Proposal (117) to South American Classification Committee
Lump Momotus aequatorialis with M. momota
Effect on South American CL: This would lump two species that we currently treat as separate into a single species.
Background: Chapman (1923, 1926) treated montane aequatorialis as a separate species from lowland M. momota, but recognized four species within what is currently considered M. momota. He based his species limits on Ridgway (1916) and his own synopsis of South American taxa by clustering them into plumage groups, although the rationale is generally vague. He noted that aequatorialis was more similar in plumage to Middle American lessonii, also a partly highland taxon. Although he seemed to attribute this to parallelism, he also seemed to consider them more closely related to each other than either is to lowland, intervening subrufescens.
Peters (1945) treated aequatorialis as yet another subspecies, without comments, in the highly polytypic M. momota complex, lumping all of Chapman's species into one. This was followed by Meyer de Schauensee (1966, 1970), Sibley & Ahlquist (1990), and AOU (1983, 1998). Sibley & Ahlquist (1990) noted:
"The aequatorialis group is distinct morphologically and ecologically and may prove to be a separate species, but some lowland forms appear to approach aequatorialis more than momota or subrufescens."
Parker, Parker, & Plenge (1982) treated aequatorialis as a form of uncertain species status. Hilty & Brown (1986) stated that aequatorialis is almost surely a separate sp." Fjelds & Krabbe (1990) remarked that aequatorialis (with chlorolaemus) "is almost certainly a high-elevation (semi)species." They provided no further information or discussion other than the plumage characters and elevational distribution of aequatorialis.
Ridgely & Greenfield (2001) treated aequatorialis as a separate species. They noted that there is roughly a 700 m gap between its lower limit in the eastern Andes (1000 m) and lowland Amazonian M. momota. They noted:
"M. aequatorialis is regarded as a species distinct from M. momotus, differing in its substantially larger size, voice, and montane habitat preference. Its nape band color resembles that of western M. m. argenticinctus, thus differing from that of M. m. microstephanus of the eastern lowlands."
The voice of M. aequatorialis was described as "Call a fast 'h-do,' closely similar to comparable call of e. slope Rufous Motmot [Baryphthengus martii]." The voice of M. momota was described as " ... a fast, hollow 'hooo-do,' similar to call of Rufous Motmot but with first note longer. Also gives a rolling series of less tremulous hoots. Western birds [argenticinctus] usually give a less separated 'whoooop," sometimes doubled." I have not listened to published recordings of these for a direct comparison.
Snow (2001) also treated M. aequatorialis as a separate species.
Analysis: Although at the outset, I was predisposed to accepting this split given everything I'd heard from field people about the distinctiveness of aequatorialis. But when it comes down to what's published, I have a hard time defending this split. The vocal difference sounds less than that between the two disjunct forms of M. momota in Ecuador. The elevational difference is impressive, but I would be much more impressed if they came in close contact without any gene flow. Furthermore, western argenticinctus occurs up to 1800 m on the west slope in Ecuador (Ridgely & Tudor 2001), so the elevational difference itself is bridged by a form treated as a subspecies of M. momota; in Ecuador, aequatorialis is found as low as 1000 m and as high as 2100 m. In Costa Rica, M. momota gets as high as 2150 m (Stiles & Skutch 1989). As for the size difference, that is the expected within-species trend for geographic variation on an elevational gradient. As for plumage, I do not see that the features of aequatorialis are generally any more distinctive than those of many of the distinctive subspecies in M. momota (see plate in Snow 2001).
Recommendation: I reluctantly vote YES on this proposal. Given the rather spectacular geographic variation in the M. momota complex, I am queasy about separation of one of the groups as a separate species, based on essentially no published evidence, while leaving the other taxa as a single species. I am eager to be dissuaded from that position.
CHAPMAN, F. M. 1923a. The distribution of the motmots of the genus Momotus. Bulletin American Museum of Natural History 48: 27-59.
CHAPMAN, F. M. 1926. The distribution of bird-life in Ecuador. Bull. American Museum Natural History 55: 1-784.
FJELDS, J., AND N. KRABBE. 1990. Birds of the High Andes. Zoological Museum, Univ. Copenhagen, Copenhagen, Denmark.
HILTY, S. L., AND W. L. BROWN. 1986. A guide to the birds of Colombia. Princeton University Press, Princeton, New Jersey.
MEYER DE SCHAUENSEE, R. 1966. The species of birds of South America and their distribution. Livingston Publishing Co., Narberth, Pennsylvania.
MEYER DE SCHAUENSEE, R. 1970. A guide to the birds of South America. Livingston Publishing Co., Wynnewood, Pennsylvania.
PARKER, T. A. III, S. A. PARKER, & M. A. PLENGE. 1982. An annotated list of Peruvian birds. Buteo Books.
RIDGELY , R. S., AND P. J. GREENFIELD. 2001. The birds of Ecuador. Cornell University Press, Ithaca, New York.
SIBLEY, C. G., AND B. L. MONROE, JR. 1990. Distribution and taxonomy of birds of the World. Yale University Press, New Haven, Connecticut.
SNOW, D. W. 2001. Family Momotidae (motmots). Pp. 264-284 in "Handbook of the Birds of the World, Vol. 6. Mousebirds to hornbills." (J. del Hoyo et al., eds.). Lynx Edicions, Barcelona.
Van Remsen, April 2004
Comments from Jaramillo: "NO _ My guess is that there may be more than two species involved in this complex. I am hesitant to lump something that is already on the list as separate given the variation in momota, and potential for even more species level taxa to be involved here. In other words, let's just go with it until new data comes out. Given that the status quo appears to be that these two species are different, let's keep it this way until new data comes out that confirms or refutes this hypothesis. The initial split may be based on little, but our lump would be based on little as well."
Comments from Stiles: "[YES] This is a tricky one for me, as I have been poking along on an analysis of Momotus in Colombia. I need to get more vocal data (sonograms) to round things off (and some time to write it all up), but FYI my main conclusions are the following: a) there are three species-level taxa of Momotus in Colombia: subrufescens of N and NW Colombia and the Magdalena valley (distinctive in morphology and voice) (this group also includes argenticinctus), aequatorialis (also morphologically and vocally distinct, although closer to the following than to subrufescens) and Momotus of E of the Andes. Both vocally and to some extent morphologically, aequatorialis is closest to the lessonii group of Central America, as Chapman noted long ago. Altitudinal distributions of momota and aequatorialis approach in extreme SE Colombia; I know of no real approach between aequatorialis and subrufescens (which seems adapted to hotter, drier habitats in any case). These conclusions are obviously unpublished and while on the basis of this work I would definitely vote NO, were I to vote solely on the basis of published evidence I would vote a very reluctant YES (as nobody else has published a thorough analysis either)."
Comments from Schulenberg: "YES. I think a case could be made for more than one species of Blue-crowned Motmot. But to my knowledge no such case exists in the recent literature. In fact, I was surprised to see that the SACC base list endorsed the split of aequatorialis from momota. I'd prefer to put everything back in one basket and wait until things get sorted out in a some more or less rigorous fashion."
Comments from Zimmer: "YES. This one is a tough one. While I think the split of these two is probably legitimate, I am bothered by the idea of singling out this one taxon, when the variation within the momota complex is obviously more complicated than a simple two-way, highland-lowland split. Like Tom, I'd prefer to see a complete overhaul of this group. Lacking this, I could support the piecemeal approach, but for this I'd prefer a stronger published rationale than what currently exists."
Comments from Silva: "NO. I agree with Jaramillo."
Comments from Robbins: "YES, to lumping these two forms. Although there are undoubtedly more than one species currently recognized within Momotus, clearly there needs to be a thorough treatment that takes into account all potential taxa in this complex before we start elevating various forms to species level."
Comments from Nores: "SI; pienso que Remsen ha sealado buenas razones para considerar que aequatorialis no es una especie diferente."