The Steller's sea eagle is endemic to coastal northeastern Asia, where it lives in Russia, Korea, Japan, China, and Taiwan.

Last seen in 1968 and long believed to be extinct, a female matching H. p. niger in appearance was hatched in captivity in the Bayerischen Jagdfalkenhof (Germany) in 2001 and subsequently transferred to Tierpark Berlin.

Both her parents had typical coloration, indicating that H. p. niger is an extremely rare dark morph rather than a valid subspecies, as had been suggested earlier.

[35] The bold, pied coloration of adults may play some part in social hierarchies with other eagles of their own species during the nonbreeding season, although this has not been extensively studied.

[4][30] A very rare dark morph, once regarded as a separate subspecies, H. p. niger, lacks white in its plumage, except for the tail.

Juvenile plumage is largely a uniform dark soot-brown with occasional grey-brown streaking about the head and the neck, white feather bases, and light mottling on the rectrices.

Through at least three intermediate plumages, mottling in the tail decreases, body and wing feathering acquires a bronze cast, and the eyes and bill lighten in colour.

[30][41] The large body size (see also Bergmann's rule) and distribution of Steller's sea eagle suggests it is a glacial relict, meaning it evolved in a narrow subarctic zone of the northeasternmost Asian coasts, which shifted its latitude according to ice age cycles, and never occurred anywhere else.

Habitat with large Erman's birches (Betula ermanii) and floodplain forests of larches, alders, willows, and poplars are preferred.

Steller's sea eagles that do migrate fly south to winter in rivers and wetlands in Japan, but occasionally move to mountainous inland areas as opposed to the seacoast.

[45] Subsequently, a Steller's sea eagle was photographed in Victoria, TX, not long after a winter storm blew into the state.

This sighting has been verified by the Texas Bird Records Committee and is presumed to be the same individual as seen in Denali, though the photos are not sufficient to establish this identity.

In December, it was spotted on the Taunton River in Massachusetts and then moved north to the Maine coast (Georgetown, Boothbay, and Pemaquid).

[32] In coastal areas, nesting eagles may feed on Bering wolffish (Anarchichas orientalis), Hemitripterus villosus, smooth lumpfish (Aptocyclus ventricosus), and Myoxocephalus spp.

Relatively large numbers of these normally solitary birds can be seen congregating on particularly productive spawning rivers in August through September due to an abundant food supply.

In autumn, when many salmon die after spawning, dead fish tend to be consumed more often than live ones, and these are the main food for Steller's sea eagles that overwinter in inland rivers with unfrozen waters.

[30] On Hokkaido, eagles are attracted by abundant Pacific cod (Gadus macrocephalus), which peak in the Rausu Sea and the Nemuro Straits in February.

[55] Common and thick-billed murres (Uria aalge and U. lomvia, respectively) dominated the diet around the Sea of Okhotsk, followed by black-legged kittiwakes (Rissa tridactyla), slaty-backed gulls, crested auklets (Aethia cristatella), and pelagic cormorants (Phalacrocorax pelagicus).

[54] In one case, a Steller's sea eagle was observed feeding on a great albatross (genus Diomedea), a rare vagrant from the sub-Antarctic oceans.

[4] This sea eagle may supplement its diet with various mammals (especially hares[4][30]), crabs, mussels, Nereis worms, and squid when given the opportunity.

Around 35% of eagles wintering in Japan move inland and feed largely on mammalian carcasses, predominantly sika deer (Cervus nippon).

It was estimated in one study (Brown & Amadon), that some seal pups carried off in flight by the eagles weighed at least 9.1 kg (20 lb), which (if true) would be the greatest load-carrying ever known for a bird; however, the prey weights were not verified.

However, a video from Russia shows a juvenile Steller's sea eagle aggressively displacing an adult from food during a protracted battle.

One video shows a golden eagle engaging an immature Steller's in a conflict and ultimately displacing it after maintaining a superior grip despite its smaller size.

[62] In other cases, the Steller's have been photographed coming away with the prey after using its superior size to dominate, usually by bearing down its mass and large bill over the smaller eagles.

[66] Steller's sea eagles co-occur with cinereous vultures, the largest living accipitrid, during the winter in the Korean Peninsula and Northeast China.

In one case, a cinereous vulture, the largest living accipitrid, was observed to be pursued in flight and kleptoparasitized by a Steller's sea eagle.

This can be a clue to occasional polygamy in colonial nesting birds, though alternative hypotheses such as the parents of “conditional” siblings were close relatives exist.

In one case, a brown bear (Ursus arctos) was able to access a nest located on a rock formation and ate a fledgling eaglet, though this is believed to be exceptional.

Excluding the Asian black bear (Ursus thibetanus), which has not thus far been recorded as a predator, no other mammalian carnivores equal to or greater than the eagle's size can climb trees in the species' range.