The Common Eider (Somateria mollissima) is a large sea duck that breeds in Arctic and some northern temperate regions. There are four recognized subspecies of Common Eiders that vary slightly in appearance and range:
Northern Common Eider (Somateria mollissima borealis)
The Northern Common Eider is the nominate subspecies and the most numerous of the Common Eiders. It breeds across Arctic regions of North America, Greenland, Iceland, Scandinavia, and Russia. The Northern Common Eider winters south to New England in the United States and northern Europe.
Male Northern Common Eiders have black caps, green neck patches, white backs, black bellies and tails, and a light peach colored chest. Females are mottled brown in color. Northern Common Eiders grow to about 24-28 inches in length. They eat mollusks, crustaceans, and other small invertebrates and nest on the ground along rocky coasts and islands.
Key Characteristics:
- Breeds across the Arctic
- Winters south to New England and northern Europe
- Males have black and white plumage with green neck patches
- Grows to 24-28 inches
Pacific Common Eider (Somateria mollissima v-nigrum)
The Pacific Common Eider breeds and winters along the northern Pacific coasts of North America and Asia. In North America, it ranges from Alaska to northern California. In Asia, it breeds across northern Russia and winters south to Japan and northern China.
Compared to other Common Eiders, the Pacific Common Eider is darker in color. Males have a darker cap and green coloration extending further down the nape and chest. Females are very dark brown. Pacific Common Eiders are mid-sized for the species at about 22-26 inches in length.
Key Characteristics:
- Found along the northern Pacific coast
- Darker plumage compared to other subspecies
- Green color extends further down on males
- Females very dark brown
- Grows to 22-26 inches
European Common Eider (Somateria mollissima mollissima)
As the name suggests, the European Common Eider is found in Europe, breeding from Iceland and northern Scotland east to Scandinavia and the Baltic regions. It winters south along the coasts of northern Europe. Though similar in appearance to the Northern Common Eider, the European Common Eider averages slightly smaller in size.
Males have a pale green head patch that contrasts with a black cap. Their bodies are boldly patterned in black and white. Females are a cryptically patterned brown. European Common Eiders grow to about 22-25 inches long and dine on bivalves, gastropods, and crustaceans.
Key Characteristics:
- Found along coasts of northern Europe
- Males have pale green head patches
- High contrast black and white body plumage
- Females mottled brown
- Grows to 22-25 inches
Hudson Bay Common Eider (Somateria mollissima sedentaria)
The Hudson Bay Common Eider is a small subspecies that breeds along the coasts of Hudson Bay and winters south into the Great Lakes region. It is similar in appearance to the Northern Common Eider but is the smallest of the four subspecies. Hudson Bay Common Eiders reach about 20-24 inches in length.
Males have extensive black bellies and lighter peach coloring on the chest compared to other subspecies. Females are brown but paler than Pacific females. The Hudson Bay Common Eider frequents rocky coasts and shoals, feeding on mollusks and other invertebrates.
Key Characteristics:
- Breeds along Hudson Bay
- Winters south into the Great Lakes
- Small in size at 20-24 inches
- Males have extensive black bellies
- Females are pale brown
Comparison of Common Eider Subspecies
While the four Common Eider subspecies vary in range and appearance, they share many common traits. Some key similarities and differences are summarized in the table below:
| Subspecies | Range | Male Plumage | Female Plumage | Size |
|---|---|---|---|---|
| Northern | Arctic coasts | Black cap, white back, green patch | Mottled brown | 24-28 in |
| Pacific | Northern Pacific coast | Dark cap, green extends down chest | Very dark brown | 22-26 in |
| European | Northern Europe | Pale green patch, high contrast plumage | Mottled brown | 22-25 in |
| Hudson Bay | Hudson Bay | Extensive black belly | Pale brown | 20-24 in |
Conclusion
In summary, the four subspecies of the Common Eider sea duck are:
- Northern Common Eider – Arctic regions
- Pacific Common Eider – Northern Pacific Coast
- European Common Eider – Northern Europe
- Hudson Bay Common Eider – Hudson Bay
While they occupy different ranges, the subspecies share similarities like their mollusk-based diets and ground nesting habits. They can be distinguished by small variations in size, male plumage patterns, and female coloration. Understanding these differences allows researchers and birders to better identify Common Eider subspecies across their broad northern range.
