Bird Lore: The Common Merganser

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The Common Merganser is the largest of the mergansers and one of the larger of all ducks. All three North American mergansers are distinguished from other ducks by their long, narrow bills with serrated edges. The Common Merganser is the typical merganser of freshwater lakes and rivers. It will also frequent coastal bays in winter. In Edmonds it can be seen along the waterfront and at Lake Ballinger. It is rarely seen in the Edmonds marsh. Although the Common Merganser is a resident species of Washington, it is absent from Edmonds waters from mid-May to late August. When it is present, it is usually seen in very small flocks and often just flying along the waterfront. LeRoy took the accompanying photos along the waterfront.

A wide variety of fish makes up most of the Common Merganser’s diet. The adult male has been known to swallow fish more than one foot in length. It will also feed on mussels, shrimp, and salamanders. It rarely eats plant materials. This merganser finds most prey by sight. As it swims, it dips its head underwater repeatedly until it spots a fish. It then dives in pursuit. While swimming underwater, it propels itself by stroking with both feet in unison.

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The nest site is near water and is usually in a large tree cavity. The Common Merganser will also use rock crevices and holes under tree roots or in undercut river banks. It will also use nest boxes when available. A cavity nest is filled with wood chips or debris and lined with down. There are typically 8-11 eggs. Females are known to lay eggs in each other’s nests. The female incubates the eggs for approximately one month. The young birds remain in the nest for a day or so after hatching. They then climb to the cavity entrance and jump to the ground. The female remains with the young for several weeks but they feed themselves, mostly eating aquatic insects. The young can fly 65 – 70 days after hatching.

The population of the Common Merganser is thought to have been stable over the last half century. Its conservation status is that of least concern. The only known area where its numbers are declining is the province of Manitoba. This merganser’s habitat can be degraded by acid rain, pesticides, and toxic metals. Its eggshells can become too thin for successful hatching, Food sources can be reduced in areas of degradation.

The oldest known Common Merganser lived thirteen and a half years. Although this species is not a prized game bird, some are shot every year, either for sport or by mistake. At times, humans have targeted this species for eradication out of fear that its existence threatened salmon and trout stocks. So it joins the ranks of other targeted species such as Double-crested Cormorants and Caspian Terns that are being harassed or killed to protect Columbia River salmon.

You can hear the calls of a Common Merganser hen at this link: http://www.xeno-canto.org/103685 . The calls of a drake are here: http://www.xeno-canto.org/171602.

— By Carol Riddell

Carol Riddell manages the bird education displays, on behalf of Pilchuck Audubon Society and Edmonds Parks & Recreation, at the Olympic Beach Visitor Station.

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