The colors on the male common merganser -- the long white sides and the breast contrasting with the dark head and dark back -- show a pattern unlike any other waterfowl. Although this bird can be seen from far away on a calm river or lake, the dark and white patterns match the dark shadows and sunlit patches of the forest and the dark water and white rapids of the stream. These colors are an adaptation for being perfectly "hidden" while spending summer nesting seasons in, over, and near a forest stream.

The females are better camouflaged than the males. Their back and sides are gray, their head reddish brown with a crest of feathers protruding off the back of the head. Other adaptations for both the male and female include a long, straight bill, with a saw-edged upper mandible to be able to hold onto fish.

When feeding, mergansers dive quickly with a forward curving plunge. They swim swiftly underwater. Their diet is minnows, sticklebacks, suckers, fish eggs, insects, larva and crustaceans.

In that hidden place by the mountain lake or stream the female lays 8 to 11 eggs. She incubates for about 30 days. When the young leave the nest after 24 to 48 hours they can find their own food and follow their mother. She tends the young until they can fly in 70 days.