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!) nor 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 Konig 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."