Antshrikes are medium to large sized antbirds with stout, hooked ("shrike"-like) bills and relatively long tails. Spiny-faced Antshrike takes its English name from a feature that rarely is evident in the field, a cluster of short black bristles on the lores, and from the area below the eye down to the chin. The sexes of Spiny-faced Antshrike differ in plumage, but both have brown upperparts, the feathers of which are margined with black, produced a vaguely spotted or streaked pattern (an alternative English name is Streaked Antshrike). The underparts of the male are slate gray, where the female is pale olive brown, indistinctly spotted with blackish. Both sexes have prominent buff wing bars across the wing coverts.
Spiny-faced Antshrike is very distinctive, and is unlikely to be confused with any other species in its range. The pattern of the male - with underparts that are darker than the upperparts - is unique within its range. Female Spiny-faced Antshrike somewhat resembles female Black-crowned Antshrike (Thamnophilus atrinucha) or female Dusky Antbird (Cercomacra tyrannina), but differs from both in many ways: neither of these species are speckled or spotted above, female Dusky Antbird lacks wing bars, female Black-crowned Antshrike is a much duller brown and its wing bars are white (not buff), etc. Female Spiny-faced Antshrike perhaps also could be confused with a foliage-gleaner or other furnariid, but note the antshrikes prominent buff wing bars and the distinctly hooked bill.
The following description is based on Wetmore (1972) and Zimmer and Isler (2003):
Both sexes have short but well developed black bristles on the lores, below the eye, around the gape, and on the chin.
Adult male: Forecrown dark gray. Crown, nape, back, and scapulars olive brown to buffy brown, each feather margined and tipped with black, giving a somewhat spotted appearance, the spots tending to form a series of dark lines down the upperparts. Rump and uppertail coverts gray, washed with olive brown. Rectrices blackish slate. Wings dusky brown, the wing coverts tipped with deep buff. Primaries narrowly edged with brown; scapulars and inner secondaries tipped with brown. Sides of head and entire underparts slate gray.
Adult female: Upperparts like male. Chin dull white. Throat whitish olive with small blackish brown spots. Breast and sides pale olive brown; feathers of breast with blackish margins, producing indistinct spotting. Flanks and vent darker.
Juvenile and immature: Undescribed.
Iris: pale gray
Bill: maxilla black, with gray tomia; mandible gray, distal tomia black
Tarsi and toes: dark gray
Bare parts color data from Wetmore (1972).
Total length: 15 cm (Hilty and Brown 1986), 15-16 cm (Wetmore 1972)
Linear measurements (from Wetmore 1972):
male (n = 4)
wing length: mean 71.1 mm (range 69.8-72.5 mm)
tail length: mean 63.8 mm (range 59.1-69.2 mm)
bill length (culmen from base): mean 19.2 mm (range 18.8-19.5 mm)
tarsus length: mean 22.2 mm (range 22.2-22.3 mm)
female (n = 7)
wing length: mean 71.0 mm (range 69.1-72.9 mm)
tail length: mean 62.7 mm (range 61.0-64.6 mm)
bill length (culmen from base): mean 20.2 mm (range 19.3-21.0 mm)
tarsus length: mean 22.3 mm (range 22.0-22.9 mm)
Mass: 24.6 g (n = 1, female; Dunning 2008)