Proposal
(328) to South American
Classification Committee
Elevate Bubo
v. magellanicus (Strigidae) to species level
Effect on South American CL: This proposal would elevate a taxon
to species rank that we currently treat as a subspecies.
Background: König et al. (1996) proposed, based on
differences in voice, size, and molecular data, that the southern Andean and
Patagonian magellanicus be elevated to species status from the widespread
virginianus. Marks et al. (1999) and others followed this treatment
without any additional insight, i.e., they repeated what was in König et al.
(1996). However, Schulenberg et al. (2007) followed traditional treatment
(Traylor 1958) of magellanicus, because of purported intergradation and
individuals giving vocalizations of both forms in northern Peru.
Analysis: Magellanicus is very similar in plumage to other virginianus
taxa, except for having shorter ear tufts and apparently being smaller in
size (mass, wing, tail, bill; Traylor 1958). However, as the always-thorough
Mel Traylor noted, the northern Andean magellanicus population (central
Peru, Bolivia) apparently is larger than southern populations (he noted that
this may be an altitudinal effect) and overlaps in size with nigrescens of
northern Peru, Ecuador, and Colombia. If North American populations are any
indication on the relevance of morphology, then plumage pattern and size have
little bearing on species limits. For example, within North America the eastern
nominate subspecies is boldly marked and richly colored, whereas birds in the
drier western portions of North America are relatively pale with less distinct
markings. These two subspecies freely interbreed where they come together in
the western Great Plains. Some individuals of northern wapacuthu are so
white with black barring that they resemble immature Bubo scandiaca!
Finally, darkest populations are found at the opposite sides of the continent.
Although not as extreme, morphological variation is considerable among
described forms in Central and South America. Therefore, plumage differences
have little to no merit in defining species limits within this group.
As one would predict, the primary vocalization is likely the key
in species recognition, and although plumage variation is considerable within
North American populations, there is very little vocal differentiation. In
contrast, the song of birds referable to magellanicus in the
central and southern Andes and Patagonia is quite distinct from that of birds
north of the Marañón Valley in Peru and birds in the eastern lowlands of South
America north of northern Argentina. The song of magellanicus consists
of two deep hoots with emphasis on the second note, followed by a low guttural
purring: "bu-hóohworrrr", whereas the typical song of virginianus consists
of two or more notes and lacks the ending purr (König et al. 1999, pers. obs.,
see Xeno-canto and Macaulay Library of Natural Sounds, Cornell Laboratory of
Ornithology [MLNS] websites).
König et al. (1999) stated that magellanicus and the
subspecies of virginianus (nacurutu) found locally east of the Andes,
are at least parapatric in northwestern Argentina (depto. Salta): "where
the lowlands and foothills are occupied by B. v. nacurutu while
in the rocky "quebradas" and above timberline (3,000-4,000 m) B.
magellanicus is found." To my knowledge, there is no published
information on the potential contact of these two taxa elsewhere in Argentina.
The recently published Birds of Peru (Schulenberg et al. 2007) offered
insight into contact between magellanicus and nigrescens (Andes
of Colombia, Ecuador and northern Peru), stating that magellanicus may
intergrade with nigrescens in northern Peru. Recordings by the late Ted
Parker from Piura, Peru (MLNS 21879-80, 21890; listen to these on the MLNS
website) appear to indicate birds giving both call types.
König et al. (1996) compared 960 base pairs of mitochondrial cyt-b sequence
data of virginianus with magellanicus and found that they differ
in nucleotide substitution by 1.6 %. However, there is no indication of sample size
(presumably one of each!) or locality data for the samples. Thus, it is unclear
what population of virginianus was compared with magellanicus. In
other words, data presented in that paper are meaningless without accompanying
pertinent information.
Recommendation: Although there may be more than one species
within the virginianus complex, to date, data are minimal and undocumented.
What is needed is a thorough vocal and genetic analysis of the entire group,
especially in key areas in northern Peru and northern Argentina (southeastern
Bolivia?), before we change the current treatment. Hence, I
recommend a "no" vote.
Acknowledgments: Tom Schulenberg provided a copy
and Árpad Nyári helped with translation of the König et al. 1996 paper. Niels
Krabbe and Dan Lane provided pertinent vocalizations and valuable insight.
Literature Cited
König, C.,
P. Heidrich, and M. Wink. 1996. Zur Taxonomie
der Uhus (Bubo ssp.) im südlichen Südamerika. Stuttgart. Beitr.
Naturk. Ser. A, 540
König, C.,
F. Weick, and J-H. Becking. 1999. Owls. A guide to the owls of the world. Pica
Press, Sussex, England.
Marks,
J.S., R.J. Cannings, and H. Mikkola. 1999. Family Strigidae (typical owls). Pp.
76-243 in: del Hoyo, J., Elliott, A. & Sargatal, J. eds. (1999). Handbook
of the birds of the World. Vol. 5. Barn-owls to Hummingbirds. Lynx Edicions,
Barcelona.
Schulenberg,
T.S., D. F. Stotz, D. F. Lane, J. P. O'Neill, and T. A. Parker, III. 2007.
Birds of Peru. Princeton Univ. Press, Princeton, New Jersey, USA.
Traylor,
M.A. 1958. Variation in South American Great Horned Owls. Auk 75:143-149.
Mark
Robbins, January 2008
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Comments from Remsen: "NO, for all the reasons
stated by Mark. I would also add that from Mark's description of the König et
al. analysis, it does not fit the definition of "science" because one
could not replicate it."
Comments from Stiles: "NO. Again, I agree with
Mark that the evidence currently available does not justify recognition of magellanicus
as a species - particularly as the molecular data are suspect and, as Van notes
unrepeatable."
Comments from Stotz: "NO. I think that there are
way too many questions still about the relationship between magellanicus
and virginianus. I await better data on voice and genetics before going
for this split."
Comments from Zimmer: "NO. As Mark correctly
points out, the morphological distinctions between magellanicus and
the rest of the virginianus group are not as great as the variation
within the rest of virginianus. Clearly, there is something going on
vocally with respect to the two groups, but the published evidence really
doesn't clarify just what that is. Although I suspect that there are two good
biological species involved, on current evidence it is not clear where the
geographical boundaries are, nor even what the true vocal differences
are."
Comments from Nores: "NO. Las razones dadas por Robbins y la añadida por Remsen muestran
claramente de que el trabajo de König et al. no es suficiente, por el momento,
para separar las subespecies en especies."
Comments from Jaramillo: "YES - I will be the
contrary vote on this one, perhaps because magellanicus is a bird I
have a lot of experience with throughout Chile, and to me it seems much more
distinct vocally and morphologically from virginianus than many Glaucidium
taxa. Size is not the only distinction from virginianus; it also has
rather small talons, sort of like the difference between Whiskered and Western
Screech-Owls. The voice of magellanicus is absolutely always the same in
Chile, from Tierra del Fuego to the border with Peru, and is consistently
different from that of virginianus. Perhaps they hybridize in northern
Peru with nigrescens, perhaps they do not, and a bit of hanky-panky
between related species is not unheard of, so that does not trouble me. I do
think it is worth figuring out what nigrescens is, and what is
going on there though. In northern Argentina, the lowland birds are vocally
indistinguishable to my ears from North American virginianus. So we have
these two vocal groups that are found over vast areas of the American
continent, they seem to show little or no geographic variation, and they appear
to be parapatric in at least one area (Salta, Argentina) with one being a
lowland form, the other a highland form. This is the classic pattern of two
good biological species. Granted that there may be something more complex going
on in northern Peru that does not invalidate the big picture. This is
independent of any dubious genetic work done by König.
"Some additional notes on magellanicus. In
southernmost Chile this owl seems to show a distinct preference for Tuco-tucos
(Ctenomys). It is also fond of nesting on the ground, and it is common
to find it relatively active during the day. I have played virginianus tape
to birds in Chile just out of curiosity and they completely ignore the tape.
Farther north the species is much less common, particularly in the central zone
as it shuns forest. In the far north it is found in various open areas, often
near cliffs for nesting, including desert valleys and ravines within the lower
Puna. I should ask Dan Lane what the habitats are like in this possible area of
intergradation."
Comments from Cadena: "NO. Alvaro's points are
well-taken, but we should wait until the relevant data have been analyzed in
detail and presented in a publication."