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 (C. ruficapillus and C. icterocephalus)
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 Arribá, 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behavioral comparison (unpublished data of R. Fraga) gives far more ambiguous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. Biología
y conservación (Xanthopsar flavus, Icteridae) en la Reserva
de Biosfera Bañados del Este. Documento de trabajo No. 29. PROBIDES, Rocha, Uruguay.
Fraga, R.
M., G. Pugnali and H. Casañas.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
________________________________________________________________________________________
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 género
separado. Pienso que el análisis 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."