The White-collared Seedeater is a typical Sporophila: it is a small finch with a short, stubby bill. Males in alternate plumage have a prominent white throat and have white outer webs to the primaries, forming a prominent white spot along the folded wing. In most subspecies there is a black breast band and a prominent partial white collar; although in northern populations, however, this breast band is incomplete and is confined to the sides of the breast, and males do not acquire the white collar. Alternate plumaged males (except for atriceps and nominate torqueola), also have two white wing bars.
Females are much less patterned, and are buffy brown above and whitish buff below. Females of most subspecies (except for atriceps and nominate torqueola) also have two white wing bars. Males in basic plumage are similar, but retain the white spot at the base of the primaries.
The White-collared Seedeater overlaps geographically with two other species of Sporophila, the Ruddy-breasted Seedeater (Sporophila minuta) and the Variable Seedeater (Sporophila corvina). The male Ruddy-breasted Seedeater in alternate plumage easily is distinguished by two-toned plumage, gray above and ruddy below. Female and basic-plumaged male Ruddy-breasted are more similar to female White-collared, but Ruddy-breasted is smaller than the White-collared, with a paler bill and more contrasting wing edgings. It also lacks the obvious wingbars, which distinguishes it from most subspecies of White-collared (except for nominate torqueola). The male Variable Seedeater is almost all black, and so easily is distinguished. Female Variable Seedeater does not have wingbars, and is more olive in color.
The following description applies to nominate torqueola, and is based on Ridgway (1901); for the characters of other subspecies, see Geographic Variation:
Adult male, alternate plumage: Crown, lores, auriculars, and center of nape black. Back, scapulars, and uppertail coverts black. Rump cinnamon. Wings black, except for white bases to both webs of primaries (except for the three outermost primaries, which are entirely black). Throat and malar pale buffy, continuous with white sides of the neck. Black band across upper breast. Lower breast, belly, crissum and undertail coverts pale cinnamon or ochraceous-buff. Rectrices black.
Adult male, basic plumage: Similar to adult female, but has white bases (including outer webs) to primaries (except for the outer three).
Adult female: Upperparts plain light olive, paler on rump. Underparts yellowish buff; paler on center of belly, darker and tinged with olive on breast and flanks.
Little known. Believed to have two annual molts (Eitniear 1997), although "because males in breeding plumage can be found at any time of year in Mexico (with a marked summer peak corresponding to the rainy season), their breeding aspect might not correlate strictly to an alternate plumage" (Howell 2010: 229). Also, "number of years it takes for males to acquire Definitive plumage has been debated," with estimates ranging from two to three years (Eitniear 1997).
Iris: brown, hazel (Field Museum of Natural History)
Bill: black (Field Museum of Natural History)
Tarsi: dark brown, black (Field Museum of Natural History)
Total length: 10 cm (Stiles and Skutch 1989), 10-11.5 cm (Howell and Webb 1995)
Linear measurements: (from Wetmore et al. 1984, for morelleti):
wing length, males: mean 51.1 mm (range 49.3-52.5 mm, n=10)
wing length, females: 50.0 mm (range 48.0-52.4 mm, n=10)
tail length, males: mean 44.2 mm (range 42.0-46.5 mm, n=10)
tail length, females: mean 42.4 mm (range 39.6-46.0 mm, n=10)
culmen (from base), males: mean 9.4 mm (range 8.6-9.9 mm, n=10)
culmen (from base), females: 9.6 mm (range 9.0-10.2 mm, n=10)
tarsus, males: 15.2 mm (range 14.8-15.9 mm, n=10)
tarsus, females: 14.7 mm (range 13.3-15.3 mm, n=10)
Mass: both sexes combined, mean 8.7 g (range 6.3-12 g, n=41; Dunning 2008)