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.
Literature Cited:
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
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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."