according to the map of localities given by Valdés and Schuchmann, fannyi apparently reaches elevations similar to those from whence come the specimens of nigricapilla and could well extend up the deep valley below the Embalse de Calima to elevations at least approaching the reservoir. The description of a male nigricapilla displaying at and mounting a female is strikingly similar to what I have seen in young males of Calypte anna and a few other species; thus, play behavior of a young bird cannot be entirely ruled out.

A final reason why the status of nigricapilla as a valid species might be considered doubtful is the simple fact that in the limited area described for it occurs a second species of Thalurania virtually identical in morphology that surely would be a competitor for resources; I consider the evolution of such a species in sympatry with a potential congeneric competitor to be extremely unlikely and no other comparable case in hummingbirds occurs to me. Hence, I must conclude that without more evidence, ideally including a longer series of males of all ages as well as females, the evidence for considering nigricapilla as a valid taxon is inconclusive and I therefore recommend a NO vote on this proposal.

References

Griscom, L. The ornithology of the Caribbean coast in extreme eastern Panama. Bull. Mus. Comp. Zool. 72:303-372 (Pp. 334-337 include a review of the T. colombica complex as well as more data on subtropicalis, which is described on P. 337).

Stiles, F. G. 1995. Intraspecific and interspecific variation in the molt patterns of some tropical hummingbirds. Auk 112:113.132.

Valdes-Velásquez, A. & K.-L. Schuchmann. 2009. A new species of hummingbird (Thalurania, Trochilinae, Trochilidae) from the western Colombian Andes. Ornithol. Anz. 48:143-149.

F. Gary Stiles, October 2010

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Comments from Remsen: “NO. If this is indeed a valid taxon, then more specimens are needed. Thalurania are typically common and frequently netted, so obtaining more specimens should be easy. In addition to Gary’s excellent points, I also note: (1) N = 2 specimens; (2) even if a valid taxon, whether it should be assigned species rank is a separate question, because its diagnostic feature, crown color (in this case perhaps just an absence of iridescent feathers?), is one that varies among other taxa ranked at the subspecies level, at least within subspecies currently assigned to T. furcata – see the plate in Schuchmann’s chapter in HBW and look at T. f. nigrofasciata vs. T. f. baeri, for example. Resolving this one should be easy with a little more fieldwork.”

Comments from Nores: “NO. El hecho de que sean sólo dos ejemplares y que las características que definirían a esta nueva especie son variables, no soporta la validación de la misma, lo cual ha sido señalado con gran precisión por Gary. Además, resulta poco convincente describir a una especie sobre la base de una indicación tal como “negro desde una vista frontal”. Si los autores piensan que realmente se trata de una nueva especie, deberían capturar más machos adultos que muestren claramente las características que separan a la nueva especie.”

Comments from Robbins: “NO. Gary provides very solid comments for questioning the validity of this taxon.”

Comments from Zimmer: “NO. The case for “nigricapilla” being a distinct species appears weak at best, for reasons nicely summarized by Gary. I echo Van’s comments, both with respect to N, and as regards reliance on crown color. And, I think Gary’s final paragraph regarding sympatry of the proposed new species with a nearly identical presumed ecological competitor really hits the nail on the head. This flies in the face of the essentially allopatric species-distribution pattern of Thalurania.”

Comments from Graves: “Gary's summary nicely outlines the problems with the supposed new taxon. The two specimens of "Thalurania nigricapilla" were collected by Professor Schuchmann in 1978 and deposited in Bonn. During the subsequent decades, Schuchmann published many dozens of papers on hummingbirds. The fact that they were undescribed for 30 years suggests that he didn't ascribe any unusual significance to their appearance until recently. I have not examined the specimens, but plumage descriptions suggest they represent young males in prebasic molt or in first basic plumage. Wing length (about 4 mm shorter than Thalurania furcata subtropicalis) also suggests a subadult plumage. The authors did not mention the presence or absence of fine striations on the maxillary ramphotheca. These would almost certainly be present in specimens in juvenal plumage and in many specimens undergoing prebasic molt. Most species in that clade lack striations in first definitive plumage, however, so the absence of striations does not necessarily indicate "adult" plumage. Why aren't they subadult (or aberrantly plumaged) Thalurania furcata subtropicalis? In any event, the age class of the specimens is unclear and this ambiguity lobbies against the recognition of the proposed taxon. This issue should be relatively easy to resolve with a few days of mist-netting at the type locality.”

Comments from Pacheco: “NO. A validade do táxon nigricapilla não pode ser assumida a partir dos questionamentos bem construídos por Gary. A julgar pelo conhecimento em Thalurania, as possibilidades de validade do táxon são de fato muito reduzidas.”

Comments from Cadena: “NO. Gary Stiles's arguments are persuasive, and as indicated by Van and Gary Graves, a few days worth of fieldwork in the area would go a long way towards resolving the issues. I visited the Rio Bravo area in 1998 and have Thalurania in my notes as being common then.”

Comments from Jaramillo: “NO. It is prerequisite to have more specimens from this locality to determine if this is indeed a new taxon, or an age class, individual variation or subspecies. Definitely more fieldwork is necessary.”