Steller's sea eagle is a large magnificent bird of prey named after the German naturalist Georg Wilhelm Steller. On average, it is the heaviest eagle in the world. It has dark brown plumage with white wings and tail, and yellow beak and talons. This impressive and fierce hunter lives in coastal northeastern Asia and mainly preys on fish and water birds.
Steller's sea eagles breed on the Kamchatka Peninsula, the coastal area around the Sea of Okhotsk, the lower reaches of the Amur River, and on northern Sakhalin and the Shantar Islands, Russia. The majority of birds winter south of their breeding range, in the southern Kuril Islands, Russia, and Hokkaidō, Japan. Some eagles, especially those that nest in the seacoast, may not migrate. Steller's sea eagles prefer habitats with large Erman's birches and floodplain forests of larches, alders, willows, and poplar. On Kamchatka, they overwinter in forests and river valleys near the coast but are irregularly distributed over the peninsula. Eagles that do migrate fly down to winter in rivers and wetlands in Japan, but will occasionally move to mountainous inland areas as opposed to the sea coast. Each winter, drifting ice on the Sea of Okhotsk drives thousands of eagles south. They may also occasionally fly over the northern ocean or perch on sea ice during the winter.
Steller's sea eagles are generally solitary and spend much of their time soaring or perched on sea cliffs or trees looking for prey. They hunt by day most commonly from a perch in a tree or rocky ledge located 5-30 m (16-98 ft) above the water; they may also hunt on the wing while circling 6-7 m (20-23 ft) above the water. Once located, the prey is captured by diving. Eagles sometimes hunt by standing in or near shallow water on a sandbank, spit, or ice-flow, grabbing passing fish. Relatively large numbers of these birds may gather in flocks on particularly productive spawning rivers in August through September due to an abundant food supply. Outside the breeding period, they often roost communally near their feeding sites. When salmon and trout are dying in winter after their summer spawning, feeding groups of Steller's sea eagles may mix with smaller Golden eagles and White-tailed eagles to exploit the food source. The timing, duration, and extent of Steller's sea eagles' migration usually depends on ice conditions and food availability. The birds depart between late March and late April, adults typically leaving before immatures. Migrants tend to follow sea coasts and usually fly singly. When in groups, migrants typically fly 100-200 m (330-660 ft) apart. Steller's sea eagles communicate with each other using a call similar to the White-tailed eagles but deeper and also make a deep barking cry, ra-ra-ra-raurau, in aggressive interactions. During the breeding season, they make calls that sound like very loud, deep-voiced gulls.
Steller's sea eagles are monogamous and form long-lasting pair bonds. Courtship usually occurs between February and March and consists of a soaring flight above the breeding area. These birds nest on large rocky outcroppings or at the tops of large trees on the coast and alongside large rivers with mature trees. A pair builds several aeries (nests) but only one nest is used for raising chicks. The nest itself is a bulky construction of twigs and sticks, at a height up to 150 cm (59 in) and diameter up to 250 cm (98 in). The female lays her greenish-white eggs around April to May. Clutches can contain from 1 to 3 eggs, with 2 being the average. Usually, only one chick survives to adulthood, though in some cases as many as three will successfully fledge. After an incubation period of around 39-45 days the chicks hatch. They are altricial and covered in whitish-down on hatching. The eaglets fledge in August or early September. Adult plumage is attained at 4 years of age, but first breeding does not typically occur for another year or two.
The main threats to these rare sea eagles include habitat alteration, industrial pollution, and overfishing, which in turn decrease their prey source. It was observed that recent heavy flooding, which may have been an effect of global climate change, caused almost complete nesting failure for the eagles nesting in Russian rivers due to completely hampering the ability of the parents to capture the fish essential to their nestlings' survival. Persecution of the bird in Russia continues, due to its habit of stealing furbearers from trappers. Due to a lack of other accessible prey in some areas, increasingly, eagles on Hokkaido have moved inland and scavenged on Sika deer carcasses left by hunters, exposing them to a risk of lead poisoning through ingestion of lead shot.
According to the IUCN Red List, the total population size of Steller's sea eagle is around 4,600-5,100 individuals, including around 1,830-1,900 breeding pairs. Currently, this species is classified as Vulnerable (VU) on the IUCN Red List and its numbers today are decreasing.