Common Merganser

Overview

The Common Merganser, known as the Goosander in parts of its Eurasian range, is the largest of the mergansers, favoring clear rivers, lakes, and reservoirs. Breeding males show a smooth, glossy dark green head, a black back, and a strikingly clean white body that can show a subtle salmon-pink wash early in the season. Females have a reddish-brown crested head sharply set off from a gray body by a clean white throat and chin, an important field mark distinguishing them from the similar Red-breasted Merganser.

Feather Identification

• Head-neck demarcation: Females show a sharp, clean-cut boundary between the reddish-brown head/neck feathering and the pale gray body, unlike the more gradual blending seen in Red-breasted Merganser.
• Male body color: The male's underparts appear nearly pure white, sometimes with a faint pinkish tinge, lacking the vermiculated gray flanks of Red-breasted Merganser.
• Crest shape: Both sexes show a crest, but it is looser and less shaggy than the double-pointed crest of the Red-breasted Merganser.
• Bill and head shape context: A straight, thin, serrated bill paired with a smoothly rounded head shape complements the body feather pattern for identification.
• Wing pattern: A large white patch on the inner wing is visible in flight, more extensive in males than females.

Plumage Notes

Breeding males show a glossy dark green head, black back, and clean white underparts, sometimes tinged pink. Females have a rusty-brown crested head, gray body, and a well-defined white chin and throat. Eclipse males resemble females but often retain a darker back. The species undergoes a complete post-breeding molt, with a flightless period while new flight feathers grow in. Juveniles resemble females, and young males acquire full adult head and body coloration over time.

Habitat & Range

Common Mergansers breed along clear rivers, lakes, and large ponds across the northern forested regions of North America and Eurasia, often nesting in tree cavities or other sheltered sites near water. In winter, they move to large rivers, lakes, and reservoirs that remain open, sometimes forming sizeable flocks. The species is migratory across much of its range but can remain resident where open water persists through the colder months.

Behavior & Field Notes

Common Mergansers are strong swimmers and divers, pursuing fish underwater with their thin, serrated bills. They often forage cooperatively, with groups working together to herd fish into shallower water. Nesting occurs in tree cavities or other sheltered sites near rivers and lakes, and broods of ducklings are frequently seen following the female closely. The species is relatively quiet, with occasional low croaking or grunting calls, and flight is fast and direct, typically low over the water in a line formation.