Common Merganser (Mergus merganser)

This is an adult male in winter plumage. Although this species has increased rather dramatically in the San Francisco Bay Area I still seldom encounter very many adult males. This is partly because immature males and adult males in summer ("eclipse" plumage) resemble females. Common Mergansers are divided into two groups. Eurasian birds (sometimes known as Goosander) have a somewhat thinner bill with a stronger hook at the tip. Another difference is the entirely red bill of American birds. Goosander usually has the lower mandible partly black. Notice the more sloping head blending into the thicker bill base, another feature of the American population (subspecies "M. m. americanus").