King Eider

King Eiders are seasonally monogamous, forming new pair bonds each year during winter and spring migration. Most pairs are established before or during the northward journey to breeding grounds, with courtship taking place on the water. Several males may court a single female simultaneously, performing elaborate displays: turning the head rapidly from side to side, rearing up out of the water while rotating the head, flapping wings, stretching the neck, and calling softly.

Nest sites are selected by both sexes flying over the tundra together, with the female making the final choice. The nest is a shallow scrape in the ground, typically near a rock, hummock, or ridge, always concealed by low vegetation and close to water. Island nest sites offer considerably higher success rates than mainland sites — 30–89% on islands versus just 0–22% on the mainland (Kellett & Alisauskas 2000) — likely because islands provide better protection from terrestrial predators such as Arctic fox. The female lines the scrape with grasses, sedges, and lichens, adding large amounts of her own down after laying the third or fourth egg; the finished nest averages about 25 cm across (Cramp & Simmons 1977).

Clutch size is typically 4–5 eggs (range 2–7), pale olive or olive-buff in colour, measuring approximately 6.6–7.6 cm × 4.1–4.8 cm (Cramp & Simmons 1977). Incubation is by the female alone for 22–24 days. She sits extraordinarily tightly throughout — one individual was recorded not leaving the nest for seven consecutive days before being flushed by an Arctic fox. The male departs once incubation begins, joining other males at moulting areas at sea. Most females first breed at age three, though some two-year-olds attempt nesting.

Chicks are precocial — covered in down and mobile within hours of hatching — and find all their own food from the outset. Broods frequently merge into crèches accompanied by several adult females, and fledging occurs at approximately 50 days, in saltwater. King Eiders do not renest if a clutch is lost; the Arctic summer is simply too short. The breeding season runs from late June to early July across most of the range.

King Eiders are relatively long-lived for ducks, with a typical lifespan of 10–18 years in the wild. The maximum recorded age is 24 years, set by a male with an exceptional history: rescued after an oil spill in the Pribilof Islands, Alaska in 1996, banded during rehabilitation by International Bird Rescue, and re-encountered alive in 2019 — 23 years after his treatment. His survival is both a longevity record and a data point for the effectiveness of oiled-bird rehabilitation programmes.

Survival rates vary considerably with age and season. First-year birds face the highest mortality, with inexperienced juveniles vulnerable to predation, starvation during their first Arctic winter, and the physical demands of their first long-distance migration. Adults that survive to breeding age benefit from accumulated experience in finding food and avoiding predators, which is reflected in the relatively high upper end of the lifespan range.

The main natural mortality causes include predation (glaucous gull, Arctic fox, and parasitic jaeger take eggs and chicks; large raptors occasionally take adults), starvation during severe winters when sea ice restricts access to foraging areas, and the physical toll of long-distance migration. Human-related mortality includes subsistence and sport hunting, bycatch in fishing nets, and mortality from oil spills. Compared to the closely related Common Eider, which has a similar maximum lifespan, King Eiders face additional pressure from their more remote and climatically extreme wintering grounds.

The King Eider is listed as Least Concern on the IUCN Red List — but that designation sits uneasily alongside a very different assessment from North American monitoring programmes. The 2025 State of the Birds report classifies the species as an Orange Alert Tipping Point bird, meaning it has lost more than 50% of its population over the past 50 years and has shown accelerated declines within the past decade. Spring migration counts at Point Barrow, Alaska — the most reliable long-term index of population size — showed declines of more than 50% between 1976 and 1996, though counts between 1994 and 2016 suggest the population has since stabilised or even partially recovered. Partners in Flight rates the species 15 out of 20 on the Continental Concern Score.

Global population estimates vary considerably by source and methodology. BirdLife International and the IUCN estimated 800,000–900,000 mature individuals in their 2018 assessment; Partners in Flight puts the global breeding population at over 830,000; Ducks Unlimited cites a broader figure of 1.5–3 million total birds, with 1–2 million in North America. Both the Pacific and Atlantic North American subpopulations are considered to be declining.

Climate change is the chief long-term threat, already altering sea ice extent and timing, changing prey availability, and modifying tundra breeding habitats. Oil and gas development and oil spills pose acute risks, particularly in the Bering Sea and other key wintering areas.

Subsistence and sport hunting is substantial: an estimated 20,000 King Eiders are harvested annually in Alaska and Canada alone, with tens of thousands more taken in Greenland and Russia. The species is also subject to bycatch in fishing nets. The King Eider is listed under the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA), which requires range states to coordinate management plans, protect key staging and wintering sites, and regulate harvest levels across national boundaries.

King Eider courtship is a prolonged affair, beginning on wintering grounds in late winter and continuing through spring migration. Several males typically court a single female simultaneously, competing through a series of ritualised water displays rather than outright aggression. The male's repertoire includes rapid side-to-side head turns, rearing up out of the water while rotating the head, neck stretching, wing flapping, and the soft cooing call — a combination that shows off the frontal knob, iridescent cheeks, and "sail" feathers to maximum effect.

Females are not passive participants. A receptive female responds by dipping her bill to the water surface, bathing, preening, and flapping her wings — signals that encourage the male to intensify his display. Pair bonds are formed gradually over weeks of repeated interaction, with the female ultimately selecting her mate from among the competing males. Once a pair bond is established, the male guards his mate closely during the journey to breeding grounds and through the egg-laying period, driving off rival males with threat postures.

The male's frontal knob — the yellow-orange shield above the bill — is thought to function as a sexual ornament, with larger, more brightly coloured knobs potentially signalling male quality. The knob grows and brightens as males approach breeding condition, then shrinks and fades during eclipse moult. Both sexes may give displays that superficially resemble courtship postures in aggressive contexts, which can make field interpretation challenging without careful attention to the social setting.

The King Eider has been woven into the culture of Arctic peoples for thousands of years. Among the Yup'ik of western Alaska, the bird is known as qengallek — a name that reflects the frontal knob, or "nose". King Eiders and other eiders have historically provided food (meat and eggs), warm clothing (the dense down is among the finest natural insulation known), and materials for tools and decoration.

Subsistence harvest of King Eiders continues today across Alaska, Canada, Greenland, and Russia, where the species has been hunted by Inuit and other indigenous communities for generations. This harvest remains an important part of food security and cultural practice in remote Arctic communities, though its scale — and the species' declining population — has brought it into focus for conservation managers.

The species also holds a place in the history of natural history illustration. John James Audubon painted the King Eider for The Birds of America, and the male's extraordinary plumage has made it a recurring subject for wildlife artists and photographers. The frontal knob and "sail" feathers have no close parallel in any other duck, making the species a favourite among collectors of taxidermy and natural history specimens — a popularity that contributed to historic hunting pressure before legal protections were established.

In contemporary conservation culture, the King Eider's migration past Point Barrow has become something of a pilgrimage for serious waterfowl enthusiasts. The spectacle of hundreds of thousands of birds streaming north over the Arctic Ocean in May draws observers from around the world to the remote community of Utqiaġvik (formerly Barrow), the northernmost city in the United States.