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Common Eider Life History

Habitat

Habitat Oceans

Common Eiders live mainly in marine waters, usually near rocky seacoasts. For nesting, they use low-lying coastal islands, islets, and shorelines with grasses, mosses, and sometimes low shrubs or stunted trees. High Arctic tundra heath, gravel spits, krummholz (very stunted trees), and taiga all serve as nesting habitat. On some islands, they nest near small lakes, usually those close to saltwater. Young remain with females in sheltered saltwater environments with abundant marine algae. The young often group into large flocks known as crèches, During migration or when preparing ("staging") for migration, large eider flocks sometimes use freshwater lakes and lagoons. Common Eiders typically winter in areas with rocky seafloors and strong tides, places that are generally rich in mollusks. The sedentary Hudson Bay Eider winters in polynyas (areas of open sea within the sea ice) and in cracks and leads in the ice.

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Food

Food Aquatic invertebrates

Adult Common Eiders eat almost exclusively mollusks, crustaceans (such as spider crabs), echinoderms (sea urchins), marine worms, and fish eggs. In strongly tidal areas, they tend to feed more at low tides. Among their favorite foods are blue mussels, which they pry from underwater rocks with chisel-like bills. In winter, green sea urchins are important in the diet; these are usually brought to the sea surface for processing before being consumed. Small prey items are swallowed underwater. Ducklings eat some marine algae along with gastropods (such as periwinkles) and amphipods (tiny crustaceans). Nesting females eat little but often pick at smaller prey in shallows when with young.

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Nesting

Nest Placement

Nest Ground

Females typically select a site within walking distance of the sea, often reusing the site from the previous season. The nest usually features some form of cover such as rock, driftwood, or vegetation.

Nest Description

Females make a depression in the ground using feet and belly. They line the scrape with their down only after laying their third egg. If females have to leave the nest, they often cover the eggs with the down. Nests are about 10 inches in diameter, with the interior cup about 8.5 inches across and 2.7 inches deep.

Nesting Facts

Clutch Size:3-8 eggs
Number of Broods:1 brood
Egg Length:3.0-3.1 in (7.55-7.84 cm)
Egg Width:1.9-2.1 in (4.92-5.28 cm)
Incubation Period:24-26 days
Egg Description:Olive or greenish, usually unmarked.
Condition at Hatching:Covered in down and able to leave the nest soon after hatching.
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Behavior

Behavior Surface Dive

Common Eiders appear to be monogamous, though males will display to females other than their primary partner. Pairs sometimes reunite in consecutive seasons. During periods of calm weather in autumn, males begin to display, both singly and in groups, tossing their heads, stretching their necks, and flapping their wings while keeping up a soft cooing. Pairs often copulate during fall and winter, well outside of the nesting season. Females respond to partners with a low cawing call. Females select the nest site, usually within a large colony of their species (except "Pacific" Eider, which often nests alone) and make their famous nests of down. Common Eiders also sometimes use nests of other waterfowl or gulls. Males remain near females during much of incubation, then move to less sheltered waters to molt and feed heavily. Males seem to be less aggressive toward each other than in some duck species, though both sexes lower the head and lift the chin in threat displays. Conflicts sometimes occur between pairs nesting close together.

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Conservation

Conservation Low Concern

Partners in Flight estimates a current global breeding population of 2.3 million, with an estimated 750,000 breeding in North America. The group rates Common Eider a 12 out of 20 on the Continental Concern Score, indicating a species of relatively low conservation concern. Market hunting reduced southern populations of Common Eider in the Atlantic to near extinction by the end of the nineteenth century, but their numbers increased in the twentieth century. Arctic populations are declining, in part due to hunting and to contamination by oil spills, toxic heavy metals, and lead shot. The overharvest of Common Eiders’ main prey species (blue mussels, green urchins) as well as algae—and the creation of aquaculture farms in sheltered coves—have reduced food available to them. Eiders can drown if they become entangled in monofilament gill nets set for lumpfish and flounder. Disruption of nesting activities on nesting islands can also reduce breeding success.

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Credits

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

Goudie, R. Ian, Gregory J. Robertson and Austin Reed. (2000). Common Eider (Somateria mollissima), 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. Longevity records of North American birds. Version 2020. Patuxent Wildlife Research Center, Bird Banding Laboratory 2020.

Partners in Flight. (2020). Avian Conservation Assessment Database, version 2020.

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

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