Gadwalls are medium-sized, streamlined ducks with mottled brown-and-black body plumage and light brown heads. Females and males in eclipse plumage may look superficially similar to Mallards. Both sexes have a black and white wing-patch, or speculum, that is distinctive in flight. Males also have chestnut on the forewing. Males in breeding plumage have gray and black striations on their bodies and heads, and black rumps. Females, immatures, and eclipse-plumaged males have thin, black bills with orange on the sides, while males in breeding plumage have solid black bills.