Proposal (282) to South American Classification Committee

Merge Geranoaetus into Buteo

Effect on SACC: This would merge monotypic Geranoaetus into Buteo.

Background & New information: Wetmore (1933) merged Geranoaetus into Buteo because he could find no way to diagnose the genus other than size. This was followed by some classifications (e.g., Hellmayr & Conover 1949, Friedmann 1950). Thus its close relationship to that genus had been recognized previously.

Geranoaetus melanoleucus has been maintained in a monotypic genus in recent classifications largely on the basis of Amadon (1963), who argued that it should be maintained as a separate genus because of its (1) relatively short ("although no more so than in one or two species of Buteo") and graduated tail, (2) somewhat unusual plumage, and (3) lengthened nape feathers. He concluded with "Although none of the characters mentioned is in itself decisive, taken together they make it desirable, or so it would seem, to keep Geranoaetus separate from Buteo. An equally important consideration is, as implied previously, that Geranoaetus may be closer to other South American buteonine genera, notably Buteogallus and Leucopternis, than it is to Buteo proper."

Riesing et al.'s (2004) analysis of mtDNA sequences placed Geranoaetus well within Buteo, in fact as the sister to Buteo polyosoma/poecilochrous (which makes some biogeographic sense). Although sampling additional genes and taxa may change the branching pattern somewhat, it seems unlikely that it will bounce Geranoaetus out of Buteo. Certainly, Amadon's hypothesis about a relationship to Buteogallus etc. is falsified.

Clark (2006) also favored a merger into Buteo, noting that is superficially similar to Old World Buteo rufofuscus and B. augur, and that historically, the main reason for maintaining it as a separate genus was its large size (hardly a genus-level criterion).

Analysis and Recommendation:

With the sole basis of maintaining this monotypic genus Amadon's statements, which he himself admitted are weak and represent a subjective opinion, and with genetic data placing it deep within Buteo, I see no reason to perpetuate this monotypic genus.

References:

AMADON, D. 1963. Comparison of fossil and recent species: some difficulties. Condor 65: 407-409.

CLARK, W. S. 2006. Melanistic specimen of Black-chested Buzzard-Eagle, (Geranoaetus melanoleucus) with comments on the species' taxonomic position. J. Raptor Research 40: 86-88.

RIESING, M. J., L. KRUCKENHAUSER, A. GAMAUF, AND E. HARiNG. 2003. Molecular phylogeny of the genus Buteo (Aves: Accipitridae) based on mitochondrial marker sequences. Molecular Phylogenetics & Evolution 27: 328-342.

WETMORE, A. 1933. Status of the genus Geranoaëtus. Auk 50: 212.

Van Remsen, June 2007

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Comments from Stiles: "YES. A mite sad to see Geranoaetus go, but there seems no valid reason to continue to recognize it with the solid evidence available that it's nested well within Buteo."

Comments from Robbins: "YES. Data are strong for placing Geranoaetus in Buteo."

Comments from Zimmer: "YES. Data seem clear, although I too will be sad to see Geranoaetus go."

Comments from Laurent Raty: "I would actually wait a bit before acting this move, for two main reasons:

"1) There is apparently a paper in press on this group (see http://www.lsa.umich.edu/eeb/people/mindell/publications.html).

"2) I'm not convinced this case is that straightforward.

"Riesing et al identified Geranoaetus as part of a group including B. polyosoma, B. poecilochrous and B. albicaudatus; in their tree, this group formed the most divergent branch of their "clade II", to which they attached the name Buteo. Among the taxa represented in the study, this clade included only 2 non-Buteo species... However, the study did not include any Leucopternis.

"In Lerner & Mindell (2005 - http://dx.doi.org/10.1016/j.ympev.2005.04.010), Fig 1 (cyt-b + nd2), Geranoaetus formed a trichotomy with Leucopternis albicollis, and a strongly supported clade grouping 2 other Leucopternis spp. (incl. melanops - the type of the genus) with two derived Buteo spp. (buteo and jamaicensis); in Fig 2 (cyt-b + nd2 + b-fib7), in the absence of a derived Buteo, Geranoaetus appeared basal to L. albicollis and L. melanops, suggesting it was the most divergent in the trichotomy of Fig 1.

"In Raposo et al. (2006 - http://dx.doi.org/10.1186/1471-2148-6-10), B. albicaudatus (a member of the Geranoaetus group identified by Riesing et al) appeared more distant to B. buteo (a derived Buteo) than two clades of Leucopternis, each one including 3 spp.; melanops was, again, part of the clade closest to the derived Buteo.

"Based on this, under Riesing et al.'s definition of Buteo, not only Geranoaetus, but also these 6 Leucopternis spp. (melanops, kuhli, semiplumbeus, albicollis, occidentalis, and polionotus) should all most likely be transferred to Buteo. And Leucopternis as a genus should simply disappear - *before* Geranoaetus, actually - because both studies indicate clearly that its type species is closer to that of Buteo than that of Geranoaetus... This may of course prove to be the best solution... But is it?

"It seems also possible, that an alternative solution might exist: restricting Buteo a bit more, e.g. to Riesing et al's "clade III", to keep all these Leucopternis out of it. This would bounce the whole Geranoaetus group out of Buteo (without actually affecting the branching pattern itself) but, based on present data, it is completely unclear that this would necessarily imply more moves than the first solution."

Comments solicited from Mike Braun: "I would agree with Laurent Raty's analysis. Although Geranoaetus will undoubtedly not survive, it is early yet to just lump it into Buteo. Better to wait to see a densely sampled and well-resolved multi-gene phylogeny. I predict we'll see a number of other New World buteonine genera come into play in deciding how best to treat this group taxonomically."

Comments solicited from Fabio Raposo: "I agree with Laurent and Mike`s points. Although there is no doubt that Geranoaetus is much closer to the more derived Buteo species than to the basal Buteogallus, the Leucopternis problem definitely brings some difficulties to this question. The evidence in Riesing et al 2003, Lerner and Mindell 2005 and in our 2006 paper taken together suggest that despite some of the Leucopternis species are basal and more closely related to "Buteogallus" (which also does not seem to be a good genus as currently recognized), two lineages appear nested within Buteo before Geranoaetus - as well stated by Laurent – the albicollis/polionotus/occidentalis clade and a second one including the Leucopternis type species (Leucopternis melanops). My concern about including Geranoaetus in Buteo is that automatically it would be necessary to include the entire above cited clades of "Leucopternis" within Buteo too - and forget Leucopternis completely, making Buteo a pretty large and heterogeneous genus. Although I fully agree that the genus Geranoaetus lacks a clear-cut diagnosis, definitely most non-monotypic Buteonine genera as currently recognized too – including Buteo. The bottom line is that including Geranoaetus melanoleucus in Buteo would require moving all the derived Leucopternis species to Buteo (changes in at least 6 species), while retaining Geranoaetus and keeping melanops/semiplumbeus/kuhli as Leucopternis would imply acting on Buteo albicaudatus and Buteo polyosoma, besides changing the Leucopternis albicollis/occidentalis/polionotus clade to another genus (at least 5 changes). Following any direction will require a lot of changes, but although we cannot be guided by clear diagnostic characters, restricting Buteo would at least make some biogeographic sense in my opinion - a mainly Nearctic and Old World Buteo, and the mostly Neotropical and basal species in their own genera."

Additional Comments from Remsen: "NO. The additional comments above lead me to change my recommendation and vote. Geranoaetus into Buteo would force the merger of so many genera into that genus that it would become disproportionately heterogeneous relative to other accipitrid genera."

Additional Comments from Robbins: "After reading Mike Braun and Fabio Raposo's comments I change my vote from "yes" to "no" for subsuming Geranoaetus into a catch-all Buteo."

Comments from Nores: "NO. Esto parecía fácil hasta que apareció el comentario de Raty y posteriormente los de Braun y Raposo. Por esta razón, pienso que hay que esperar a que aparezca el paper de Auk que está en prensa. Además, como sugerí en el caso de Paroaria, la propuesta debería haber incluido también el paso de Buteo leucorrhous a Percnohierax y Buteo magnirostris a Rupornis."

Comments from Jaramillo: "NO - Not yet at least, given the available evidence and opinions to do this now would create a veritable "lump fest" which would probably be undone with further data. I think we should wait and get more information on this issue. Nevertheless it is clear that Geranoaetus will be subsumed, but how the rest of the relationships within Buteo and Leucopternis amongst others are determined is key here."

Comments from Pacheco: "NO. Diante dos argumentos expostos por Raty, Braun e Raposo eu estou submetendo o caso para uma rediscussão também no CBRO. Por ora, com o presente cenário, eu creio ser prematuro a subordinação de Geranoaetus em Buteo."