Proposal (637) to South American Classification Committee

 

Treat Chloephaga melanoptera and Neochen jubata as congeners

 

The South American Sheldgeese (Chloephaga), which is essentially a group restricted to the southern cone, has never been a group that has been controversial. They all share a similar wing pattern and goose-like structure, although more closely related to shelducks (Tadorna). In contrast, the more northern Orinoco Goose (Neochen jubata) is very dark, tropical in distribution, has an entirely different wing pattern, and much iridescence in the plumage; its classification in a monotypic genus has never been controversial. Two other genera, from outside our region, have been considered to belong in this group based on morphological analyses: Cyanochen (Blue-winged Goose) and Alopochen (Egyptian Goose) (Livezey 1997). More recent work, using sequence data, has shown that Cyanochen is well outside this group and it is likely sister to Hartlaub’s Duck (Pteronetta hartlaubii).

 

New information: Bulgarella et al. (2014) published a complete phylogeny of Chloephaga based on molecular a dataset. They used sequence data from the mitochondrial DNA control region to look at divergence and relationships. No nuclear data were used in the analysis. Although the aim of the paper was to quantify genetic divergence among insular and mainland populations of Chloephaga geese, they found an unexpected result relating to Neochen. Their results show that Neochen and Andean Goose (Chloephaga melanoptera) are sister species, and the pair is sister to the rest of Chloephaga. Given the lack of nuclear gene sequence data, and the small sample size it is tempting to wait for another paper with a larger dataset to act on this single result. However, I think there are ample reasons to consider that this relationship between Neochen and C. melanoptera is not only supportable, but in hindsight seemingly obvious. 

 

Andean Goose was always the odd Chloephaga: The remaining four species of Chloephaga share the same wing pattern, a similar body shape, are strongly aquatic, nest on the ground, and are restricted to lowland temperate regions of the southern cone of the continent. The Andean Goose on the other hand has a different wing pattern in which the dark stripe on the wing does not extend from wing base to primaries. Also, Andean Goose shows white primary coverts contrasting with blackish primaries, whereas in other Chloephaga the greater primary coverts are dark, and the alula and lesser primary coverts are a mix of dark and white. The body shape of the Andean Goose is odd in that it holds its neck and nape inflated, giving it a strange head/neck shape. The tertials are broad and bulky, almost forming a bustle on the rear end that is missing from Chloephaga. Another difference is that the dark parts on the sitting bird, mainly on the rear, are iridescent, whereas on Chloephaga iridescence is restricted to the dark bar on the greater coverts. Rather than ground nesting, Andean Goose tends to nest on cliffs. Vocally it is divergent from Chloephaga, although the difference is not obvious without some attention to the details of the sound.

 

Structure and Plumage: Both the Andean Goose and the Orinoco Goose share the same odd puffed nape, and neck that is unlike Chloephaga. It is a difficult structural shape to describe because I think it is mainly created by the length of the feathers themselves and how they are held erect in most cases, but a quick look at various photos of the species involved shows them well. Both Andean and Orinoco geese can show the structural striping on the neck, as in the unrelated true goose genus Chen, but it is not something you see on true Chloephaga. Similarly, the broad tertials that form a bustle on the rear parts -- a feature shared with Neochen. Iridescence on the tertials as well as upperparts feathering is also shared by Orinoco and Andean geese and is quite different from that of Chloephaga. Both the Orinoco and Andean geese show substantial iridescence on the upperparts, including the tertials and lower scapulars and back feathers. This feature unites them and sets them apart from true Chloephaga.

 

Nesting and habitat: The Orinoco Goose is a tree-nesting species, although terrestrial when foraging. They will use a large cavity or broken-off snag as a nest-site. The Andean Goose often nests on cliffs overlooking the water, on a ledge or nook in the cliff. That these are the two species geese that are terrestrial but nest away from flat ground is something that unites the two and separates them from Chloephaga. All of these geese are terrestrial, sometimes foraging far from water. The most aquatic is the marine Kelp Goose, whereas the rest graze and are not necessarily found close to water. However, when closer to water, Chloephaga retreat to water when alarmed or with chicks. In contrast, in my experience Andean Geese retreat by flying or walking away, but do not tend to swim. In fact, of the hundreds if not thousands of Andean Geese I have observed, I do not recall them swimming. Similarly, Orinoco Goose is not a species that commonly swims, although I am much less experienced with that species.

 

Distribution: Both the Andean and Orinoco geese are found much farther north than core Chloephaga. In fact in range they replace each other, one in the highlands of the Andes, and the other in the lowland savannas east of the Andes. There is little overlap in the distribution of Andean Goose and Upland Goose, but essentially Andean and Orinoco are allopatric with the southern Chloephaga. All other Chloephaga are sympatric, separating out ecologically. Although most of the species are often found together, the strictly marine Kelp Goose stands out in being found within sight of the other species, but associating usually with the other species due to the habitat difference. 

 

Voice: This needs more study; all of these geese have male whistling calls and female grunting voices. Although in listening to voices on xeno-canto, to me the structure of sounds of Andean and Orinoco geese are more similar to each other than they are to Chloephaga.

 

Chicks: The plumage of downy young is an interesting character. It is particularly interesting given the different habitat and ecology of the species. Both Andean and Orinoco geese have brightly plumaged chicks, essentially black-and-white striped. They have white faces, black crowns and back of neck, and a black patch around the eye and black spot on the ear. Overall, they are remarkably similar.  Downy young of the southern Chloephaga are variable, bolder striped on Ruddy-headed Goose, but not nearly as contrasting as that of Andean-Orinoco, and not showing the black ear patch. Kelp Goose has greyish white chicks, Upland Goose also dull largely unicolored youngsters but a buff color. Here are some photos to compare:

 

Andean Goose https://www.flickr.com/photos/55681839@N07/7678638248/

Orinoco Goose https://www.superstock.com/stock-photos-images/4273-12414

 

Upland Goose http://ibc.lynxeds.com/photo/upland-goose-chloephaga-picta/pair-three-small-chicks-swimming

 

Ruddy-headed Goose http://www.surfbirds.com/community-blogs/falklandbirder/2008/11/

 

Recommendation: I think that the evidence is strong that Andean and Orinoco geese are sister species, and that these are sister to Chloephaga, although somewhat distantly related. This creates a polyphyletic Chloephaga, and there are two options: either include Orinoco Goose in Chloephaga (which has priority over Neochen), or include Andean Goose in Neochen. I recommend moving Andean Goose to Neochen because this creates genera that are more succinct and easier to define than to expand Chloephaga.

 

Literature Cited

Bulgarella, M., Sorenson, M. D., Peters, J. L., Wilson, R. E. and McCracken, K. G. (2010). Phylogenetic relationships of Amazonetta, Speculanas, Lophonetta, and Tachyeres: four morphologically divergent duck genera endemic to South America. J. Avian Biol. 41: 186–199.

 

BULGARELLA, M., C KOPUCHIAN, A. S. DI GIACOMO, R. MATUS, O. BLANK, R. E. WILSON, AND K. G. MCCRACKEN.  2014.  Molecular phylogeny of the South American sheldgeese with implications for conservation of Falkland Islands (Malvinas) and continental populations of the Ruddy-headed Goose Chloephaga rubidiceps and Upland Goose C. picta.  Bird Conservation International 24: 59-71.

 

LIVEZEY, B. C. 1997. A phylogenetic classification of waterfowl (Aves: Anseriformes), including selected fossil species. Annals Carnegie Museum 66: 457-496.

 

Alvaro Jaramillo, July 2014

 

 

Note from Vitor Piacentini: The Andean Goose ("Chloephaga" melanoptera) is the type species [by monotypy] of Oressochen Bannister, 1870, whereas the Orinoco Goose is the type of Neochen Oberholser, 1918.  It is thus clear that, if both species are to be treated in a single genus of their own, the valid name of such genus is Oressochen.

 

Further, as clarified by Normand David at http://www.zoonomen.net/avtax/n/c.html#C.canagicaSpell, the final component chen is the transliterated Greek noun Xen (= goose), which may be either masculine or feminine.  In the original description of Oressochen, Bannister, treated it as masculine (see http://biodiversitylibrary.org/page/26300502), so the valid names of the Andean and the Orinoco geese would become, respectively, Oressochen melanopterus (Eyton) and Oressochen jubatus (Spix).

 

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Comments from Zimmer: “YES”.  Alvaro does a nice job of summarizing the diverse characters that unite C. melanoptera with N. jubata.  Collectively, these are more convincing to me than the mitochondrial DNA data, although the two data sets are concordant in pointing to the stronger sister relationship between these two species relative to the rest of Chloephaga.  The way to deal with a polyphyletic Chloephaga is largely a matter of taste (expand Chloephaga to include Neochen, or transfer C. melanoptera to Neochen), and in such cases, I usually prefer to come down on the side of more narrowly defined, internally cohesive genera, so that’s how I’m voting here.”

 

Comments from Robbins: “YES, Alvaro’s assessment combined with the genetic data are convincing that melanoptera and jubata are sister taxa. What genus to place these is subjective.”

 

Comments from Stiles: “YES, the genetics clearly indicate the sisterhood of melanoptera and jubata and like Kevin, I favor diagnosable genera wherever such a choice could go either way, hence I favor transferring the former to Neochen.

 

Comments from Remsen: “YES, but reluctantly.  The genetic data are strictly mtDNA data, and so caution should be exercised concerning potential species tree/gene tree problems. Nonetheless, transfer of Chloephaga melanoptera into Neochen seems warranted even on morphological etc. grounds, for reasons outlined by Alvaro.  I was unaware of all the jubata- melanoptera similarities vs. other Chloephaga – nice work, Alvaro.”

 

Comments from Stotz: “YES.  Well-reasoned proposal by Alvaro.”

 

Note from Remsen: All comments above written before Vitor’s comment inserted, so names need to be adjusted accordingly.

 

Comment from Piacentini: “SACC members implicitly discussed whether to treat all Chloephaga+Neochen in a single genus (Chloephaga would have priority) or to move C. melanoptera to Neochen.  A third option that should have been considered is to treat the Andean Goose in its own, monotypic genus, sister to Neochen.  Alvaro greatly summarized the similarities between Andean and Orinoco geese.  What about the differences between them?  Aren't these differences greater then the differences between the true Chloephaga's and either the Andean or the Orinoco goose? If this third option were considered, would the proposal have another result?”

 

Comments from Pacheco: “YES, following Vitor and accepting the combinations Oressochen melanopterus and Oressochen jubatus (Spix); a more restrictive genus now seems more appropriate.”