Muscovy Duck is a very large, heavy bodied duck. The feathers on the crown and on the rear of the neck are somewhat elongated, forming crests. There is extensive bare skin on the face; this skin is mostly black, with red or pink caruncles. The plumage is very dark in wild Muscovies, primarily black with a greenish gloss, and white wing coverts (on both the upper and under surfaces of the wing). Domesticated Muscovies usually show white blotches on the body plumage. The sexes are generally similar, but females are significantly smaller than males, the plumage is duller (less glossy) and with less white in the wings, and the female lacks the crest and facial caruncles. Juveniles are even duller (dark brown rather than black), with very little white in the wing (Johnsgard 1978).
Muscovy Duck is very distinctive, and is unlikely to be confused with any other species in its range. Black-bellied Whistling-Duck (Dendrocygna autumnalis) also has broad white wing patches, but is smaller bodied, is mostly brown (not black), and has a prominent red bill and longer, pink tarsi. Unlike any other species except domesticated varieties. Overall body shape similar to Comb Duck (Sarkidiornis melanotos) also is large, with a heavy body, but Comb Duck has a pale head, neck, and underparts, and its wings are entirely dark.
The following description is based on Wetmore (1965):
Adult male: Overall plumage is blackish, with a metallic greenish-purple cast on the upperparts, the gloss becoming more violet on the upper back. Prominent crest on crown and rear of neck. Wing coverts, on both the upper and under surfaces of the wing, white.
Adult female: Plumage similar to that of males but duller. Face fully feathered, not bare as in male.
Juvenile: Overall body coloration similar to adults, but is dull brownish black except for the green tertials and secondaries. The wings have little or no white; if present, reduced to a small spot on the greater coverts.
Duckling: Boldly patterned with yellow and dark brown, and have a prominent dorsal spots and wing patches (Nelson 1993). The forehead, the throat, and the sides of the head are yellow, with a conspicuous supraorbital stripe (Baldassarre 2014).
Muscovy Ducks, unlike Nearctic migratory species, do not have a different alternate (breeding plumage) but maintain a definitive basic plumage throughout the year.
Ducklings have a prebasic juvenile molt that produces a plumage aspect duller than that of the adult. After the Basic II plumage is obtained the plumage becomes definiative. Debate continues as to if the male Muscovy has a flightless wing molt (eclipse). Captive observations indicate they do but field studies do not seem to support the assertion (Hoffman 1992). Additional study of wild birds is needed to clarify the situation regarding molt in this species.
Adult male: Tarsi and toes black, with long sharp claws. Bill is black at base, with fleshy white mottling, a blackish band extending across the middle, and a pink spot near the tip. Bill also has a blackish to dark red knob at the base of the bill, with bare facial skin between the bill and the eyes; with red caruncles of varying size and numbers. The irides are brown or yellowish brown.
Adult female: Lacks bill knob and bare facial skin. Occasionally older females have a few caruncles. Tarsi and toes are dull blackish (Baldassarre 2014).
Juvenile: Like adult female, but the bill is gray.
Duckling: Tarsi and toes are a dull yellow, patterned with grayish brown (Baldassarre 2014).
Total length: 66-86.5 cm (Howell and Webb 1995); male, 76-84 cm, female 71-76 cm (Ridgely and Greenfield 2001b)
from Wetmore (1965):
male (n = 5): wing length, mean 385 mm (range 363-404 mm); tail length, mean 191 mm (range 182-198 mm); bill length (culmen, from frontal feathering), mean 69.9 mm (range 66.6-76.6 mm); tarsus length, mean 66.3 mm (range 63.2-70.0 mm)
female (n = 5): wing length, mean 308 mm (range 293-326 mm); tail length, mean 153 mm (range 142-167 mm); bill length (culmen, from frontal feathering), mean 54.8 mm (range 52.0-59.5 mm); tarsus length, mean 51.2 mm (range 45.9-55.0 mm)
from Leopold (1959):
male (n = ?): folded wing, range 400-450 mm; bill length, range 68-78 mm; bill length, range 68-78 mm
female (n = ?): folded wing, range 315-330 mm; tarsus length, range 50-59 mm; bill length, range 53-57 mm
Mass: male, 2685 g (n = 1; Haverschmidt 1968); male (n = ?), range 1,990-4,000 g (Leopold 1959); female (n = ?), range, 1,100-1,470 g (Leopold 1959)
Domestic birds can be much heavier.