Proposal (#377) to South American Classification Committee
Merge Geranoaetus into Buteo
Effect on SACC: This would merge monotypic Geranoaetus into Buteo.
Background & New information: A previous proposal for this major was defeated in 2007. See that proposal (282) for a synopsis of previous arguments pro and con. The rationale for rejecting the proposal was largely that the first genetic study sampled only 1 gene and relatively few taxa, and that additional sampling might change the picture.
Since then, a new gene-based phylogeny has been published (Lerner & Mindell 2008) that provides strong support for the merger of Geranoaetus into Buteo. This study analyzed > 3000 bp of mtDNA and nDNA of most New World buteonines ... thus a multiple gene analysis with dense taxon-sampling. Strong support (Bayesian support 1.00) was found for a sister relationship between Buteo polyosoma (including poecilochrous) and Geranoaetus, with B. albicaudatus sister to these two (Bayesian support 0.96). Therefore, maintaining a monotypic Geranoaetus is no longer tenable under basic principles of phylogenetic classification.
As an aside, also note the general similarity in biogeography and habitat between B. polyosoma and Geranoaetus.
Analysis and Recommendation: The only other option would be to merge three species of reasonably typical (in morphology) buteos into Geranoaetus. However, because this group is at the base of the tree that includes the rest of the buteos except Buteo magnirostris and B. leucorrhous (both of which merit serious consideration as monotypic genera separate from Buteo), an alternative would be to expand Geranoaetus to include polyosoma and albicaudatus. Note that Leucopternis albicollis, L. polionotus, and L. occidentalis fall deeper within the Buteo branch, and so to retain a broadly defined Buteo, these three must also be merged into Buteo ... but that will be the subject of a separate proposal. Under our current classification, with a broadly defined Buteo, Geranoaetus must be merged into Buteo.
References: (see also 282)
LERNER, H. R. L., AND D. P. MINDELL. 2008. Molecular phylogenetics of the buteonine birds of prey (Accipitridae). Auk 125: 304-315.
Van Remsen, November 2008
Comments from Zimmer: "YES, for reasons stated in the proposal. I am dismayed to think that this will ultimately mean merging various Leucopternis into Buteo, which was something of a deal-breaker for the Geranoaetus merger the first time around."
Comments from Robbins: "YES, Yes, the genetic data do seem to be unequivocal about including Geranoaetus in Buteo."
Comments from Stiles: "YES, as we have effectively opted for maintaining a broad Buteo, genus Geranoaetus must go (as, presumably, should the several Leucopternis embedded in Buteo). Given the large number of species and worldwide distribution of Buteo, it eventually might be desirable to break the genus up but this would probably require virtually complete taxon sampling of Buteo and some related genera around the world - although good, taxon sampling in the Lerner & Mindell paper still comes up a bit short on this score."
Comments from Nores: “NO, porque decir SI también implica (en base a Lerner et al. 2008), aceptar que Rupornis es un género diferente y que algunas especies de Leucopternis están incluido dentro de Buteo y otras no. En otras palabras la propuesta debería ser más amplia y algo así podría ser la secuencia:
Buteo (grupo melanoleucus)
Buteo (grupo Leucopternis 1)
Buteo (grupo de restantes especies)
Buteo (grupo Leucopternis 2)
Lo que no es claro es donde irían Leucopternis princeps, plumbeus, schistaceus y lacernulata, pero por lo que se ve en el árbol, deberían ir antes de Rupornis, probablemente como un género aparte.
Additional comments from Remsen: In response to Manuel’s point above, I will be submitting a separate proposal on Leucopternis and Rupornis as soon as Fabio Raposo’s data are published. I think that it is important to deal with these issues one at a time, especially since to maintain Geranoaetus is contrary to all published data.”
Comments from Cadena: “NO, tentatively. I am on the fence with this proposal. Clearly, the phylogenetic studies mandate some taxonomic changes and merging Geranoaetus into Buteo makes some sense, but I wonder if a catch-all, highly heterogeneous Buteo is the way to go. It seems that a possibility would be to treat Geranoaetus, B. albicaudatus and B. polyosoma/poecilochrous as one genus, some Leucopternis, Harpyhaliaetus and Buteogallus as another genus, and the remainder of Leucopternis, Asturina and Buteo as yet another genus. I am not necessarily in favor of what I just proposed; my point is that, like Manuel, I think that taking a broader approach to classify this group considering several of the problems together might be best. (Note: The reference in the proposal is missing one of the authors of the Lerner et al. paper).”
Comments from Stotz: “No. In looking at Lerner, Klaver and Mindell, it is clear that this subunit of Accipitridae is a huge mess. I am not convinced though that trying to maintain a big Buteo is the way to go. Leucopternis and Buteogallus are very polyphyletic with pieces all over the tree. If we put Geranoaetus into Buteo then we have to put "true" Leucopternis (the melanops group) in Buteo, as well as the White Hawk group. We haven't done either of those things, so I feel this is being sequenced wrong. Further, if melanops and company go into Buteo, there are several of "Leucopternis" that will need names (e.g. lacernulatus, princeps, and schistaceus). My feeling is that we can't bite off this single piece. We need to think about the whole complex and figure out which are the groups we want to recognize at a generic level. One possibility is two big genera (Buteo and Buteogallus), which would have in Buteogallus our current Buteogallus, Harpyhaliaetus and some of Leucopternis, and in Buteo our current Buteo plus Parabuteo, Geranoaetus, and some of Leucopternis. An alternate strategy might be to recognize smaller subgroups. Possible subgroups in Buteo include Rupornis, Parabuteo (including leucorrhous), Geranoaetus (including polyosoma and albicaudatus), possibly the White Hawk complex, and possibly Leucopternis (the melanops groups, plus or minus Asturina), depending on how far down you'd want to whittle Buteo.”
Comments from Jaramillo: “NO – I do think that a large and broad Buteo is not a good way to go. The various clades within the larger Buteo should be broken up to give genera that are more meaningful and informative. So really, I would prefer to merge the three closely related species (polyosoma, albicaudatus, melanoleucus) into Geranoaetus. Then later one can break up the rest of the larger Buteo as the data comes in.”