There is no described geographic variation.
There is no described geographic variation.
Remsen et al. (2009): Passeriformes: Thraupidae: Nephelornis oneilli Lowery and Tallman
The initially uncertain status of the Pardusco's (Nephelornis oneilli) systematics mirrored the habitat preference from which its generic name is derived: nephele (cloud) = "bird of clouds or mist" (Lowery and Tallman 1976: 424). While clearly a New World nine-primaried oscine, Lowery and Tallman could not determine its membership within any subdivision of that group, in part due to the lack of clear diagnostic characters in external morphology or behavior defining such subdivisions. Their conclusion was: "of uncertain affinities" (Lowery and Tallman 1976: 415).
Sufficient specimens were collected and prepared in diverse manners (skins, skeletons, alcoholics), thereby enabling Walter J. Bock to examine tongue myology and skeletal characters. Within Lowery and Tallman (1976), Bock reported two significant tongue muscle characters and from those concluded that Nephelornis is a basal branch of the New World nine-primaried oscines. The authors ultimately recommended it be listed next to Conirostrum among the genera incertae sedis that follow the Parulidae in Lowery and Monroe (1968). Interestingly, Lowery and Tallman (1976: 427) did foreshadow its ultimate classification when they stated "[C]onceivably Nephelornis might be relegated to the Thraupinae". They hoped that the use of molecular characters would resolve its placement.
Raikow (1978), studying appendicular myology in a broad suite of oscines, found that Nephelornis shares five similarities with parulids, five with emberizids, and seven with thraupids (he eschewed the Paynter and Storer group rankings for these nine-primaried oscines that appeared in Paynter 1970). He concluded that the genus is closest to Urothraupis based on being nearly indistinguishable in terms of hindlimb musculature. However, the unexplained movement of Urothraupis from thraupids to Emberizinae by Paynter (1970), the re-ranking of Thraupidae to Thraupinae by Paynter (1970), and the similarities with two other New World nine-primaried oscine groups caused Raikow to be conservative and assign Nephelornis and Urothraupis to the base of the thraupine-emberizine assemblage. Ultimately, he recommended restoration of Urothraupis to a family-ranked Thraupidae and placement next to Nephelornis, with both being near the base of the family.
The placement of Nephelornis as a tanager was not yet clear, nor was the classification of the New World nine-primaried oscines stable. Parker et al. (1982) placed the taxon in the family Coerebidae instead of Thraupidae and named it O'Neill's Pardusco based on the specific epithet from the type description that honored the great contributions to Peruvian ornithology made by John P. O'Neill. Interestingly, the senior author (Theodore H. Parker III) had collected the holotype.
The first analyses involving Nephelornis using molecular characters were based on DNA-DNA hybridization. Sibley and Ahlquist (1985) produced a diagram that placed Nephelornis with other tanagers, but they cautioned that the results did not provide a phylogeny. Bledsoe (1985, 1987) and Bledsoe and Sheldon (1989) involved Nephelornis in their studies, and it fell among some tanagers; however, establishing a phylogeny was not an objective of these papers. Bledsoe (1988) did place it in a tanager clade including Tersina and Catamblyrhynchus. Sibley and Ahlquist (1990) followed with their placement of Nephelornis within the tanager clade (tribe Thraupini within subfamily Emerizinae in their new classification).
Although there was an extensive shift to using molecular characters in avian systematics, Webster (1988, 1992) analyzed skeletal features of tanagers including this genus. However, he did not propose a phylogeny.
Although the DNA-DNA hybridization studies suffered from a lack of taxa, the placement of Nephelornis within the tanagers (albeit an aberrant one) became more-or-less accepted in the critical works of Isler and Isler (1987), Ridgely and Tudor (1989) and Fjeldså and Krabbe (1990). Sister taxon relationships remained uncertain since its initial placement next to Conirostrum, supplanted by Urothraupis; this was also due to the paucity of comparison to a wide array of taxa.
The solidification of Nephelornis as a tanager and insight into its tanager clade came with the study of Burns (1997). He corrected the deficit of taxa by doing the most comprehensive survey of tanagers using a molecular method: mitochondrial DNA (mtDNA; specifically, cytochrome b gene sequence). Burns (1997: 345) placed the genus within the clade "Hemispingus and relatives" (Hemispingus, Nephelornis, Cnemoscopus, Pyrrhocoma, Thlypopsis, and Cypsnagra). Most members of this clade have nondescript plumage and are Andean in distribution. Cypsnagra now becomes the likely sister taxon.
Other mtDNA studies have used Nephelornis as a tanager in examining other groups (Burns et al. 2002, Burns et al. 2003, Yuri and Mindell 2002), but they did not address Nephelornis systematics.
Lougheed et al. (2000) studied 12 species of warbling finches (Emberizinae: Poospiza) and all species studied by Burns (1997) using the mtDNA cytochrome b gene; note their misspelling of the specific epithet of pardusco as "oniellei" throughout. They found that not only do many Poospiza species fall within the Hemispingus and relatives clade of Burns (1997), but that Nephelornis is basal to a clade containing P. erythrophrys, P. alticola, P. torquata and P. melanoleuca.
Finally, Jonsson and Fjeldså (2006) produced an oscine supertree from 99 source phylogenies using molecular characters. Their supertree recovered the Hemispingus and relatives clade of Burns (1997) with the addition of many Poospiza species (Lougheed et al. 2000), although not with all of the same relationships within the clade. Their supertree places Nephelornis and Cypsnagra as sister taxa, followed by Pyrrhocoma and Thlypopsis sordida; Poospiza is more distantly related.
Contemporary field guides treat Nephelornis oneilli as a tanager (Clements and Shany 2001, Schulenberg et al. 2007). The best expression of its current status is that the Pardusco is an odd, disparate Andean tanager (Schulenberg et al. 2007: 578) within the Hemispingus and relatives clade (Burns 1997) which now includes some of the Poospiza species (Lougheed et al. 2000). Its definitive sister taxon is yet to be resolved.
The first specimens of the Pardusco were collected by Reyes Rivera and another Peruvian field assistant during an expedition led by John P. O'Neill to the Acomayo area of the Departamento de Huanuco (Stap 1990). Although the species was known to these Peruvian locals, O'Neill recognized that this was new to science and that the discovery was dramatic due to its uncertain familial membership. Additionally, it was considered to be a surprising find as previous field work had occured in the general area by Zimmer (1930) and other Louisiana State University Museum of Zoology expeditions (Lowery and Tallman 1976). It was one of only two new genera found during the five year period of 1976-1980 and therefore one of the two most noteworthy bird discoveries (Vuilleumier and Mayr 1987).
While new species of birds since the second half of the twentieth century tend to be small-bodied, it is more likely that conspicuousness determines their likelihood for discovery (Gaston and Blackburn 1994). Part of conspicuousness involves habitat specificity which illustrates the need to thoroughly work all habitats and elevations in the ecologically and topographically diverse Andes. The lesson of discovery of this new genus less than 50 years ago still rings true today (Lowery and Tallman 1976: 416): "One can only speculate how many more ornithological treasure-troves await discovery in the rugged massifs of the Peruvian Andes."