Proposal (49) to South American Classification Committee

 

Split Trogon chionurus from T. viridis

 

Effect on South American CL: This proposal would elevate a taxon to species rank that we currently treat, by implication, as a subspecies on our baseline list.

 

Background: For most of its history (e.g., Peters, Meyer de Schauensee, Sibley & Monroe 1990, Collar 2001), the taxon chionurus has been treated as a subspecies of Trogon viridis (White-tailed Trogon). They are allopatric taxa with no known contact zone, although they come close in N Colombia. Chionurus is the trans-Andean taxon, found from E Panama south to W Ecuador and also N Colombia in the Cauca and Magdalena valleys, whereas nominate viridis is widespread east of the Andes. A third taxon (melanopterus) is isolated in southeastern Brazil, Bahia to S‹o Paulo, presumably an Atlantic forest taxon, but it was not recognized as a valid subspecies by Collar (2001). [By the way, the range map in Johnsgard's book on trogons blows this completely.] Chionurus and nominate viridis are presumably 100% diagnosable phenotypic units based on plumage characters, mainly differences in the amount of white on the underside of the tail (e.g., see plate 47 in Ridgely & Greenfield 2001).

 

New information: Ridgely & Greenfield (2001) considered chionurus a separate species from viridis based largely on voice. They described chionurus song as a "very fast series of 15-20 'cow' or 'cowp' notes with characteristic acceleration toward the end, when it also drops in pitch." A very similar description, presumably based on birds from E Panama, is given in Ridgely & Gwynne (1989): "a series of rather soft coo notes, repeated slowly at first, then accelerated into a roll, sometimes ending with slower notes."

 

In contrast, Ridgely & Greenfield (2001) described Amazonian viridis as: "a fast, fairly even series of 15-20 'cow' or 'cowp' notes ...." Thus, the difference is in the inter-note spacing, fairly constant in viridis but progressively decreasing in chionurus.

 

The problem is that Hilty & Brown (1986) gave essentially the opposite description: [nominate] "a series of brisk kyoh or cow notes (up to 16 or so), usually accelerating (or no acceleration -- chionurus) and becoming louder near end, sometimes with a few slower cow's at end." I assumed this was just a lapsus, an inversion. But then Hilty (2003) described viridis from Venezuela as giving two song types, one fast and one slow, evidently depending on presence/absence of Trogon violaceus, and described the fast song as: "typically starts hesitantly, then gains speed and confidence, caaop, caaop, caao--cao-ca-ca-ca-ca-ca-ca-ca-ca-ca-ca." Thus, the Venezuelan population of nominate viridis would appear to have an accelerating song, which Ridgely & Greenfield considered restricted to chionurus.

 

Analysis: These discrepancies were sufficient to keep me from digging out actual recordings from "Hardy" tapes, Schulenberg Peru CDs, etc., to determine on my own what and where the problem is. If there is that much variation in qualitative descriptions, then I see no point in pursuing this casually -- clearly, a thorough analysis is needed. There indeed may be two or more species-level taxa in viridis, but that requires a thorough analysis of song from throughout the ranges of the taxa, including disjunct "melanopterus," which I suspect many of us would bet is at least as distinctive as is chionurus.

 

Recommendation: I vote "NO" on this proposal because not even the qualitative descriptions match up. The disjunct Atlantic forest population also needs to be included. Let's get this straightened out properly before changing species limits.

 

Literature Cited:

COLLAR, N. 2001. Family Trogonidae (trogons). Pp. 280-479 in "Handbook of the Birds of the World, Vol. 6. Mousebirds to hornbills." (J. del Hoyo et al., eds.). Lynx Edicions, Barcelona.

HILTY, S. L. 2003. Birds of Venezuela. Princeton University Press, Princeton, New Jersey.

HILTY, S. L., AND W. L. BROWN. 1986. A guide to the birds of Colombia. Princeton University Press, Princeton, New Jersey.

RIDGELY , R. S., AND P. J. GREENFIELD. 2001. The birds of Ecuador. Vol. II. Field guide. Cornell University Press, Ithaca, New York.

RIDGELY R. S., AND J. A. GWYNNE. 1989. A guide to the birds of Panama, with Costa Rica, Nicaragua, and Honduras (2nd ed.). Princeton Univ. Press, Princeton, New Jersey.

SIBLEY, C. G., AND B. L. MONROE, JR. 1990. Distribution and taxonomy of birds of the World. Yale University Press, New Haven, Connecticut.

SICK, H. 1993. Birds in Brazil. Princeton Univ. Press, Princeton, New Jersey.

 

Van Remsen, August 2003

 

P.S.: If the proposal does pass, then I'll work on another one on the English names of these two.

 

===========================

 

Comments from Zimmer: "I vote "NO" on splitting T. chionurus from T. viridis, although this vote is a somewhat reluctant one. I have no doubt that these two are separate species. Songs of chionurus are very distinctive in their acceleration, and are reminiscent of T. melanocephala of Mexico to Costa Rica. Songs of viridis throughout most of Amazonia are very different (more evenly paced series of COW notes). That having been said, I find that trogon voices in general in South America are notably tricky and are somewhat variable both within and between populations. In Costa Rica, where 9 species of Trogon occur, I have no problems in identifying birds to species by voice, except for aurantiiventris from collaris, and many people (including AOUCC?) consider them to be conspecific anyway. In S America, I find the situation much different. When working a new site in the Amazon, I find that I often have to recalibrate my ear for each of the species to adjust to variation in pacing and pitch. Much of this variation is subtle, but there is variation nonetheless. In the case of viridis, there  is also a problem with the disjunct E Brazilian population melanopterus, which sounds different from Amazonian/Guianan birds (albeit not as different as chionurus). In sum, although I think Ridgely is right-on with respect to splitting chionurus, I'm not convinced that a simple trans/cis Andean split is the final word. Although I generally prefer to see the whole complex dealt with at once, I could still be persuaded to tackle it piecemeal if in fact there was a thorough published analysis supporting the split. In the absence of such an analysis, I'd prefer to wait. "

 

Comments from Schulenberg: "My vote: No. It would not surprise me if this proposal were valid, but, as Kevin Zimmer notes in his comments to this series of proposals, trogon voices can be tricky. In any event, I'd prefer to wait until there is more of an analysis (even a simple minded one) for us to go on.

 

"[What, by the way, is the "deal" with Central American collaris? My limited experience in Costa Rica is the same as Kevin's, that collaris and aurantiiventris sound the same (and so "must be" the same species); but Costa Rican collaris/aurantiiventris sound different from Amazonian collaris. Am I not remembering these voices correctly? Or if there *is* a difference between Costa Rica and Amazonian collaris, then where is the "break"? Neither Hilty and Brown (Colombia) nor Ridgely and Greenfield (Ecuador) mention a difference in voice in collaris across the Andes. Yet another complex that someone should analyze in more detail? ]"

 

Comments from Zimmer: "Although Ridgely et al. are likely correct, I agree with Van that a detailed analysis of vocalizations from throughout virdis' range is needed before making a change. Hence, I vote "no"."

 

Comments from Stiles: "Trogon splits. NO to all, until all the evidence is in and published. Two or three will probably prove correct, but at this time we don't have enough solid evidence to accept them."

 

Comments from Jaramillo: "NO _ Need for a thorough analysis of voice, particularly given the discrepancies in the literature. I do appreciate that there may be at least two species here, but I do want a note or paper somewhere to make it official. "

 

Comments from Silva: "No. I agree that a detailed study including all populations of this taxon is needed before to propose any taxonomic change."

 

Comments from Nores: "[NO] No estoy de acuerdo en separar a Trogon chionurus de T. viridis. Separar especies por suaves diferencias en el canto no me parece bien, como ya lo expresˇ en el caso de Rhynchotus rufescens maculicollis. Recientemente estuve en el noreste de Brasil y me llam— la atenci—n lo diferente que son los cantos de algunas subespecies de all’ con respecto a las poblaciones del sur de Sudamˇrica. Por ejemplo, Thraupis sayaca tiene un canto mucho m‡s potente y m‡s variado que las razas del sur, y Turdus rufiventris emite un llamado permanente que nunca se la escuchˇ a la subespecie de esta latitud. Otro ejemplo del sur es Vanellus chilensis, la raza del sur de Argentina y Chile emiten un canto bastante diferente (parece un loro) que la raza que habita el norte y centro de Argentina. Tanto es as’ que muchas personas (no ornit—logas) me preguntan quˇ a que se debe que las aves del sur cantan tan distinto Esto no significa para m’ que haya que elevar las subespecies a especies."