Why do male ducks often sound different from female ducks?

In many duck species, males and females sound different primarily due to anatomical differences in their vocal structures. Most male ducks possess an asymmetrical, bony chamber at the base of the trachea known as a bulla. This structure, which varies in shape and complexity across different species, influences the sounds produced, often resulting in the male’s characteristic whistle as opposed to the female’s quack.1

While the analogy of the trachea to a wind instrument is often used to explain how these birds produce sound, the specific relationship between the shape of the bulla and the resulting vocalization remains complex and difficult to fully account for. These vocal differences are particularly notable in groups such as the dabbling ducks and sea ducks, where sexual dimorphism in voice, plumage, and behavior is common. In contrast, other waterfowl, such as swans and geese, typically exhibit similar voices between the sexes.12