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." Fjeldså & 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 'hó-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.
Literature Cited:
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.
FJELDSÅ,
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 señalado buenas razones para
considerar que aequatorialis no es una especie diferente."