Proposal (73) to South American Classification Committee
Split Cacicus microrhynchus from C. uropygialis
Effect on South American CL: This proposal would split Cacicus uropygialis into two species, with recognition of Central American microrhynchus, including pacificus (Panama to Pacific slope Ecuador) as a separate species.
Background: The bird we treat as one species, Cacicus uropygialis has a disjunct distribution, with nominate uropygialis restricted to the subtropical zone of the Andes in a patchy distribution from W. Venezuela to C. Peru; microrhynchus occurs from E. Honduras to E. Panama, whereas pacificus is found from W. Panama south to El Oro, Ecuador. Both latter subspecies are restricted to the tropical zone.
Ridgway (1902) listed microrhynchus as separate from uropygialis. In his description of pacificus, Chapman (1915) describes it as similar in size to microrhynchus, but with larger bill, swollen at base. Measurements show a substantial difference in size from the larger uropygialis. He notes the following regarding the swelling at the base of the bill of pacificus and microrhynchus: "In others it is less prominent and it seems probable that the large and small-billed forms merge somewhere between the Canal Zone and the Colombian boundary." This suggests a possible cline between pacificus and microrhynchus. Measurements of uropygialis and pacificus show no tendency towards a cline between those two allopatric taxa, and appear distinctly different in size, even though pacificus is relatively large-billed. Hellmayr considered them all conspecific, with the following footnote: ""This form combines the general dimensions of C. u. microrhynchus with the powerful bill of C. u. uropygialis, thus occupying in its characters an intermediate position as it does geographically." Peter's Checklist (Blake 1968) puts all three taxa under uropygialis, without comments. Wetmore et al. (1984), noted difference in size between nominate and microrhynchus/pacificus, but mentioned that pacificus seems intermediate in bill shape and geographic position. Pacificus has a larger bill than microrhynchus, with the mandibular rami distinctly swollen. Wetmore et al. (1984) do note that an occasional male of microrhynchus shows a faint swelling on the outer face of the base of the mandibular rami, an indication of approach to the condition found in C. u. pacificus, but this is unusual. They also note that these two races are similar in size. Ridgely and Tudor consider all conspecific, but note that the lowland western taxa probably deserve species status, separate from the highland uropygialis. More recently, Ridgely and Greenfield (2003) considered pacificus a subspecies of microrhynchus, but both separate from uropygialis, as did Hilty (2003). We did the same, separating the lowland taxa from the highland taxon (Jaramillo and Burke 1999).
In terms of plumage the three taxa are quite similar, black with a restricted red rump patch. However it is in their size and structure that they differ noticeably. Other than in bill size, pacificus is similar to microrhynchus. On the other hand, uropygialis is substantially larger than the lowland forms, and is proportionately longer-tailed, whereas the microrhynchus group is proportionately longer-winged (absolute wing lengths still substantially smaller than in uropygialis though). Note that in turn all red-rumped caciques are quite similar, with the eastern lowland haemorrhous differing from uropygialis largely in size, proportions, size of rump patch, voice and strength of plumage iridescence. I don't think that the species status of haemorrhous has been questioned seriously in the literature.
New information: There isn't much new information per se, but there has been recent publication of the vocalizations of these taxa. Hardy et al. (1998) includes songs of microrhynchus, pacificus and uropygialis. More recordings of uropygialis are available on Moore and Lysinger (1997).
Analysis: The problem we have here is of taxa that are visually similar, which would not necessarily pop out at you as being but mere varieties of each other by looking at the museum skins. In real life the two groups, highland uropygialis and western lowland microrhynchus group are quite different. First, looking at what you would see in the museum skins the following is the case:
- uropygialis much larger than microrhynchus group. Uropygialis males: Wing 156.5 (145-165); tail 129.6 (107-142), culmen 30.8 (29-33); tarsus 33.0 (32 36). Microrhynchus males: Wing 129.0 (122.0-136.5); tail 89.7 (83.3 96.5); culmen 29.6 (28.8 30.2); tarsus 28.8 (27.4 ?). pacificus males: Wing 132.2 (122.2 137.2); tail 91.1 (87.8 94.9); culmen 29.6 (28.2-31.0); tarsus 29.5 (28.2 31.5).
- Structurally, uropygialis is very long-tailed. The microrhynchus group is relatively long-winged, something that is lost in the measurements due to their smaller size.
Second, are the behavioural and ecological differences.
- Uropygialis is quite consistently a species of the subtropical zone of the Andes, restricted to the east slopes south of Colombia. The microrhynchus group is found in the tropical zone, west of the Andes. The other component, if one enlarges this complex is haemorrhous, which is restricted to the tropical zone east of the Andes.
- Vocally the uropygialis and the microrhynchus group differ noticeably. Songs and vocalizations can be complex in this group, and certainly have a learnt component, other Cacicus species show noticeable changes in songs each year, and some are even mimics. Even so, it needs to be pointed out that the vocalizations of these two groups differ substantially, with uropygialis having more harsh and screechy notes, the microrhynchus group being more musical and pleasant. The exact structure and notes given in songs and other vocalizations differ clearly to the ear, but are extremely difficult to describe on paper. Calls are harsher in uropygialis, resembling haemorrhous more than the more pleasant and whistled notes of microrhynchus.
- Nesting behaviour and social structure is not well known for uropygialis. The smaller microrhynchus has a strong tendency to nest solitarily although small colonies are known, and has even been seen to have male help at the nest. Most unlikely cacique behaviour. Flocks of uropygialis tend to be larger than the pairs or presumed family groups of microrhynchus, suggesting that it may have a more standard cacique social structure. Hilty (2003) reports that uropygialis nests in small colonies.
What we have here is a situation that does not make much sense from a biogeographical stand point, a western lowland population is here lumped with a patchily distributed subtropical Andean taxon. No intermediates between the two are known, they are entirely allopatric. I imagine that the two forms may come relatively close geographically in parts of Colombia. Comments that the form pacificus may in fact be intermediate between microrhynchus and uropygialis are in error. The more southern pacificus is larger than microrhynchus, and supposedly proportionally larger in bill size (though my measurements do not bear this out), but in reality it is still a much smaller and shorter-tailed bird than uropygialis. Vocal differences between the two groups are clearly diagnosable, although the complexity of cacique voices makes comparison difficult. What I take to be clear differences in the call notes are suggestive of groups that have not been in contact for some time, assuming that the call notes are not learnt. The form pacificus has also been suggested to comprise a separate species (Ridgely and Tudor 1989) but this seems much more of a hard sell, particularly since little data is available on where the two come into contact, and all differences that have been noted could potentially be clinal. In fact, Chapman (1915) in his description of pacificus suggests that there may be an area where microrhynchus and pacificus merge into each other between the Canal Zone and Colombia. Ridgely and Greenfield (2001) do not propose species status for pacificus.
So we have two groups that differ in size and structure, voice, life zone that they inhabit and perhaps nesting behaviour and social structure. Early on they were considered different species, but were lumped more recently without any reasoning as to why this made sense. From my perspective on these caciques if you are going to put these two together, then you need to seriously consider why haemorrhous should not be lumped in as well. I don't think that lumping all red-rumped caciques is logical. I am just making the case that if taxa as different as uropygialis and the microrhynchus are lumped then why not lump all? The differences in voice, size, structure, and distribution of these taxa suggest that the lowland microrhynchus/pacificus pair should be split from the highland uropygialis.
Recommendation: YES – divide microrhynchus from uropygialis. Maintain pacificus as a subspecies in microrhynchus.
If we vote to split these two, using the Ridgely name Subtropical Cacique for uropygialis does work for me. It is one of the features that clearly separate it from all other red-rumped caciques. Note that microrhynchus has been known as "Small-billed Cacique" (Ridgway 1902), and this is an option, but retention of Scarlet-rumped Cacique for microrhynchus may be the way to go as this is the name that has been used recently by folks that are separating these taxa out. I don't know that microrhynchus is all that small-billed, it just is a small cacique.
BLAKE, E. R. 1968. Family Icteridae. Pp. 138-202 in "Check-list of birds of the World, Vol. 14" (Paynter R. A., Jr., ed.). Museum of Comparative Zoology, Cambridge, Massachusetts.
CHAPMAN, F.M. 1915. Diagnoses of apparently new Colombian birds IV. Bull. American Mus. Nat. Hist. XXXIV: 657-659.
HARDY, J.W., G.B. REYNARD, AND T. TAYLOR. 1998. Voices of the Troupials, Blackbirds and their Allies. ARA Records, Gainesville, FL.
HILTY, S. L. 2003. Birds of Venezuela. Princeton University Press, Princeton, New Jersey.
JARAMILLO, A. AND P. BURKE. 1999. New World Blackbirds, the Icterids. Princeton University Press, Princeton, NJ.
MOORE, J.V. AND M. LYSINGER. 1997. The bird of Cabañas San Isidro, Ecuador. John V. Moore Recordings, San Jose, CA.
RIDGWAY 1902. The birds of North and Middle America. Bull. U.S. Natl. Mus., 50, pt. 2.
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 G. TUDOR. 1989. The birds of South America, vol. 1. Univ. Texas Press, Austin.
WETMORE, A., R.F. PASQUIER, S.L. OLSON. 1984. The birds of the Republic of Panama, Part 4.
Alvaro Jaramillo, October 2003
Comments from Silva: "NO. I think that this set of arguments could be published before the change may be accepted."
Comments from Robbins: "YES. Long overdue".
Comments from Stiles: "NO, no properly published analysis. Having said this, I might add that I agree with the proposal, having had experience with all three in the field - if Alvaro wishes to publish a note incorporating measurement stats and sonograms, I will certainly go for it (might I suggest Ornitología Colombiana??)"
Comments from Zimmer: "NO. I agree completely with Alvaro that two species are involved. However, lack of any published analysis is the monkey wrench. I'd switch in a heartbeat if there was even a brief published analysis."
Comments from Nores: "NO estoy de acuerdo con considerar a Cacicus microrhynchus como especie y a pacificus como una subespecie de microrhynchus. Aunque las diferencias entre los caciques de rabadilla roja marcadas por Alvaro parecen válidas, antes de tomar una decisión habría que ver una nota publicada al respecto. Particularmente importante en su argumento pararse ser lo de las vocalizaciones y el hecho de que haemorrhous no difiere más de uropygialis que microrhynchus de uropygialis."
Comments from Remsen: "NO. Reluctantly. This is one of many in which our unpublished or qualitative knowledge strongly indicates that at least two species are involved. However, I regard our mission as evaluating published evidence for taxonomic changes, and with that mission in mind, the evidence is insufficient, in my opinion. Most of the evidence summarized by Alvaro is of interest and consistent with 2-species treatment, but in my opinion, also consistent with 1-species treatment, i.e., similar patterns of geographic variation exist within polytypic species, including Icteridae. The exception would be the vocal differences, but these are not formally described or presented. All that is needed for a YES vote from me on this is publication of sonograms of homologous vocalizations from critical areas."