Of all the ducks that reach the far north, the one that best symbolizes the Arctic is the King Eider. This hardy duck breeds on tundra along some of the northernmost shorelines in the world, including Arctic Russia, the northernmost Canadian islands, and the north coast of Greenland. Even in winter, it’s a northern species; North American populations spend the winter mostly in southern Alaska and along the coast of eastern Canada. However, small numbers come as far south as our middle Atlantic Coast and the Great Lakes in winter, and strays have appeared much farther south, so birders everywhere have reason to be aware of this species.
Many ducks show strong sexual dimorphism — that is, obvious visible differences between females and males: The females wear cryptic camouflage while the males show off with conspicuous bright colors. Eiders are extreme examples of this. The full adult male King Eider wears breeding plumage from late fall to early summer, and it’s an unbelievably gorgeous bird. However, females, young males, and adult males in the late summer “eclipse” plumage are subtler, requiring closer study.
Travelers in the Arctic may see flocks of hundreds of King Eiders at certain favored spots. But in winter in southeastern Canada and the northeastern United States, most sightings are of single individuals or very small numbers, mixed in with larger flocks of Common Eiders. The majority of these Kings, especially at more southerly latitudes, are females or young males, not adult males, creating a challenge for observers.
In teaching bird-ID workshops, I’ve often made the point that most North American ducks can be identified by head shape and bill shape. This is true of King Eider, but we have to note that these points vary with the age and sex of the bird. Brian Small’s photos in this column demonstrate the point well. Females show the same squarish head shape and relatively small bill at all ages, but on males, a knob at the base of the bill gets gradually larger as they approach full adulthood at about three years of age; even as adults, this forehead bulge is most pronounced in breeding season, reduced in late summer and early fall.
What to look for
Size and shape. A large, heavy-bodied, short-necked duck, smaller than Common Eider but larger than most other ducks.
Head shape. Blocky, squarish head with relatively short bill. Males have swollen knob on forehead, more pronounced on breeding adults, and females may show hint of same.
Female color pattern. Dark brown overall with heavy barring and mottling. Sides and flanks marked with black scallops or chevrons, not vertical bars.
First winter male pattern. Mostly dark brown with variable white on chest, orange at base of bill. Usually no white on back.
Female Common Eiders vary in tone from grayish to warm cinnamon to dark brown, so overall plumage color isn’t very useful in separating them from female King Eiders. Structure and pattern are better clues. The slightly larger size of Common Eider isn’t obvious without a direct comparison, but Common has a more long-bodied look. Its head is angular with a high peak at the front of the crown, leading into a long, sloping forehead and long bill. A lobe of feathering extends forward on the side of the bill, reaching the nostril. Feather patterns are less obvious, but the Common shows vertical barring on the sides and flanks, unlike the deeper scallops or chevrons on the female King Eider.
The full adult male King Eider wears its ornate breeding plumage from late fall to early summer. Like other ducks, it molts into a subtler “eclipse” plumage for a time in late summer and early fall. On this June bird in full breeding plumage, notice the points sticking up from the back; these modified scapular feathers serve only as decoration. The hugely swollen knob at the base of the bill is also a decorative touch, reduced in size when the bird is not in breeding plumage. Male King Eiders have been observed several times displaying to, and mating with, female Common Eiders. The opposite pairing — male Common with female King — seems to be far less likely.
Male King Eiders may take three years, or even four, to reach full adult plumage. After their first year, they look enough like adults to be recognizable. However, first-winter males are subtler. Typically, they are dark with white on the chest, but the same is true for male Common Eiders of the same age. Head shape and bill shape are important for distinguishing them. On the young male King Eider, the swelling at the base of the bill and the yellow-orange color on the bill may become more obvious later in the winter, as seen on this March bird. The feathering on the side of the bill doesn’t extend nearly as far forward as on Common Eider.
Winter flocks of Common Eiders are usually a mix of brown females, crisp black and white adult males, and patchy young males. The young males are most readily separated from young male Kings by head and bill structure. The long, sloping forehead leading smoothly into the long bill creates a profile unlike that of any other duck; only the Canvasback and Spectacled Eider come close. The feathering around the bill helps to emphasize the unique shape, with a bare unfeathered lobe reaching up the forehead and feathers extending halfway out the side of the bill. For an additional plumage point, most first-winter male Commons have some white on the back, usually lacking on first-winter male Kings.
A tale of two eiders
King Eider and Common Eider are considered to be each other’s closest relatives, with Spectacled Eider and Steller’s Eider a little more distantly related. King and Common Eiders are widespread at northern latitudes, and they overlap extensively in range, but there are intriguing differences between them.
There’s a strong contrast in their amount of geographic variation. Common Eider has been separated into six or seven subspecies, and some differences among them are obvious. For example, females from Hudson Bay are pale and gray, while those along the east coast of Canada are more reddish brown. Adult males have greenish gray bills in eastern Canada, orange bills in Alaska.
By comparison, no subspecies of King Eider are recognized. They look the same throughout their range. Why the difference? Apparently, it’s caused by their migratory strategies. Some populations of Common Eiders are year-round residents, and most others migrate only short distances. This creates some isolation, making it possible for distinct forms to evolve over time. King Eiders are much more migratory, departing from all breeding areas in winter, some traveling thousands of miles. Pairs form on the wintering grounds or during spring migration. Females return to the same general breeding areas every year, but males simply follow their mates and may wind up in very different places from one year to the next. The result is a constant mixing of genes throughout the species as a whole.