Steller's Eider vs King Eider

In short

The most reliable field mark between Steller's Eider and King Eider is size: Steller's Eider is much smaller and more compact, with a shorter, stubbier bill and a relatively longer tail. In flight, both species show a distinctive wing pattern, but Steller's Eider (of all ages) has a prominent bluish-purple speculum with long white borders, while King Eider's wing pattern is less striking and lacks the continuous white border. Adult males in breeding plumage are unmistakable, but females and immatures are easily confused; careful attention to structure, wing pattern, and subtle plumage details is essential. Vocalizations and habitat can help, but are less reliable than these visual clues.

Identification tips

1. Size is the first check: Steller's Eider is much smaller and more compact than King Eider. If the bird looks small for an eider, suspect Steller's.
2. Bill shape: Steller's Eider has a shorter, thicker bill with a straight profile; King Eider's bill is longer, sloping, and in adult males, has a large orange/yellow knob at the base (absent in females/immatures).
3. Tail length: Steller's Eider has a relatively longer tail for its body size, often obvious when swimming or in flight.
4. Wing pattern (all ages): In flight, look for the bluish-purple speculum with long white borders on Steller's Eider; King Eider's speculum is less contrasting and lacks the continuous white border.
5. Tertials: Adult male Steller's Eider has long, draped tertials with white stripes; King Eider male's tertials curve up as 'spurs.' Juvenile Steller's Eiders have short tertials.
6. Female/juvenile face pattern: Steller's Eider females and juveniles have a pale eye-ring; King Eider females have a buffy spot at the bill base and a buffy eye-ring with a downward-curving stripe.
7. Male breeding plumage: Steller's Eider male is white-headed with black cap and collar, green patches, and cinnamon breast with a black spot; King Eider male is larger, with a multicolored head, black body, and orange/yellow bill knob.
8. Eclipse males: Steller's Eider males in eclipse are dark brown but keep the white inner forewing; King Eider males lose their bright colors and resemble females.
9. Flight style: Steller's Eider is fast and agile, flying in tight flocks; King Eider is heavier and slower.
10. Leg and foot color: Steller's Eider has dark bluish-grey legs and feet; King Eider's are greenish-grey (females).
11. Habitat context: In Alaska, Steller's Eider is rare and localized, often in dense flocks in lagoons; King Eider is more widespread and often in exposed coastal waters.
12. Vocalizations: Steller's Eider's mechanical wing whistle and low growl may be heard in flight or display, but are rarely diagnostic.
13. Juvenile confusion: Juvenile Steller's Eider is lighter brown with narrow white edges to the speculum; King Eider juveniles are greyish brown, lacking the white-bordered speculum.
14. Group composition: Large, dense flocks in shallow, sheltered waters in Alaska are more likely Steller's Eider, especially outside the main King Eider migration.
15. When in doubt: If only a distant brown eider is seen, prioritize size, bill shape, and wing pattern; if these are ambiguous, identification may remain uncertain.

Size

Steller's Eider is significantly smaller, with an average body mass of about 807 g, compared to the King Eider's 1617 g. In the field, Steller's Eider appears compact, with a relatively large head, short neck, and longer tail for its size, while King Eider is bulkier, longer-bodied, and heavier overall. The difference is especially obvious when both species are seen together, but even singly, Steller's Eider's small, agile appearance stands out among sea ducks.

Plumage

• Juveniles and Females: Steller's Eider juveniles and females are dark to cinnamon brown with a pale eye-ring and a distinctive bluish-purple speculum bordered by white along the full length of the secondaries; tertials are short in juveniles. King Eider females and juveniles are warm brown with blackish chevrons above and fine streaks on the head and neck, a buffy spot at the bill base, and a buffy eye-ring with a downward-curving stripe; their speculum lacks the continuous white border and is less contrasting.
• Adult Males (Breeding): Steller's Eider males have a striking white head with black cap and collar, green patches, cinnamon breast with a black spot, and long, dark tertials with white stripes. King Eider males are larger, with a multicolored head (bluish-grey, green cheek, orange/yellow bill knob), black body, and buff-tinged white breast; tertials curve upward as 'spurs.'
• Eclipse/Non-breeding Males: Steller's Eider males become dark brown like females but retain the white inner forewing, visible in flight. King Eider males in eclipse are less well described but gradually lose their bright colors, resembling females more closely.

Behaviour

Steller's Eider is notably fast and agile in flight, often seen in tight, dense flocks, especially during moult. King Eider is heavier and more ponderous, with a slower, more powerful wingbeat. Steller's Eider's flight is whistling and rapid, while King Eider appears more robust and less maneuverable. Both species dive for food, but Steller's Eider is more likely to be seen in large, synchronized groups during moult.

Habitat

Both species breed in Arctic tundra near water, but Steller's Eider prefers marshy tundra with access to small ponds, while King Eider nests in a wider range of tundra habitats. In winter, both are coastal, but Steller's Eider often forms dense flocks in shallow lagoons and sheltered bays, whereas King Eider is more likely to be found in exposed coastal waters and offshore. Local abundance may differ: in Alaska, Steller's Eider is much rarer and more localized than King Eider.

Voice

Steller's Eider males give a low, jumbled growl and a mechanical whistling sound in flight; females utter a discrete 'qua-haaa.' King Eider vocalizations are not detailed in these notes, but neither species is especially vocal outside courtship. In practice, vocalizations are rarely diagnostic for field separation.