Arremon polionotus Bonaparte, 1850

Buainain, Nelson, Brito, Guilherme Renzo Rocha, Firme, Daniel Honorato, Figueira, Daniel Monteiro, Raposo, Marcos A. & Assis, Claydson Pinto De, 2016, Taxonomic revision of Saffron-billed Sparrow Arremon flavirostris Swainson, 1838 (Aves: Passerellidae) with comments on its holotype and type locality, Zootaxa 4178 (4), pp. 547-567 : 561-562

Arremon polionotus Bonaparte, 1850

Arremon devillii Des Murs, 1856 : pp. 69

Arremon callistus Oberholser, 1901 : pp. 188 ( Hellmayr 1906: pp. 311) Arremon polionotus devillii Des Murs, 1856 : pp. 69 ( Hellmayr 1906: pp. 312) Arremon flavirostris polionotus Bonaparte, 1850 : pp. 487 ( Hartert & Venturi 1909: pp. 172) Arremon flavirostris devillii Des Murs, 1856 : pp. 69 ( Hellmayr 1938: pp. 430)

Holotype. MNHNP 7029 (Museu National d’Histoire Naturelle, Paris), adult male, “ Corrientes ”.

Type locality. Corrientes, Argentina (original designation).

Plumage diagnosis. Differs from A. dorbignii by short white superciliary stripes starting above eye instead of right after the bill; Medium Neutral Gray (color 84 in Smithe 1975) crown stripe absent or restricted to a few feathers between the nape and bill in adults, instead of always present and starting at bill insertion. It differs from A. dorbignii and A. flavirostris by its dorsal regions (including scapulars and tail-coverts) being variable in tone (78/ 79/84) instead of Yellowish Olive-Green (50); plain Sepia (119) rectrices with no Yellowish Olive-Green (50).

Description. Conical bill; mandible Orange Yellow (18); maxilla Orange Yellow (18) with black ridge starting at base of bill at level of nares, becoming thinner as it reaches tip; black head and auriculars; Medium Neutral Gray (84) crown stripe may be present or absent, starting somewhere between bill insertion and nape; bold white superciliary stripes starting above eye and reaching sides of nape; nape Medium Neutral Gray (84); rest of dorsal regions (including scapulars and tail-coverts) Plumbeous Gray (78); wing-coverts Yellowish Olive-Green (50); edge of marginal wing-coverts Spectrum Yellow (55); remiges and rectrices Sepia (119); white ventral regions (chin, chest, breast and abdomen) contrasting with black pectoral band; Light Neutral Gray (85) sides and flanks, thighs white with Glaucous (79).

Sexual dimorphism. Females have plumage generally tinged Buff (24), more visible on ventral regions, but also subtly on superciliary and crown stripes, the latter being more evident than in adult males. On dorsal regions buff tones vary between Glaucous (79) and Olive (30).

Immature. Younger immature has Black bill; Greenish Olive (49) dorsal regions and sides, except rectrices and remiges which are Sepia, white superciliary stripes with irregular Greenish Olive (49) patches, no crown stripe and no well-defined pectoral band, ventral regions Greenish Olive (49) slightly striated with Medium Neutral Gray (84) and white. As it matures, head becomes Greenish Olive (49) with Medium Neutral Gray (84) and discrete black; nape, back, rump, upper tail and wing coverts become Medium Neutral Gray (84) with Greenish Olive (49); ventral regions (chin, throat, breast, abdomen, and thighs) become white; black pectoral band appears; sides and flanks Medium Neutral Gray (84). All plumage has strong Buff (24) tone except rectrices and remiges. Greenish Olive (49) patches irregularly distributed over plumage especially on buffy white ventral regions, pectoral band and superciliary stripes.

Measurements. (n: m = 32 / f = 46). Mean values in mm, male (m), female (f). Bill length = 16.72 (m), 16.87 (f); bill width = 7.13 (m), 7.28 (f); bill height = 7.46 (m), 7.51 (f); wing length = 70.95 (m), 76.22 (f); tail length = 60.52 (m), 65.32 (f).

Distribution. Southwestern Brazil from western São Paulo to Mato Grosso do Sul, southern Mato Grosso, northern and western Paraná, and eastern Bolivia, Paraguay and north-eastern Argentina.