Adult male mallards are easily identified by their green head, chestnut breast, gray body, black back, and white-bordered blue speculum, which is the wing patch located on the secondary feathers. The females are brownish with an orange bill with dark saddle markings. Male vocalizations include a loud graeb-graeb or a whistle. Female vocalizations include a descending quacking sound (the males don’t quack) and various softer kegs and hey-hey-heys.
Similar species: The American black duck (A. rubripes) is an uncommon migrant or winter resident in Missouri. It has very dark brown body feathers, a light brown head, a greenish bill, and a purple speculum.