Guide to Boreal Birds
Although preferring to feed on lakes, Common Mergansers are often driven to rivers by cold weather; there they are found in flocks of 10 to 20 birds, all facing upstream and diving in pursuit of fish. The narrow bill, with a hooked upper mandible and fine, saw-like teeth along the edges, is specialized to catch slippery fish. Pairs are formed in late winter, and until then one is likely to find flocks composed entirely of males or of females.
22-27" (56-69 cm). Male has flashing white sides, green head, white breast, and long, thin red bill. Female has gray body and sides; reddish-brown crested head sharply set off from white throat. Red-breasted Merganser is similar, but male has gray sides, white neck ring, and rust-colored breast; female has reddish-brown head that blends into gray of neck.
Low rasping croaks.
9-12 pale buff or ivory eggs in a down-lined tree cavity or sometimes on the ground or in an abandoned hawk's nest.
Breeds on wooded rivers and ponds; winters mainly on lakes and rivers, occasionally on salt water.
Breeds across Canada from eastern Alaska, Manitoba, and Newfoundland south in mountains to California, northern New Mexico, Great Lakes, and northern New England. Winters south to northern Mexico, Gulf Coast states, and Georgia (rarely farther). Also in Eurasia.