Proposal (356) to South American Classification Committee
Treat Anas andium as a separate species from Anas flavirostris
Effect on South American Checklist: This proposal would add a species to the Main List by elevating the andium subspecies group to species rank.
Background: Our current Note is as follows:
18. The subspecies andium was considered a separate species from Anas flavirostris by Ridgely et al. (2001), as they were treated by Hellmayr & Conover (1948a), based on differences in bill and plumage color; followed by Hilty (2003). Proposal needed. Jaramillo (2003) further suggested that the subspecies oxyptera may also deserve recognition as a separate species from A. flavirostris.
I do not have any first-hand knowledge of the taxa involved, nor am I aware of recent data that address the problem directly, but given the disparity in ranking of andium in recent treatments, I think we have to address this with a proposal.
Our current A. flavirostris includes the nominate form, which is widespread in lowland southern South America, and three subspecies found in the Andes from Venezuela and Colombia to n. Chile and n. Argentina. The nominate form and the southernmost Andean subspecies, oxyptera, share a mostly yellow bill, whereas the two other Andean subspecies, andium and altipetens, have an all dark bill. The break between yellow-billed and dark-billed birds is evidently at the Mara–on. Therefore, they are narrowly allopatric with no known contact zone. Therefore, we have the usual problem of how to treat allopatric taxa.
The primary difference between the two groups is bill color, although there are other plumage differences between the groups and among the subspecies. Schulenberg et al. (2007) illustrate oxyptera and andium, with andium shown with a substantially paler head. Jaramillo (2003) shows both oxyptera and nominate flavirostris, with oxyptera clearly much paler ventrally. Hilty (2003) shows northernmost altipetens, which differs from andium in having a less bronzy speculum, paler dorsal plumage, and less heavily marked head (Hellmayr and Conover 1948, Blake 1977).
Johnsgard (1978, 1979) treated them as conspecific, so that implies (to me) that at least at that time there were no known behavioral/display/vocal differences between the two groups, nor are any differences referenced in HBW (Carboneras 1992f).
Johnson & Sorenson (1999) included samples of nominate flavirostris and oxyptera in their mtDNA analysis and found them to be identical; unfortunately, no andium were available.
Analysis: In the absence of any data on gene flow, we are left to assign species rank based on comparative analysis. Because both treatments have wide acceptance in the literature, I do not think that we have to demand strong data to change from our current classification.
With little conviction, I recommend a YES vote on the split on the following basis. First, I cannot think of a case of two taxa of ducks known to interbreed freely that have such different bill colors. [Please correct me if wrong.] We currently treat A. puna as a separate species from A. versicolor, and the primary difference between them is bill color (one lacks yellow). Second, the two bill color types come reasonably close to each other without any sign of current or past gene flow. I doubt that the Mara–on is much of a barrier to a teal. If there were a low frequency of opposite bill colors in the populations closest to one another, then I would take that as evidence of gene flow. A yellow-billed individual has been seen in Ecuador (Ridgely & Greenfield 1001), but its provenance cannot be known. Third, as far as I know, an explicit rationale for their treatment as a single species has not been published (although I have not checked the Delacour literature).
Note: if the proposal passes, Ridgely & Greenfield (2001) used Andean Teal for andium, and I see no reason not to follow that. However, they used Speckled Teal for nominate + oxyptera rather than using a separate name to distinguish narrow vs. broad definitions of flavirostris. Madge and Burn (1988, "Waterfowl") used Yellow-billed Teal for narrowly defined flavirostris, and this makes more sense to me, because it prevents confusion.
Van Remsen, May 2008
Comments from Stiles: "YES although, like Van, without a strong commitment to this. The clear-cut and definite difference in bill color with no suggestion of intermediates despite close geographical approach in N Peru suggests that allospecies status might be most appropriate. I also note that the morphometric data of Blake (1977, Manual of Neotropical Birds) suggests this: there is a tendency towards increasing size from altipetens to andium albeit with much overlap; however, oxyptera (the form adjacent to andium) is considerably smaller (little or no overlap in wing and bill measurements). This said, it is also worth noting that nominate flavirostris is also much smaller than oxyptera and differs in plumage coloration to a comparable degree, although sharing the yellow bill. It is also more of a lowland bird (exclusively?) and (if I read Blake correctly) breeds much further south and is the only migratory form of the group, migrating N from its far southern breeding grounds (does it overlap in winter with oxyptera?). I know of no detailed studies of voice or behavior in this group. For the moment, it seems reasonable to split andium (Andean Teal) from flavirostris (Yellow-billed Teal), but at some point, the status of oxyptera vs. flavirostris should be addressed in detail as well."
Comments from Robbins: "YES, I'm fine with elevating the two different bill color taxa to species, but I doubt if bill color would have any influence on assorted mating given that sister taxa of other ducks, e.g., cyanoptera x discors, which have dramatic plumage differences interbreed. Having said that, even if they would interbreed shouldn't have much bearing on their taxonomy. What is needed are comparative genetic data between dark and yellow billed forms to help us gauge how much differentiation has occurred in this group."
Comments from Nores: "YES, pero con poco convencimiento. Como lo ha manifestado Remsen parece que no hay subespecies de patos con diferente color de pico."
Comments from Zimmer: "YES, for reasons nicely summarized by Van. The differences in these birds go beyond the striking bill color differences - plumage is more different than you might think from looking at illustrations. For now, I would say keep oxyptera and flavirostris together, but with the awareness that those two might prove to be separate at some point. I would also support the English name of "Andean Teal" for the dark-billed populations, and "Yellow-billed Teal" for flavirostris/oxyptera."
Comments from Stotz: "YES. I would favor Yellow-billed Teal for flavirostris."
Comments from Jaramillo: "YES - There are bill color, plumage, size differences that set these two taxa apart. I also recall seeing a paper by Kevin McCracken at an AOU meeting (St. Louis perhaps?) that showed a phylogeny where the three members of the flavirostris complex actually were rather distinct genetically. As far as I know, this is not published, and I have no recollection of the methodology. The oxyptera versus flavirostris issue is better left for another proposal and perhaps some publication. The two forms are now more and more found in the same flocks, even in the breeding period (Mendoza, Argentina; highlands of Santiago, Chile; highlands of Salta, Argentina). As breeders the two are nearly sympatric, and no intermediates are known. Like andium, these two forms are actually much more readily separable than some illustrations would lead you to believe."
Comments from Schulenberg: "YES. I'm not wild about the English name "Yellow-billed" Teal, in view of the extensive geographic overlap with of this species with Yellow-billed Pintail. If we wanted to stick with convention, then the main contenders are "Yellow-billed" (which matches the specific epithet; dates back at least to Phillips 1923, also was used by Hellmayr and Conover 1948) or "Chilean" (used by Delacour 195x-196x, also Scott 1961). I can't imagine that the name "Chilean" would be very popular in Argentina, much less Bolivia or Peru. But I still worry about flubs, at least in the field, when using Yellow-billed Pintail and Yellow-billed Teal. Is anyone else worried about this? Should we rack our brains for a better suggestions, or just give in the easy route ("Yellow-billed")?"
Comments from Pacheco: "YES. Em vista do aqui apresentado, eu voto "sim". Cabe lembrar que um dicromatismo sexual na colora¨‹o do bico ˇ conhecido.
Wilson, R. E., S. D. Goldfeder, and K. G. McCracken (2004) Bill sexual dichromatism of Yellow-billed Pintail (Anas georgica) and Speckled Teal (A. flavirostris). Ornitologia Neotropical 15:543-545."