The red-breasted merganser (Mergus serrator) is a diving duck, one of the sawbills. The genus name is a Latin word used by Pliny and other Roman authors to refer to an unspecified waterbird, and serrator is a sawyer from Latin serra, "saw".
It has a spiky crest and long thin red bill with serrated edges. The male has a dark head with a green sheen, a white neck with a rusty breast, a black back, and white underparts. Adult females have a rusty head and a grayish body. Juveniles look similar to females, but lack the white collar and have smaller white wing patches.
The call of the female is a rasping prrak prrak, while the male gives a feeble hiccup-and-sneeze display call.