Proposal (78) to South American Classification Committee

 

Proposal for keeping the monotypic genus Xanthopsar Ridgway 1901

 

With the new molecular phylogeny of the Icteridae (Johnson and Lanyon 1999) there is no chance of putting Xanthopsar flavus within the Nearctic and Caribbean genus Agelaius. The most recent phylogenetic tree places Xanthopsar in a basal position within a clade of five species, two in the genus Chrysomus Swainson (Cruficapillus and Cicterocephalus) and two in the genus Pseudoleistes Sclater (P.guirahuro and P. virescens). There are four alternatives: a) putting Xanthopsar flavus within the genus Chrysomus b) putting Xanthopsar flavus within the genus Pseudoleistes and c) leaving this species in a monotypic genus. The fourth alternative, putting all the five species in the clade in one genus (Chrysomus has priority over Pseudoleistes) seems unconvincing. The combination Chrysomus flavus has been sometimes used (e.g. by the Argentinian naturalist Lynch Arrib‡, but Pseudoleistes flavus not, as far a as I know. Alternative a) would make Pseudoleistes not monophyletic, but b) and c) have no problems.

 

Externally Xanthopsar flavus resembles the Chrysomus blackbirds mostly in size and in the marked sexual dimorphism in coloration. Notice, however, that the female Xanthopsar is more brightly colored than any Chrysomus. The Pseudoleistes are large and monomorphic. Skeletal characters analyzed by Webster (2003) indicate a closer resemblance between Xanthopsar and the South American marsh blackbirds (Chrysomus in the wide sense). However, in his Principal Component Analysis, and in some individual characters (stoutness of the tarsometatarsus) Xanthopsar was somewhat distant to those species. There was no skeletal resemblance to Pseudoleistes, but the effects of size on skeletal characters (allometry) were not researched.

 

A behavioral comparison (unpublished data of R. Fraga) gives far more ambiguous results. The song of Xanthopsar flavus, brief, strident and variable, may sound vaguely similar to the "buzzing" songs of Chrysomus. In sonograms, there is just a minimal resemblance. The buzzing songs of Chrysomus consist of a short introduction plus a long, rather stereotyped, nasal note. However, the two Chrysomus have two song types ("buzzing" and "musical", often alternated) and Xanthopsar flavus just one. The musical songs, particularly in ruficapillus, are long and complex, unlike anything in Xanthopsar. Unlike the Chrysomus, the female sings in Xanthopsar flavus, and the song is similar to that of the male. The vocalizations of both Pseudoleistes are divergent and complex, particularly in virescens; this may reflect the complex social organization and cooperative habits of those species. In P. guirahuro putative males produce short songs while nesting, and these include a final buzzing note (with a vague resemblance to Chrysomus).

 

Preliminary information suggests a clear resemblance between the begging calls of chicks of Xanthopsar, both Pseudoleistes and some Chrysomus. The male sexual displays of Xanthopsar flavus do not include typical Song Spread postures, as in Chrysomus. Courting Xanthopsar flavus males often display the bright rump patch, as in Pseudoleistes guirahuro (but the other species in this comparison lack rump patches).

 

The feeding ecology of Xanthopsar flavus closely resembles that of both Pseudoleistes, as it feeds mostly on arthropods obtained by probing or gaping the topsoil (Azpiroz 2000, Fraga et al 1998). The habit of feeding on humid grasslands, and not in the water, is another point in common.

 

The breeding biology of Xanthopsar flavus again resembles the two Pseudoleistes. The males do not build the nest, but otherwise defend the nest, and feed the female and chicks (Fraga et al. 1998). Monogamy seems the rule, and helpers at the nest may occur (Azpiroz and pers. obs.). The two Chrysomus blackbirds are often polygynous; male parental care includes building the nest (very unusual in the Icteridae), but chick feeding is mostly by the female. Helpers have not been reported in any species of Chrysomus.

 

To summarize, I think the information favors alternative c), keeping Xanthopsar flavus in a monotypic genus. It is, however, somewhat intermediate between Chrysomus and Pseudoleistes, perhaps closer to a form ancestral to all the group.

 

Azpiroz, A. B. 2000. Biolog’a y conservaci—n (Xanthopsar flavus, Icteridae) en la Reserva de Biosfera Ba–ados del Este. Documento de trabajo No. 29. PROBIDES, Rocha, Uruguay.

Fraga, R. M., G. Pugnali and H. Casa–as.1998. Natural history and conservation status of the endangered Saffron-cowled Blackbird Xanthopsar flavus in Argentina. Bird Conservation International 8:255-267.

Johnson, K. P., and S. M. Lanyon. 1999. Molecular systematics of the grackles and allies, and the effect of additional sequence (CYT Band ND2). Auk 116:759-768.

Webster, J. D. 2003. Skeletal characters and the genera of blackbirds (Icteridae). Condor 105:239-257.

 

Rosendo M. Fraga, November 2003

 

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Comments from Stiles: "YES. As I understand it, retaining Xanthopsar does represent maintaining the status quo, and Fraga's arguments seem reasonably convincing."

 

Comments from Zimmer: "YES. I can't see this species as a Pseudoleistes. The two species currently recognized as such form a distinctive pair, structurally, vocally, ecologically and in plumage characters. Xanthopsar is similar in foraging behavior to P. guirahuro (with which it commonly feeds side-by-side) and habitat, but seems divergent in most other respects. It also doesn't seem a good fit with Chrysomus, especially when you consider female plumage patterns and ecology. Retention of the monotypic genus seems to me the best course."

 

Comments from Stotz: "YES. Although I am generally not inclined toward monotypic genera, this one stands out from the others, and won't make Chrysomus polyphyletic. I am also a bit concerned that we might be a little ahead of the data curve on blackbird genera."

 

Comments from Jaramillo: "YES. Lumping this genus into Pseudoleistes, which is the clear alternative in my mind, makes little sense. It would make a heterogeneous genus that is much less informative than retaining the two entities as they are."

 

Comments from Nores: "Yes. Acepto mantener Xanthopsar como un gˇnero separado. Pienso que el an‡lisis de Rosendo es concluyente, lo cual coincide con lo mi experiencia personal sobre estas especies."

 

Comments from Robbins: " A reluctant "Yes". I'm not convinced this is the best course of action, but given what information we do have it seems the most conservative solution."