Recognize Icterus pyrrhopterus as a separate species from Icterus cayanensis

 

Proposal (418) to South American Classification Committee

 

 

 

The southern populations of the Icterus cayanensis complex occur mostly south of the Amazon and comprise four named subspecies (pyrrhopterus, tibialis, periporphyrus, and valencio-buenoi). The four southern subspecies are here proposed to constitute a separate species, with the scientific name Icterus pyrrhopterus Vieillot 1819 (based on Azara No. 74), type locality Paraguay. The name pyrrhopterus has nomenclatural priority over the other three. The combination Icterus pyrrhopterus (or Xanthornus pyrrhopterus) has been widely used in the past, and well into the 20th century.

(A problem outside this proposal refers to the specific status of the two Amazonian populations Icterus cayanensis and I. chrysocephalus, regarded as conspecific in Blake [1966] and in SACC.)

 

Arguments for the species recognition of the southern pyrrhopterus populations include:

 

a) DNA data show the southern groups to be reciprocally monophyletic with the Amazonian groups, with no evidence of hybridization (D´Horta et al. 2008, Omland et al. 1999, Sturge et al. 2009).

 

b) Although in the map of D´Horta et al. (2008) nominate Amazonian form cayanensis and pyrrhopterus are shown as allopatric, field data from Beni, Bolivia, indicate local coexistence of both forms, at least during October-November (austral spring). Populations separated by only 4 km show characters of nominate cayanenis, or pyrrhopterus. No intermediate individuals are reported (data of B. Hennessey and S. Herzog, published in Jaramillo and Burke 1999).  This coexistence could be explained by northward seasonal movements of pyrrhopterus populations.  However, pyrrhopterus appears resident in Argentina at least as far south as Buenos Aires province (Narosky and Di Giacomo 1993).  Also, during the late austral winter (August-September), pairs or small groups of pyrrhopterus commonly visit blooming Tabebuia trees throughout northern Argentina and Paraguay (Fraga in press).  If some northward movement occurs, it should have ended by this time.

 

c) The southern group differs from both Amazonian forms cayanensis and chrysocephalus in being smaller in size, and having a more slender body shape and more acrobatic feeding habits (D´Horta et al. 2008, Fraga in press).

 

d) Habitat preferences for the southern pyrrhopterus group are broad and include forest and woodland edges (even in dry woodland), clearings, savannas, plantations, parks, gardens, and towns (D´Horta et al. 2008, Fraga in press.). Breeding occurs up to 1700 m in northwestern Argentina, probably higher up in Bolivia.  Populations of pyrrhopterus are usually abundant, and the species is currently expanding its range and numbers west and south in Argentina (Fraga in press).  The Amazonian groups chrysocephalus and cayanensis prefer palm groves of Mauritia flexuosa growing in swampy ground, or edges and canopy of humid forest (D´Horta et al. 2008). Both Amazonian forms are often described as local or uncommon (Hilty 2003).

 

Intraspecific variability within pyrrhopterus

 

D´ Horta et al. (2008) apply pure cladistic criteria and split pyrrhopterus and tibialis as two phylogenetic species (besides questioning the validity of the two other southern subspecies, a subject outside this proposal).  As to their main point, their analysis shows a huge area of intermediate specimens (estimated in 2,915, 400 km2) connecting tibialis and pyrrhopterus in eastern Brazil, making these two forms invalid species under the biological species concept.  Besides the huge intergrading zone, the habitat preferences of tibialis and pyrrhopterus are quite similar (D´Horta et al. 2008), and the same applies to nesting behavior (Fraga in press).

 

Proposed English name for Icterus pyrrhopterus

 

The proposed English name for Icterus pyrrhopterus is Variable Oriole.  The name makes reference to the considerable geographic variation in plumage. Individuals showing plumage variation may even occur far from the ranges of others subspecies, as observed by D´Horta et al. (2008).

 

References

 

Blake E. R. 1968. Family Icteridae. Pp. 138–202 in: Paynter R. A. Jr. (ed.) Check-list of birds of the World, vol. 14. Museum of Comparative Zoology, Cambridge, MA.

 

D´Horta, F. M., J. M. Cardoso da Silva, and C. C. Ribas. 2008. Species limits and hybridization zones in Icterus cayanensis–chrysocephalus group (Aves: Icteridae). Biological Journal of the Linnean Society 95: 583–597.

 

Fraga, R. M. in press (or 2011). Family Icteridae. In Handbook of the Birds of the World, Vol. 16. Lynx Edicions, Barcelona.

 

Hilty, S. 2003. Birds of Venezuela. Princeton Univ. Press. Princeton NJ.

 

Jaramillo, A., and P. Burke. 1999. New World blackbirds. The Icterids. A. & C. Black Publishers, London.

 

Narosky, T. and A. Di Giacomo. 1993. Las aves de la provincia de Buenos Aires, distribución y estatus. Vázquez Mazzini Editores, Buenos Aires.

 

Omland, K. E., S. M. Lanyon and S. J. Fritz. 1999. A molecular phylogeny of the New World orioles (Icterus): the importance of dense taxon sampling. Molecular Phylogenetics and Evolution 12:224-239.

 

Sturge, R., F. Jacobsen, B. B. Rosensteel, R. J. Neale and K. E. Omland. 2009. Colonization of South America from Caribbean Islands confirmed by molecular phylogeny with increased taxon sampling. Condor 11: 575-579.

 

 

Rosendo M. Fraga, October 2009

 

 

Comments from Zimmer: “YES.  Molecular evidence shows the two to be reciprocally monophyletic, they assortatively mate without evidence of hybridization in the narrow zone of overlap, and there are diagnosable morphological differences (both in plumage and biometrics).  The two populations are also known to differ ecologically.  The authors do not really address vocal differences, but in my experience, these are also pretty pronounced.”

 

Comments from Jaramillo: “YES.  I recall we implied that cayanensis was likely more closely related to chrysocephalus in our Icterid book. Apart from plumage and habitat differences, most compelling at the time at least in terms of separating cayanensis from pyrrhopterus was this area of possible sympatry in Bolivia. Now new information is available that clarifies that separating cayanensis and pyrrhopterus is a good course of action. An open question is what the relationship between cayanensis and chrysocephalus is.”

 

Comments from Robbins: “YES.  All the available data support the recognition of the southern pyrrhopterus as a species distinct from the Amazonian and northern forms.”

 

Comments from Stiles:  YES, for reasons well summarized by Fraga and other committee members.  As an aside, the pronounced geographic variation within pyrrhopterus should invite caution in splitting cayanensis and chrysocephalus without strong evidence suggesting reproductive isolation.”

 

Comments from Nores: “YES. Los análisis molecular de Omland et al. con dos diferentes vías (citocromo b y ND2)  muestran claramente que son dos especies diferentes. Importante también es que hay una zona de superposición sin hibridisación.”

 

Comments from Remsen:  “YES.  Although better resolution on potential contact areas is desirable, I’d say that available data places burden-of-proof on conspecificity.  I would note, however, that Chendo’s reason “d” is virtually irrelevant.  Widespread species tpyically have narrower habitat distributions where they occur in Amazonia (e.g., Vireo olivaceus).  Geographic variation in habitat preference and relative abundance is a widespread aspect of the biology of many species for which there is no indication that more than one species is involved.  I also worry about true sympatry (breeding) vs. seasonal sympatry due to movements by pyrrhopterus types.

 

Comments from Pacheco:  “YES.  Sou, igualmente, favorável à separação entre as populações amazônicas e cisa-amazônicas, sobretudo a partir das evidências moleculares acumuladas. A notória Intergradação entre as diferentes populações subordinadas à I. pyrrhopterus corrobora a sugestão de “Variable Oriole”