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Black Scoter Life History

Habitat

Habitat Oceans

Black Scoters nest in the boreal forest of the far north, near shallow, small lakes that usually have rocky bottoms and some emergent vegetation along the edges. After nesting, they gather in flocks for a period of molting, which lasts about 3 weeks in specific locations such as Bristol Bay, Alaska, or the St. Lawrence River. Late autumn migration occurs across a broad front, so migrants may turn up almost anywhere in the continent’s interior, usually on lakes and larger rivers, where they normally do not linger long. From late fall through early spring, flocks congregate along ocean and bay coastlines, wherever water is relatively shallow and shellfish such as mussels are abundant. They winter in waters with both rocky and sandy bottoms. On the Pacific coast, some Black Scoters frequent congregations of seabirds that feast on the herring spawn in early spring.

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Food

Food Aquatic invertebrates

Breeding Black Scoters consume large quantities of insects and their larvae, notably caddisfly, mayfly, and beetles, small mollusks and crustaceans (such as amphipods), as well as fish eggs. Their summer diet also includes vegetation, including iris, pondweed, duckweed, and milfoil. In winter, Black Scoters eat mostly shellfish, especially mussels and clams, along with crustaceans and smaller amounts of marine vegetation such as eelgrass. Prey include blue mussel, black mussel, scallop, razor clam, Arctic wedge clam, small sea clam, softshell clam, hard rock clam, tortoise shell limpet, northern red chiton, chink shell, obtuse periwinkle, top shell, northern astarte, sea snail, and goose barnacle. Polychaete worms, crabs, and shrimp make up smaller parts of the diet.

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Nesting

Nest Placement

Nest Ground

The nest is usually within 100 feet of the water’s edge in a grassy spot that offers some shelter and lacks standing water. Nests are sometimes placed on mossy ground or in a clump of small trees.

Nest Description

The female makes a depression in the ground, usually in sedge or grass, and lines it with her own down feathers. Nests measure about 9.8 inches across and 4.9 inches tall, with interior dimensions 6.9 inches across by 4.5 inches deep.

Nesting Facts

Clutch Size:8-9 eggs
Number of Broods:1 brood
Egg Length:2.5-2.6 in (6.26-6.53 cm)
Egg Width:1.7-1.8 in (4.4-4.5 cm)
Incubation Period:27-28 days
Egg Description:

Off-white to pinkish buff.

Condition at Hatching:

Downy and eyes open. Leave nest soon after they dry. Feed themselves immediately.

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Behavior

Behavior Surface Dive

Beginning in December, adult males perform courtship displays in a specific sequence: they stretch out the neck, raise the tail skyward, then flatten out and rush forward with much splashing. They then dip the bill and flick water upward, preen the breast, stretch the head out low again, rise up, and shake the head side to side. Males also perform short flights that conclude with an exaggerated feet-first landing and wing-flap. Females often fend off displaying males by rushing forward toward them. A female that fancies a particular male begins to display with him, incorporating most of the same moves. Winter courtship often occurs in groups, with many males seeking to impress females simultaneously. On the breeding grounds, Black Scoter pairs are socially monogamous, but their mating system is little studied. Males closely guard mates, chasing away any male that comes near. Females also drive out other females, usually with a lowered head (threat display) or a chase. After egg-laying, males quickly depart toward molting areas, and females incubate the eggs and care for the young.

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Conservation

Conservation Low Concern

Black Scoters nest in the remote north, making their population trends hard to estimate, but they appear to be in decline. A 1993 study of eastern North America estimated a decline in all 3 scoter species at 1% per year between 1955 and 1992, indicating a cumulative decline of 31% over that period. Partners in Flight estimated the 2017 global breeding population at about 500,000 and rated the species a 12 out of 20 on its Continental Concern Score, indicating a species of low concern. The International Union for the Conservation of Nature lists Black Scoter as "Near Threatened." Like most waterfowl, Black Scoters are hunted with seasons managed closely by the U.S. Fish and Wildlife Service. In recent years, the total hunt of all 3 scoter species in all of the U.S. ranged from about 48,000 to 84,000 per year. Other conservation issues include climate change, contaminants, and possibly oil and gas drilling in nesting areas.

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Credits

Bellrose, F. C. (1976). Ducks, Geese and Swans of North America. Second edition. Stackpole Books, Harrisburg, PA, USA.

Bordage, Daniel and Jean-Pierre L. Savard. (2011). Black Scoter (Melanitta americana), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Lutmerding, J. A. and A. S. Love. (2019). Longevity records of North American birds. Version 1019 Patuxent Wildlife Research Center, Bird Banding Laboratory 2019.

Partners in Flight (2017). Avian Conservation Assessment Database. 2017.

Raftovich, R.V., K.K. Fleming, S.C. Chandler, and C.M. Cain. 2019. Migratory bird hunting activity and harvest during the 2017–18 and 2018-19 hunting seasons. U.S. Fish and Wildlife Service, Laurel, Maryland, USA.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

U.S. Fish and Wildlife Service. (1993d). Status of sea ducks in eastern North America. Laurel, MD: U.S. Fish and Wildlife Service, Office of Migratory Bird Management.

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