The upperparts of this species are dark steely-grey to blue-grey with darker slate-grey flight feathers. The flight feathers show faint dark banding in flight, at least on the primaries. The relatively long, broad, round-tipped tail is dark grey above and paler grey below, with 3-5 dark slate-grey bands and a narrow whitish tip. The underparts are whitish with dense, fine, dark grey barring on the breast, belly, sides, and flanks (often nearly obscuring the white background) and variable amounts of fine blackish streaking; the bushy undertail coverts are white. The underwing coverts are densely barred with dark grey and are similar in colour to the underparts. The crown and nape are dark slate-grey to blackish, and are separated from the blackish ear coverts by a bold white supercilium. The throat and cheeks are whitish with very fine blackish or dark grey streaking. Females are slightly browner than males, and have coarser and heavier dark barring and streaking on the underparts. The iris is red (orange in younger adults), the bill is dark grey with a yellow cere, and the legs and feet are yellow.
This plumage is held for approximately one year and is usually lost during the second summer of life. In this plumage, the upperparts are brownish with paler brown or buffy edges to the feathers and, often irregular buffy patches on the scapulars and a buffy band across the upperwing coverts. The flight feathers are grey-brown with darker grey barring and narrow buffy or whitish tips. The tail is similar in pattern to that of the adult, but is browner and often shows very narrow whitish edges, or “highlights,” to the wavy dark bands. The underparts are whitish to buffy with variable (often heavy) dark brown streaking across the breast, belly, sides, and flanks and often some coarse, dark brown barring on the sides; the undertail coverts are usually whitish with dark brown streaking. The crown, nape, and ear coverts are buffy-brown with narrow dark brown streaking and a bold, white supercilium. The throat and cheeks are whitish or buffy-white with variable amounts of narrow dark brown streaking (heaviest on the malar). The iris is yellow, but bare part colouration (bill, legs, feet) is otherwise similar to the adult.
Total Length: 53-66 cm (f >m)
Mass: 693-1,036 g (f >m)
Source: Squires and Reynolds (1997); Taylor (2006)