Adult male
The upperparts (back, scapulars, rump) are unmarked grey. The wings are blackish with narrow grey feather edges on the flight feathers and upperwing coverts as well as two bold, white wing bars. The slender, square-tipped or slightly notched tail is blackish with narrow grey outer edges to the feathers and extensive white on the inner webs of all but the central pair of feathers (white patches diminishing in size from outer edge of tail towards central tail feathers). The forehead is black, extending onto the grey crown as narrow black streaks; the nape and hindneck are clear grey. The lores and ear coverts are black, separated from the dark crown by a long, narrow white supercilium, and separated from the grey sides of the neck by an oval-shaped white patch; depending on the subspecies, there may be a yellow loral spot on the front portion of the supercilium between the eye and the bill. The black ‘mask’ extends down the side of the throat and onto the sides of the breast, where it breaks into bold, irregular black streaks and spots that continue down the sides and flanks of the otherwise white underparts. There is a narrow white crescent below the eye. The throat and upper breast are bright yellow, often separated from the bill by a white chin (depending on subspecies). The iris is dark, the short, slender, pointed bill is blackish, and the legs and feet are dusky-grey.
Adult female
The adult female is very similar to the adult male, but is slightly duller overall, with reduced black on the crown and narrower, greyer streaks on the sides and flanks. The white in the outer tail feathers is less extensive than in the male, and is primarily confined to the two outermost feathers.
Immature
All immature plumages (which are held throughout the first fall and winter) resemble the adult female, but are even duller (particularly immature females). Immature males are very similar to adult females, and some may not be distinguishable. Immature females, however, have the grey of the face replaced with dark grey, and have less extensive and greyer streaking on the sides and flanks; immature females often have a slight brownish tinge to the plumage as well as reduced yellow on the throat, and the white in the outer tail feathers is even less extensive.
Measurements
Total Length: 12.5-14 cm
Mass: 9-11 g
Source: Curson et al. (1994); Hall (1996); Dunn and Garrett (1997)