Capuchinbird is a large, odd looking bird with a short tail, bald blue gray head and a heavy bill. The plumage is mostly ochre brown, darker on the rump, and is reddish chestnut on the belly. The undertail coverts, which are orange rufous, are long and curled in the male, and are capable of being raised out like globular orangish "tail lights" during lekking displays. The undertail coverts of females, however, are not lengthened. The wings and tail are blackish, with white underwing coverts.
Restall (2006) et al. suggested that Capuchinbird may "recall a small Black Vulture [Coragyps atratus] with its bare head and uniform mantle".
Wthin its range Capuchinbird is essentially unmistakable. The combination of its "cowled" head, large size, and ochraceous brown coloration contribute to a strange but unique appearance.
The following detailed description is based on Kirwan and Green (2011):
Adult: Sexes similar, although the male is larger (see Measurements) and has longer undertail coverts. Large, bulky, with short tail, heavy bill, and bare crown. Upperparts generally dill cinnamon. Feathers on the back of the head dense and upright standing, forming a prominent cowl, and imparting a "hunchbacked" appearance. Uppertail coverts blackish with dull cinnamon tips. Remiges blackish, outer webs of the tertials with brownish fringes. Rectrices black. Underparts deeper cinnamon, especially from the breast to the vent. Undertail coverts of male long and orange rufous; undertail coverts short in female. Underwing coverts creamy white.
Juvenile: Similar to adult, but has sparse down on the bare areas of the head.
Nestling: Covered in orange down.
Little information. Molt apparently is very protracted, and may extend over as many as 220 days (Snow 1976). In Guyana molt is initiated in March-July, but in other regions the timing of molt is less well defined (Kirwan and Green 2011).
Iris: dark brown
Bare skin of crown and sides of head: gray blue with sparse hair like feathers
Bill: maxilla black, mandible grey
Tarsi and toes: dark blue gray
Bare part colors data from Snow (1982).
Total length: 34.5-35.5 cm (Ridgely and Tudor 2009), 36 cm (Hilty 2003)
Linear measurements (from Snow 1982, and based on museum specimens except with otherwise indicated):
males (n = 16):
wing length: mean 217.3 mm (range 210-232 mm); mean wing length of live individuals, 225.0 mm (n = 5)
tail length: mean 103.2 mm (range 100-107 mm)
tarsus length: mean 43.1 mm (range 41-45 mm)
culmen length: mean 35.7 mm (range 32-38 mm)
females (n = 10)
wing length: mean 203.1 mm (range 197-210 mm); mean wing length of live individuals, 221.5 mm (n = 6)
tail length: mean 100.2 mm (range 96-104 mm)
tarsus length: mean 40.0 mm (range 38-42 mm)
culmen length: mean 32. mm (range 31-33 mm)
Mean wing-length: 212.5mm
Mass: male, mean 360.0 g (range 320-395 g, n = 5; Snow 1982)
female, mean 319.0 g (range 267-367 g, n = 6; Snow 1982)