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Forest and Rangeland Birds of the United States

Natural History and Habitat Use

Common Merganser -- Mergus merganser

RANGE: Breeds in North America from central and south-coastal Alaska, northern Saskatchewan, and Newfoundland south to the mountains of central California and northern New Mexico. East of the Rockies, breeds south to southern Saskatchewan, central Michigan, southern Maine, and west-central Nova Scotia. Winters from the Aleutian Islands and south-coastal Alaska east across southern Canada to Newfoundland and south to southern California and the Gulf Coast from southern Texas to central Florida. Winters as far north as open inland waters are available.

STATUS: Common throughout range.

HABITAT: Prefers to breed in ponds associated with upper portions of rivers in forested regions, and clear, freshwater lakes with forested shorelines. Is transcontinental in character, but essentially confined to forested regions.

SPECIAL HABITAT REQUIREMENTS: Clear, forested streams, rivers, and lakes with tree cavities.

NEST: Generally nests in cavities in hollow trees near water, but also in dark recesses, on the ground, or in nest boxes. Height of tree cavity and species of tree are unimportant, but the number of suitable cavities available is definitely limited. May nest beneath boulders, in root tangles along undercut streambanks, in crevices in cliffs, or in chimneys, as long as the nest is concealed from above. One pair may use 2 to 3 miles of river during nesting.

FOOD: An opportunistic forager, generally feeds in fairly shallow waters from 1 1/2 to 6 feet deep. Consumes a wide variety of fishes, primarily rough and forage fish, but may be detrimental in areas specifically managed for trout or salmon production. Also eats frogs, aquatic salamanders, crayfish, shrimp, and other small crustaceans, snails and other mollusks, leeches, worms, aquatic insects and their larvae, and the roots and stems of aquatic plants.

REFERENCES: Bellrose 1976, Johnsgard 1975b, Palmer 1976b, Terres 1980, Timken and Anderson 1969.

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