A large (22-27 inches) duck, the male Common Merganser is most easily identified by its green head, pale body, and thin red bill. The female Common Merganser is gray above and pale below with a rusty head and crest. In flight and at a distance, both sexes may be distinguished from the related Red-breasted Merganser (Mergus serrator) by the former species’ larger size and paler overall body pattern. Duck hunters often call mergansers “saw-bills” in reference to their long, thin, serrated bills. The Common Merganser has a wide distribution across the Northern Hemisphere. In North America, this species breeds across southern Alaska, Canada, and the northern United States. Smaller populations occur further south at higher elevations, particularly in the western U.S., where this species breeds locally south to Arizona and New Mexico. In winter, all populations migrate south, and may be found in coastal Alaska and Canada, in much of the U.S.outside of the southeast and northern Great Plains, and in northern Mexico. In the Old World, this species breeds across northern Europe, Scandinavia, and Russia, wintering south to North Africa, India, and Southeast Asia. As this species generally nests in tree cavities, Common Mergansers primarily breed on small bodies of water surrounded by woodland. In winter, this species may be found on large bodies of freshwater, including lakes, rivers, bays, and freshwater portions of large estuaries. Common Mergansers eat small animals, primarily fish and aquatic invertebrates. As this species is one of several “diving ducks,” Common Mergansers may be observed submerging themselves to feed in the water or on the bottom. In winter, they may also be observed in small flocks on large bodies of water. Like other mergansers, the Common Merganser undertakes swift, straight flights between bodies of water or on migration. This species is primarily active during the day.
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Bibliographic Citation: Rumelt, Reid B. Mergus merganser. June-July 2012. Brief natural history summary of Mergus merganser. Smithsonian's National Museum of Natural History, Washington, D.C.
