Proposal (514) to South American Classification Committee
Recognize Turdus sanchezorum
O’Neill et al. (2011) described Turdus sanchezorum (Varzea Thrush) from western Amazonia. The taxon was present in several museum collections but had been identified as T. hauxwelli in nearly all of them, as well as in studies including that species by Hellmayr (1938), Gyldenstolpe (1945a, 1945b, 1951), and Snow (1985). Vocal, morphological, and molecular data all conclusively showed that this new taxon was in fact the western Amazonian representative of the T. nudigenis clade, and was not at all closely related to T. hauxwelli or T. fumigatus (the sister to hauxwelli).
The molecular analysis presented in O’Neill et al. (2011) was a Bayesian phylogenetic hypothesis including T. sanchezorum and its closest relatives, based on 1035 base pairs of the ND2 gene. The results showed that the T. nudigenis clade (including T. rufiventris, T. maculirostris, T. grayi, T. nudigenis, T. sanchezorum, and T. haplochrous) was well supported, but within the clade, few relationships could be confidently resolved. The only relationships that were resolved were the sister relationship of T. rufiventris to the rest of the clade (not a surprise, as it is the most distinctive member morphologically and vocally), and the sister relationship between T. sanchezorum and T. haplochrous. This latter result could be used to place sanchezorum as a subspecies of haplochrous, but the two are as different from one another morphologically (mostly this refers to plumage pattern, as there was broad morphometric overlap in all members of the clade) as are any other clade members presently considered biological species by the SACC (e.g., see rationale in Proposal 385). Thus O’Neill et al. (2011) proposed the rank of species for T. sanchezorum.
Recommendation: Given the results of O’Neill et al.’s (2011) investigation, there is no question that T. sanchezorum is an overlooked member of the T. nudigenis clade in western Amazonia and, because there seems to be no previous name available, the name is therefore valid. The question is then whether to accept this taxon as a full species or not. I recommend that the SACC recognize it as a full species given the relative distinctiveness of sanchezorum with regard to haplochrous. Following the logic outlined in the description, the English name Varzea Thrush seems appropriate.
Gyldenstolpe, N. 1945a. The bird fauna of Rio Juruá in western Brazil. Kungliga Svenska Vetenskapakademiens Handlingar 22:1–338.
Gyldenstolpe, N. 1945b. A contribution to the ornithology of northern Bolivia. Kungliga Svenska Vetenskapakademiens Handlingar 23:1–300.
Gyldenstolpe, N. 1951. The ornithology of the Rio Purus region in western Brazil. Arkiv für Zoologi Serie 2, Band 2, 1:1–320.
Hellmayr, C. E. 1934. Catalogue of birds of the Americas. Field Museum of Natural History Zoological Series 13, part 7.
O’Neill, J.P., D. F. Lane, and L. N. Naka. 2011. A cryptic new species of thrush (Turdidae: Turdus) from western Amazonia. Condor 113:869–880. [pdf here: <http://cdc.lamolina.edu.pe/Noticias/Documentos/Condor2011_ONeill_etal.pdf>]
Snow, D. W. 1985. Systematics of the Turdus fumigatus/hauxwelli group of thrushes. Bulletin of the British Ornithologist’s Club 105:30–37.
Dan Lane, January 2012
Comments from Remsen: “YES. Having reviewed this paper in-house and talked with Dan about this extensively, I am convinced that sanchezorum is a valid taxon and that it should be ranked at the species level. (By the way, if anyone ever needs a good example of the importance of continued collecting of specimens, one could use this discovery as a nice example of how this cryptic species might have languished unrecognized indefinitely without modern specimens – see this paper’s Discussion.)”
Comments from Pérez: “A tentative YES. This is an amazing example of the need for continued collecting and exploration both for discovery and reevaluation of previous findings. No doubt we have a new taxon here, but the evidence does not seem to unconvincingly support species level rank for it (modest differences in morphology, vocal and molecular characters). However, species level differences among currently recognized Turdus species suggest T. sanchezorum should be considered a species until a thorough systematic and population level study is done for this group.”