Common Merganser, Mergus mergaser

Common Merganzer, Mergus merganser. Bird photographed in the Deschutes River in Bend, Oregon, September 2019.

Background and Identification

The Common Merganser, Mergus merganser, is a member of the Anatidae Family of Ducks, Geese, and Waterfowl. In Europe, they are also known as the Goosander. These ducks are large and elegant, often seen diving for their prey. Their diet consists primarily of a wide variety of fishes and limited amounts of aquatic invertebrates. Within their geographical range, they are very common and can be found along rocks in the midstream of rivers, or flying along the water. Birders and scientists can look for them in large flocks mixed with other species, such as the Common Goldeneye, Bucephala clangula, and the Bufflehead, Bucephala albeola. In Mexico, this species is known as Serreta Grande.

 This species is a large diving duck. Adults are strongly sexually dimorphic in size and plumage most of the year. The average male length is 60 cm (2 feet 0 inches) to 71 cm (2 feet 4 inches) and they have masses averaging from 1.30 kg (2 lbs 14 oz) and 2.1 kg (4 lbs 10 oz). Females average 54 cm (21 inches) and 68 cm (2 feet 3 inches) in length and have an average mass of 1.23 kg (2 lbs 8 oz). Males are striking, with a dark green head, bright red bill, and a white body tinged with a salmon hue during the breeding season. Females are more subdued, with a reddish-brown head, white chin, and gray body. Both sexes have serrated bills, which help them grip slippery prey like fish. Juveniles resemble females but have a more muted plumage. Common Mergansers are expert divers, often seen gliding on water or swiftly plunging underwater to hunt.

Habitat and Geographical Range

This species is found in clear freshwater lakes, ponds, and the headwaters of rivers near trees. Freshwater lakes are usually preferred, and anywhere else with an abundance of fish and invertebrates.

The Common Merganser is a migratory bird, traveling in the winter to ice-free waters, lower elevations, and more temperate regions. They breed in northern regions, including Canada, the northern United States, and across much of Europe and Asia. In North America, wintering birds can be found across the United States, particularly in large lakes and rivers. In Mexico, they are wintertime visitors and are found in the northern parts of the country in the States of Baja California, Baja California Sur, Durango, Sonora, Tamaulipas, and Zacatecas at elevations below 2,800 m (9,200 feet).

Common Misidentifications

The Common Merganser is sometimes confused with other merganser species, particularly the Red-breasted Merganser, Mergus serrator. However, the Red-breasted Merganser is smaller, with a thinner, more shaggy crest and more subdued body markings.

Conservation Perspective

From a conservation perspective the Common Merganser is currently considered to be of Least Concern with stable, widely distributed populations. However, localized threats such as water pollution, habitat destruction, and disturbance to nesting areas could affect certain migrating populations. Conservation efforts aimed at maintaining healthy water ecosystems help ensure their continued survival.