Appearance

The Black-headed Duck has a distinctive shape: the wings are relatively short, contributing a long-bodied appearance, which is accentuated by the relatively long bill and flat crown. This duck is relatively unpatterned. The male is mostly dark brown with a black head; the bill is bluish, and has a red spot at the base during breeding. The female is dusky brown above; the underparts and sides to the face are paler brown, spotted or vermiculated with dusky.

Distinguished from other species of ducks by distinctive body shape (long body, relatively short wings) and by its posture, with the body resting lower in the water than is the case for other species of ducks. The female somewhat resembles a female Ruddy Duck (Oxyura jamaicensis ferruginea), but the female Black-headed Duck has a suggestion of a pale supercilium, and pale sides to the face.

Sexes different, female larger than male. The following description is based on Blake (1977) and, for downy young, Weller (1967a).

Male: Head and upper neck glossy black. The chin usually is white; occasionally the  throat is white as well. The lower part of the foreneck is brownish. The upperparts are  deep brownish black, minutely speckled and vermiculated with cinnamon or pale rufous. The tips of the secondaries, and of their coverts, are white, forming two narrow white wing bars. The underparts are mainly whitish mottled with brown, giving a silvery appearance.

Female: "Head and neck mainly variegated brown, darkest above, throat whitish; in other respects much like male."

Immature: "Similar to female, but more rufous above, more yellowish and less mottled below, and with pale, distinct eye stripe."

Downy young: Blackish-brown and yellow pattern similar to other species, except that the yellow is dark, and yellow of facial area with orange-brown cast; distinctive vertical line from eye to crown; maxilla black with yellow edges, mandible dull yellowish, feet deep gray.

Molt of body feathers: natal to juvenile December-January; Juvenile to Basic January-March; Basic to Alternate July-August. Ssubsequent years Alternate to Basic January-February, Bbasic to Alternate July-August (Weller 1967a).

Except where noted otherwise, the following data are from Blake (1977):

Iris: brown

Bill: maxilla black, with rose pink patch at base. This red spot on the maxilla is seasonal, and is present only during breeding (Madge and Burn 1988, Jaramillo 2003). Mandible orange.

Tarsi and toes: dark grayish brown.

Females larger than males; data below from Weller (1967a):

Wing length (male): mean 169.3 mm (range 158-178 mm, n=54)

Wing length (female): mean 171.8 mm (range 154- 182 mm, n=42)

Tail length (male): mean 48.3 mm (range 44-57 mm, n=53)

Tail length (female): mean 51.7 mm (range 44-59 mm, n=42)

Mass (male): mean 512.6 g (range 434-580 g, n=11)

Mass (female): mean 565.2 g (range 470-630, n=13)