Proposal (#50) to South American Check-list Committee:

Split Trogon caligatus from T. violaceus


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 their recent history (e.g., Peters 1945, Meyer de Schauensee, Sibley & Monroe 1990, Collar 1996), the taxon caligatus has been treated as a subspecies of Trogon violaceus (Violaceous Trogon). Ridgway (1911) and Cory (1919) did treat them as separate species. They are allopatric taxa with no known contact zone, although they must come close in W Venezuela; in fact, the gap there might be shorter than that between the two disjunct populations of the subspecies concinnus - there is a gap in its distribution in W Colombia separating populations of E Panama and NW Ecuador. The caligatus group (with sallaei = braccatus, and concinnus) is the trans-Andean taxon, found from Mexico south to NW Peru **, and also across lowland N Colombia into NW Venezuela, whereas the nominate violaceus group (with ramonianus and crissalis) is widespread in Amazonia east of the Andes.

The caligatus and nominate violaceus groups are almost ertainly 100% diagnosable phenotypic units based on plumage characters, but the difference is much less than that between the White-tailed Trogon groups of Prop. 49, mainly the color shade of the nape and crown, more blackish in caligatus (e.g., see plate 47 in Ridgely & Greenfield 2001). The problem is that Hilty (2003) stated that, although the subspecies of the violaceus group that comes closest to caligatus geographically, T. v. crissalis, differs slightly in head color ("dark blue" vs. "purplish blue"), nominate violaceus itself, from farther east in Venezuela, is "essentially identical" to caligatus (male and females). Collar 's (1996) descriptions of the six subspecies indicate that each has diagnostic a diagnostic combination of head color, wing-covert pattern, and tail color, but they do not seem to break cleanly into two groups, with head color, for example, showing a somewhat mosaic distribution pattern (blackest in northernmost sallaei and in distant, Amazonian, crissalis, and nominate violaceus and caligatus being essentially the same purplish blue).

New information: Ridgely & Greenfield (2001) considered caligatus a separate species from violaceus based largely on voice. They described caligatus song (presumably concinnus from trans-Andean South America) as a "an even, rather fast, and long series of relatively high-pitched 'ca' notes steadily repeated without a break, often 20 or more notes in a song."

In contrast, Ridgely & Greenfield (2001) described Amazonian violaceus (presumably ramonianus or crissalis from E Ecuador) as: "fast but relatively short series of clipped 'cow' notes, the notes often becoming doubled ('cadow-cadow-cadow ... ')." Thus, violaceus song is described as faster with a tendency towards doubling of notes.

Other descriptions of songs from the caligatus group are as follow:

(a) Ridgely & Gwynne (1989), presumably based on birds from Panama (concinnus or caligatus): "a series of soft cow notes or sometime kyoo notes, repeated steadily 10 to 15 times ... ."

(b) Stiles & Skutch's (1989) description from Costa Rica (concinnus): "a long series of clear, downslurred whistled notes on the same pitch" Kwer kwer kwer kwer ..., or kew kew kew ... ."

(c) Howell & Webb's (1995) from Mexico (braccatus = sallaei): " a fairly rapid, persistent, hollow hooting, kyow-kyow-kyow ... or ku-ku-ku..., 10/2.5-3 s, may suggest Ferruginous Pygmy-Owl."

(d) Hilty (2003), who followed the Ridgely-Greenfield split, described caligatus song from NW Venezuela as: "a rather fast series of down-slurred whistled notes, cuh-cuh-cuh ..., at steady rate (no acceleration) of ca. 3/sec and 7-20 or more notes."

Whether these songs are virtually identical and this variation is simply an artifact of the problems of qualitative song descriptions, or whether the variation is real cannot be answered without careful analysis of sonagrams.

[Hilty & Brown's (1986) description from Colombia ("a series of up to 15 rather soft cow or cuh notes .., about 2 per sec") was not identified to locality, but sounds more like Ridgely & Greenfield's caligatus.]

As for descriptions of songs from the violaceus group, I got as far as ....

(a) Hilty (2003) described violaceus song in Venezuela as "up to 15, occas. to ca. 35, rather soft cow or cuh notes, faster (at least 2/sec up to nearly 4/sec) ... ." Also: "Some w. Amaz. pops. (Venez.?) of this sp. show marked variation in song speed, acceleration, etc." [No doubling of notes is mentioned.]

After reading this last statement, I quickly lost interest, as in Prop. 49, and decided that untangling this would not be solved by listening to CDs etc. -- clearly this is a complicated situation that does not lend itself to comparisons of qualitative descriptions from here and there.

Analysis: As with the Trogon chionurus/viridis situation, I do not think its my duty to pull out "Hardy" tapes, Schulenberg Peru CDs, etc., to determine on my own whether there are really two major song types (or not), or more. If there is that much variation in qualitative descriptions, then I see no point in pursuing this casually -- clearly, a thorough analysis must be undertaken. There indeed may be two major, species-level taxa in violaceus, as treated by Ridgway (1911), clearly demarcated by song types, as Bob proposed, but qualitative comparisons are not the way to handle this. My now-dim recollections of trogon song is that the inter- and intra-population variation can be tricky, so I look forward to comments from all of you with recent field experience.

Recommendation: I vote "NO" on this proposal because before changing species limits in this widespread group, song types and their constancy needs to be sampled and compared quantitatively throughout the ranges. Even if the differences between the two groups are dramatic but just insufficiently described above, they nonetheless require further published, more convincing documentation.

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.

HOWELL, S. N. G., AND S. WEBB. 1995. A guide to the birds of Mexico and northern Central America. Oxford Univ. Press, New York.

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.

RIDGWAY, R. 1911. The birds of North and Middle America. Bull. U. S. Nat. Mus., no. 50, pt. 5.

STILES, F. G., AND A. SKUTCH. 1989. A guide to the birds of Costa Rica. Cornell Univ. Press, Ithaca, New York.

Van Remsen, July 2003

** The sloppiness of the maps in Johnsgard's trogon book is impressive, with all of trans-Andean South America omitted.

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. caligatus from T. violaceus. Once again, my vote is a reluctant one, because I think Bob has it basically right. The voice of caligatus group (including braccatus and concinnus) is a long, fast-paced series reminiscent of a Ferruginous Pygmy-Owl, or, sticking with trogons, of Amazonian populations of T. curucui. By contrast, T.v. ramonianus and T.v. crissalis of western and southern Amazonia have quite different voices, with notes often doubled. Much of the apparent confusion in published description of voices is, I think, attributable to the combination of inherent differences in how different authors qualitatively describe voices, and from the careless practice of authors sometimes attributing the voice of a bird from one region to the same "species" in another region (this applies to the inconsistencies in descriptions of voices in the viridis complex mentioned in Proposal #49 as well). This having been said, I think that once again the situation may be more complex than a simple 2-way split. I do not have tapes in front of me, but my recollection is that the song of nominate violaceus from Venezuela is closer to that of birds in the caligatus group, and unlike those of W and S Amazonian populations. I hesitate to float this idea without listening to tapes, but in any event, the basic premise still applies: I think that the vocal variation within the species is more complex than a simple 2-way split (or at least not precisely the 2-way split that is proposed), and in the absence of a thorough published review of the vocal differences, I think it is better to wait this one out."

Comments from Schulenberg: "My vote: No. It would not surprise me if this proposal were valid, but I'd prefer to wait until there is more of an analysis (even a simple minded one) for us to go on."

Comments from Robbins: "No - Ditto with my comments for proposal # 49."

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. Kevin's notes suggesting that even if the split is good, that the division may be in a different place than suggested by Ridgely and Greenfield is further reason to ask for a thorough analysis before making the split."

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. Idem a 49."