Sub-category: Ducks, Geese, & Swans
It eats fish and nests in holes in trees. Like the other mergansers, these fish-feeding ducks have serrated edges to their bills to help them grip their prey; they are therefore often known as 'sawbills'. In addition to fish, they take a wide range of other aquatic prey, such as molluscs, crustaceans, worms, insect larvae, and amphibians; more rarely, small mammals and birds may be taken.
It is 23 to 28 inches long with a 31 to 38 inch wingspan; males average slightly larger than females but with some overlap. Like other species in the genus Mergus, it has a crest of longer head feathers, but these usually lie smoothly rounded behind the head, not normally forming an erect crest. Adult males in breeding plumage are easily distinguished, the body white with a variable salmon-pink tinge, the head black with an iridescent green gloss, the rump and tail grey, and the wings largely white on the inner half, black on the outer half. Females, and males in "eclipse" (non-breeding plumage, July to October) are largely grey, with a reddish-brown head, white chin, and white secondary feathers on the wing. Juveniles (both sexes) are similar to adult females but also show a short black-edged white stripe between the eye and bill. The bill and legs are red to brownish-red, brightest on adult males, dullest on juveniles.
They are found on both saltwater and fresh water streams, ponds, and lakes.