Like all mergansers, it has a long, narrow, serrated bill. It has a brownish-black back and wings, with a white underside. The male has a black head with a white, fan-shaped crest, which is bordered in black. Reproduction Pair formation occurs in November or December. Only monogamous pairs have been documented.
Females select the nest site, which is usually a cavity in a dead or live tree.
Nest boxes, along with already built and abandoned nest sites, are preferred. Cavities are usually 4-15 feet off the ground. Between 7 and 15 eggs are laid shortly after the nest is completed. Incubation begins after all the eggs have been laid. The male abandons the female shortly after this point.