Steller’s eiders arrive on the breeding grounds paired up and often gather in small groups on open ponds. Once breeding activity begins to occur, pairs, but particularly the males of breeding pairs, will fight off others in close proximity and often rush at each other in water or running on land. Males in courtship behavior dip and raise their heads and maintain close proximity to the female. If startled, the pair may take flight, but often return shortly to the same pond. Steller’s eiders can walk quickly on land with a slight waddle. Males will stay on the breeding grounds part way into incubation, before breaking the pair bond to depart to the ocean. If disturbed, nesting females quickly return to the nest area. Nesting locations sometimes associated with pomarine jaegers (Stercorarius pomarinus), who aggressively defend their own nests. During the non-breeding season, Steller’s eiders may gather in the thousands in molting and wintering areas offshore in southwest Alaska.

Steller’s eiders are small sea ducks that in flight often fly in tight groups. They have a relatively small head and flat crown, short body, relatively narrow wings and an elongated, pointed tail.

Measurements
Length: 16.9 to 18.1 inches (43 to 46 centimeters)
Wing length: 80.3 to 89.4 inches (204 to 227 centimeters)

Steller’s eiders are the smallest of the four eider species and males and females are very similar.

Measurements
Average mass of adult males at Utqiagvik, Alaska: 31 ounces (887 grams)
Average mass of adult females at Utqiagvik, Alaska: 30 ounces (852 grams)

In the winter, spring and early summer, adult males are in breeding plumage with a black back, white shoulders, chestnut breast and belly, a white head with a greenish tuft and small black eye patches. During the late summer and fall, males are entirely mottled dark brown. Females and juveniles are mottled dark brown year-round. Adults of both sexes have a blue patch with a white border on the upper wing, similar to mallards.

Not overly vocal, Steller’s eiders make soft guttural croaking and clucking sounds, particularly on the breeding grounds.

Breeding habitat for the Alaska population is closely associated with the polygonal tundra pond environment of the Arctic Coastal Plain of Alaska, with the highest concentration near Utqiagvik. Past breeding has also occurred in coastal wetland areas of the Yukon-Kuksokwim Delta, where nesting is now rare. Molting and wintering areas are typically shallow, near-shore waters of southwest and southcentral Alaska, where the birds mix with other Steller’s eiders that breed in Russia. Steller’s eiders often congregate in lagoons with eelgrass beds present where foraging takes place on associated invertebrates.

The incubation period for Steller's eiders is about 24 days from the last egg laid. The young are precocial and typically depart the nest within 24 hours of hatching. Ducklings are fully capable of walking and swimming from the time they leave the nest but are not fully fledged until about 49 days of age. Steller’s eiders undergo a fall flightless molt in shallow nearshore waters in southwest Alaska. Females reach reproductive age at 2 to 3 years of age.

Steller's eiders are a long-lived sea duck species. The oldest recorded individual in the wild according to banding records was a female that was at least 23 years old.

Males and females form pair bonds during the winter and arrive on the tundra breeding grounds paired. Breeding habitat is typically northern coastal open polygonal tundra in Russia and Alaska. Courtship displays and mating take place as the snow disappears on the tundra and ponds. The female forms a nest bowl on the tundra or short willows and lines it with dark down. Nests are typically near shallow ponds surrounded by grasses or sedges. Clutch size is typically 5 to 8 eggs, and incubation takes place only by the female. Males begin to disperse from breeding areas during incubation and the hen alone raises the ducklings.

Steller’s eiders forage in tundra ponds during the breeding season, feeding on invertebrates like midge and caddisfly larvae. Food consumption during the non-breeding season consists of invertebrates like mussels, clams and crustaceans. Foraging in molting and wintering areas is often associated with eelgrass beds that support a diverse array of marine invertebrates that are consumed.