Proposal (1038) to South American Classification Committee

Merge Milvago and Phalcoboenus into Daptrius

Note: This proposal’s origin started with a query from Joel Cabezas Salazar about why SACC maintained Milvago and Phalcoboenus when Clements/eBird has merged them into Daptrius. I was aware of the Fuchs et al. papers (see our SACC Note below) but was not aware that Clements/eBird had already instituted this merger without the issue first being considered by SACC and NACC. Now I have also learned that WGAC also went ahead and merged these genera way back in 2022, and this was followed by Clements/eBird. I now have access to the WGAC deliberations, which have influenced some of the discussion below.

Effect on SACC: This would merge two long-recognized genera, Milvago Spix 1824 and Phalcoboenus d’Orbigny 1834, into Daptrius Vieillot 1816.

Background: Generic boundaries in the caracaras have always been fluid, with virtually every combination or mergers among Caracara (formerly Polyborus), Ibycter, Daptrius, Milvago, and Phalcoboenus. For example, see our SACC notes 2 and 3b as well as 7b, copied below, as well as the synonymies in Hellmayr and Conover (1949). However, to the best of my knowledge, Milvago and Phalcoboenus have been maintained since at least Peters (1931) and Hellmayr and Conover (1949) until the Clements merger.

Here are our current SACC Notes:

7b.Vuilleumier (1970) proposed that Milvago be merged into Polyborus (= Caracara), but genetic data (e.g., Griffiths et al. 2004) indicate that they are not particularly closely related. Fuchs et al. (2012) found that Milvago itself is not monophyletic, with chimachima sister to Daptrius and chimango sister to Phalcoboenus; they recommended transfer of chimango to Phalcoboenus. This was followed Del Hoyo & Collar (2014). SACC proposal did not pass to transfer Milvago chimango to Phalcoboenus. Dickinson & Remsen (2013) transferred Milvago and Phalcoboenus to Daptrius. Fuchs et al. (2015) merged Milvago, Ibycter, and Phalcoboenus into Daptrius without providing rationale. SACC proposal badly needed.

7c. Amadon & Brown (1968) proposed that the two species of Milvago be considered superspecies; Vuilleumier (1970), however, pointed out that their degree of sympatry negated this treatment; although he considered them closely related, he also pointed out that they differed in morphology and likely also in ecology. Fuchs et al. (2012) found that they are not sister species – see Note 7b.

SACC proposal 561 dealt with this issue in 2012. That proposal was to move chimango to Phalcoboenus based on Fuchs (2012) was unanimously defeated; see the comments therein, especially by Mark Pearman and Sergio Seipke, concerning various phenotypic similarities and differences among the species. The theme of the comments suggested that a new genus for chimango was the best way to express phylogenetic and phenotypic, but there being no such genus, SACC left Milvago as a paraphyletic taxon. As one can see from the comments, there was fair support for merging all into Daptrius as a solution, but visceral opposition to also including Ibycter, as done subsequently by Fuchs et al. (2015), but no further action was taken.

Previously, Griffiths’ (1994) analysis of syringeal morphology was consistent with Daptrius (minus Ibycter americanus), Milvago, and Phalcoboenus forming a clade:

Griffiths (1999) then combined syringeal data with about 1000 bp of cytochrome b genetic data to produce similar results, although M. chimango was missing from the genetic analysis. Griffiths et al. (2004) analysis of RAG-1 sequences produced a different but weakly supported typology but still found the three genera to form a strongly supported clade (but M. chimango still missing):

Fuchs et al. (2012) were the first to include M. chimango (thanks to two USNM samples), and both mtDNA and nDNA gene trees showed that chimango was sister to D. ater with reasonably strong support, e.g.:

I don’t see any reason to dispute their findings; they even have more than 1 individual of the critical taxa.

Discussion:

Concerning the surprise that Milvago is not monophyletic, I suspect that part of the reason for their traditional treatment as congeners is that base color of the juvenal plumage of chimachima is dark brown, much like the plumage of adult chimachima, to the point that confusion in the field is evidently possible. Somehow, I had it my head, perhaps from over-interpretation of what I had read, that this might even be a case of neotenic plumage retention. However, I now consider that unlikely: the plumage patterns of the two superficially similar plumages differ in many ways, as can be seen in the photographs from Macaulay below, and as mentioned in our Bolivia guide (Herzog et al. 2016):

Look at the differences in ventral and dorsal patterning, as well as differences in the facial area, especially with respect to how much the eye stands out. Below are severely cropped head shots of adults from photos in Macaulay: chimachima on left (from Risaralda by David Monroy Rengifo), chimango on right (from Santa Fe by Horacio Luna); one can interpret the similarities as subjective evidence for placement in same genus, or the differences as subjective evidence for placement in different genera). By the way, the iris color difference holds up in all the photos I examined:

So, in my opinion, the finding that chimango and chimachima are not sisters is not that surprising. One could also make an ex-post-facto case that a chimango + Phalcoboenus relationship makes more sense biogeographically (temperate zone), as does a chimachima + Daptrius ater relationship (tropical rivers); we (Herzog et al. 2016 Bolivia guide) noted that the latter’s primary calls are fairly similar.

Therefore, I see no better option for now than transferring chimachima to Daptrius. Note also the relative short branch lengths in the tree (subsequently used by Fuchs et al. 2015 to merge all taxa into Daptrius. So, Milvago chimachima would become Daptrius chimachima). This would retain Milvago chimango in a monotypic genus, solving the problem of non-monophyly of Milvago as well as not messing with traditional Phalcoboenus. However, the type species of Milvago is chimachima, and therefore unavailable for chimango, and therefore chimango must be transferred to Phalcoboenus or have a new genus named for it. In the absence of the latter, we have no choice but to include chimango in Phalcoboenus or merge all into Daptrius.

Fuchs et al. (2015) used the data in Fuchs et al. (2012) to merge Milvago and Phalcoboenus as well as Ibycter into Daptrius. WGAC retained distinctive Ibycter but did merge the other two into Daptrius. Certainly from the tree in Fuchs et al. (2012), one can see the rationale for merging Milvago and Phalcoboenus into Daptrius: note the short branch lengths and the slightly suboptimal support for the node that divides them into two groups.

I can see reasons for not wanting to further expand Daptrius. Note the phenotypic and ecological differences noted between Phalcoboenus and the rest as expressed qualitatively in SACC 561, in which a merger was rejected.

As I see it there are only three alternatives:

(1) Maintain status quo by retaining Milvago as a non-monophyletic taxon and hope that someday someone will describe a new genus for chimachima. This would mean a NO vote on the proposal. I personally view this as unsatisfactory for obvious reasons.

(2) Transfer chimachima to Daptrius and chimango to Phalcoboenus. This would retain Phalcoboenus but “contaminate” that group by inclusion of chimachima. This would also mean a NO vote on the proposal, and result in a new proposal, 1039x.

(3). Transfer Milvago and Phalcoboenus to Daptrius. This will generate a negative reaction from many who know these birds (but so would option 2). I regard it as the least unpalatable of the options. It acknowledges that many genera, including raptors, include distinctive groups within them, including for example Falco. Therefore, I somewhat reluctantly recommend a YES on #3.

Lit Cit (see SACC Bibliography for the rest):

FUCHS, J., J. A. JOHNSON, AND D. P. MINDELL. 2012. Molecular systematics of the caracaras and allies (Falconidae: Polyborinae) inferred from mitochondrial and nuclear sequence data. Ibis 154: 520–532.

FUCHS, J., J. A. JOHNSON, AND D. P. MINDELL. 2015. Rapid diversification of falcons (Aves: Falconidae) due to expansion of open habitats in the Late Miocene. Molecular Phylogenetics and Evolution 82: 166–182.

GRIFFITHS, C. S. 1994. Monophyly of the Falconiformes based on syringeal morphology. Auk 111: 787–805.

GRIFFITHS, C. S. 1999. Phylogeny of the Falconidae inferred from molecular and morphological data. Auk 116: 116–130.

GRIFFITHS, C. S., G. F. BARROWCLOUGH, J. G. GROTH, AND L. MERTZ. 2004. Phylogeny of the Falconidae (Aves): a comparison of the efficacy of morphological, mitochondrial, and nuclear data. Molecular Phylogenetics and Evolution 32: 101–109.

Van Remsen, December 2024

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Vote tracking chart: https://www.museum.lsu.edu/~Remsen/SACCPropChart968-1043.htm

Comments from Robbins: “YES (option 3). I understand why some might not want to merge Milvago and Phalcoboenus into Daptrius, but I think the proposal’s explanation of why this is the best option is sound. Thus, I vote for option 3.”

Comments from Lane: “NO. I vote for 2. I really dislike the idea of collapsing everything into Daptrius, as I just don’t see the whole group fitting well into a single genus. I would prefer putting chimachima into Daptrius (both are “warm-country,” lowland river-edge spp) and chimango into Phalcoboenus (all are “cold country” spp, and chimachima is basically a neotenic Phalcoboenus in plumage). I know chimachima only from a few observations, so I don’t have a strong a feel for the beast in life but given that it is the most northerly lowlander in the “Phalcoboenus clade,” I can accept its smaller, more delicate structure as still representing that group as per Bergmann's Rule.” 

Comments from Zimmer: “NO. To borrow Van’s phrasing, I am going to have to vote for the “least unpalatable of the options”, which, for me, is Option 2, following Dan’s reasoning, and, with the hope that someone will come along and erect a monotypic genus for chimango, so that we can then restore the cohesiveness of Phalcoboenus.”

Comments from Areta: “NO. Here we are again on this... If we only had already described that new genus for chimango, I would go for it. I often regret that the explosion of phylogenetic information has not been accompanied by equally detailed phenotypic studies (of course: it takes more time to understand the birds than to produce phylogenetic trees) and taxonomic works (of course: high-impact journals mostly do not care about this). This is one of such cases. This, in the context of a global movement to have fewer genera at the expense of smaller neat groupings, has resulted in an all-encompassing Daptrius that is not very useful for communication. The fact that all species in the clade at stake are recently diverged adds another layer of complexity. I would love to have one genus for americanus (Ibycter), one for ater (Daptrius), one for chimachima (Milvago), one for chimango (undescribed), and one for the Andean-Patagonian caracaras (Phalcoboenus). This 5-genera treatment is not in the proposal, and, given the recent generic-lumping move, I doubt that it will gain much traction, unless thoroughly justified.

“I do not like it when the pressure to change generic limits because of new phylogenetic information leads to rapid assessments. Sometimes the taxonomic-nomenclatural matters need time to be sorted, and creating ephemeral new combinations strictly on phylogenetic data should not be recommended. But we are here, in this century in which waiting does not seem like an option. Meanwhile, the literature will be filled with Daptriuses until someone contests the broad Daptrius. Thus, given all this, and also voting for the least unpalatable of the currently available options in the proposals, I vote for option B: Daptrius ater and Daptrius chimachima, and Phalcoboenus chimango + the four traditional Phalcoboenus (and of course, retaining Ibycter americanus). Meanwhile, I´ll try to get to describe a new genus for our beloved chimango or tiuque.”

Comments from Niels Krabbe (voting for Del-Rio): “NO. After reading the earlier comments, I vote yes for option 2 (transfer chimachima to Daptrius and chimango to Phalcoboenus) and await Nacho's description of a new genus for chimango and a following new proposal.”

Comments from Fabio Raposo (voting for Bonaccorso): “NO. I vote for option 2, and I agree with Dan Lane's points regarding ecological segregation. It is important to note the short length of some branches, and genomic-era datasets may help us understand the stability and strength of the relationship between M. chimango and the Phalcoboenus clade.”