Steller's eider (Polysticta stelleri) is a migratory Arctic sea duck that breeds along the coastlines of Russia and Alaska, as well as in the Baltic Sea. It is the smallest, and fastest flying of the duck species known as eiders; it is closely related to the other species of eider in the genus Somateria, but sufficiently distinct to be given separate recognition as the only member of the genus Polysticta. Due to the extensive contraction of its breeding range, the Alaska-breeding population of Steller's eider was listed as vulnerable in 1997 by the International Union for the Conservation of Nature (IUCN). The species is protected in Estonia, Finland, Norway, Russia and the United States, and is the subject of an ongoing recovery plan by the European Union and U.S. Fish and Wildlife Service.
Taxonomy Steller's eider was formally described and illustrated in 1769 by the German naturalist Peter Simon Pallas from a specimen collected on the Kamchatka Peninsula in Eastern Russia. He coined the binomial name Anas stelleri; the specific epithet was chosen to honour the German naturalist and explorer Georg Wilhelm Steller. Steller's eider is now the only species placed in the genus Polysticta that was introduced in 1836 by the English naturalist Thomas Eyton. The species is monotypic, with no subspecies being recognised. The genus name is from Ancient Greek polustiktos meaning "much spotted" (from polus "many" and stiktos "spotted"). Steller's eider was separated from the other eider species into its own genus in 1945 due to behavioural and anatomical differences. Genetically, it is however closely related to all other extant eider species in the genus Somateria. Its closest relative was the now-extinct Labrador duck Camptorhynchus labradorius, but with these two species next closest to the genus Somateria; the genetic divide of these two from Somateria is only marginally larger than the genetic variation within the genus Melanitta.
Description
Steller's eider is the smallest of the four eiders, with both females and males weighing 860 g (30 oz) on average. They have a compact body with a relatively large head with a flat crown and an angled nape, and a long, thick bill; the tail is relatively longer than other eiders. The males assume their breeding plumage from early winter to midsummer with a black cap, chin, collar, eye-ring, and rump, with a white head and shoulders, light green patches behind the head and in front of the eye, and the cinnamon breast and shoulders marked with a prominent black spot. The tertial feathers are long, draped over the folded wing, dark purple-black, with a while stripe along each. In mid-summer to autumn, males assume their 'eclipse' (non-breeding) plumage, which is primarily dark brown like females, but retaining the white inner forewing, conspicuous in flight. Both sexes have an iridescent bluish-purple speculum on the secondary feathers on their wing, with white borders running the entire length of the secondaries. Females are dark to cinnamon brown, with a pale-white eye-ring; the juveniles are similar, but lighter brown, and with only narrow white edges to the speculum and short tertial feathers. The feet are palmate, with three fully webbed toes, dark bluish-grey, with the legs the same colour.
Habitat and distribution During the winter, Steller's eiders occupy coastal bays and lagoons that offer suitable forage while occasionally feeding in deeper waters that remain adequately sheltered. They nest in marshy tundra along the coast, in areas dominated by water sedge and pendant grass. Within the marshy tundra, they designate specific areas to build their nest, preferring elevated surfaces covered by shallow vegetation such as mosses and grasses. Their moulting habitat consists of relatively shallow coastal lagoons that offer viable eelgrass and tidal flats for foraging and beaches and sandbars to rest while they remain flightless.
Population distributions There are three recognised breeding populations of Steller's eiders, one in Alaska and two in Arctic Russia.
The Russian-Atlantic population breeds west of the Khatanga River in western Siberia, and winters in the Barents and Baltic seas. The Russian-Pacific population breeds east of the Khatanga River, and winters in the southern Bering Sea and northern Pacific Ocean. The Alaska-breeding population nests on the Arctic Coastal Plain and in exceptionally small numbers in the Yukon–Kuskokwim Delta, and winters in the southern Bering Sea and northern Pacific ocean. Less than 1% of the world's Steller's eiders nest in Alaska. Some non-breeding populations will also spend their summers in northern Norway, on the east coast of Russia and adjacent waters, and south-west Alaska.
Behaviour and ecology
Diet
Steller's eiders forage primarily near the shore by employing various techniques such as briefly diving and swimming underwater (to a maximum depth of 9 m), wading and dabbling. They feed by surface techniques more than other sea ducks and prefer relatively small prey. Studies have shown that Steller's eiders are specialists in catching highly mobile prey but may limit their diet to crustaceans even when higher energy sources, such as capelin, become available. This discrepancy in food preferences may be due to their inability to exploit deeper habitats. Steller's eiders also feed on molluscs, echinoderms, polychaete worms, and mussels during the winter. While in the tundra during the summer months, they feed on aquatic insects and plant material such as crowberries and pondweeds.
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