The Red-breasted Merganser (Mergus serrator) is a diving duck. Its breeding habitat is freshwater lakes and rivers across northern North America, Greenland, Europe and Asia. It nests in sheltered locations on the ground near water. It is migratory and many northern breeders winter in coastal waters further south. The adult Red-breasted Merganser is 52–58 cm long with a 67–82 cm wingspan. It has a spiky crest and long thin red bill with serrated edges. Adult males have 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 greyish body. Juveniles are like the female, but lack the white collar and have a smaller white wing patch.