Steller's Sea-Eagle

Identification

Steller's sea eagle is the largest bird in the genus Haliaeetus and is one of the largest raptors overall. Females vary in weight from 6.2 to 9.5 kg (14 to 21 lb), while males are rather lighter with a weight range of 4.9 to 6.8 kg (11 to 15 lb). The typical weight is variable, possibly due to seasonal variation in food access or general condition of eagles, but has been reported as high as a mean weight of 7.75 kg (17.1 lb) to a median estimate weight of 6.25 kg (13.8 lb), excluding expired eagles that were poisoned by lead and endured precipitous weight loss by the occasion of their deaths.<p>At its average weight, the Steller's seems to outweigh the average harpy by around 0.5 kg (1.1 lb) and the average Philippine eagles by more than 1 kg (2.2 lb). Steller's sea eagle can range in total length from 85 to 105 cm (2 ft 9 in to 3 ft 5 in). Apparently, males average about 89 cm (2 ft 11 in) in length, while females average about 100 cm (3 ft 3 in), marginally shorter on average than the harpy eagle and about 65 mm (2.6 in) shorter than the Philippine eagle.<p>The wingspan is from 1.95 to 2.50 m (6 ft 5 in to 8 ft 2 in) and the wing chord measurement is 560 to 680 mm (22 to 27 in). The sea eagle's wingspan is one of the largest of any living eagle, at a median of 2.13 m (7 ft 0 in) per Ferguson-Lees (2001) or a median of 2.2 m (7 ft 3 in) per Saito (2009). Steller's sea eagles' absolute maximum wingspan is less certain; many sources place it at up to 2.45 m (8 ft 2 in). However, less substantiated records indicate that it may also reach even greater wingspans. Three separate sources claim unverified Steller's sea eagles spanning up to 2.7 m (8 ft 10 in), 2.74 m (9 ft 0 in), and 2.8 m (9 ft 2 in), respectively. If true, this would be the largest wingspan of any eagle.<p>Steller's sea eagle is unique among all sea eagles in having a yellow beak even in juvenile birds, and possessing 14, not 12, rectrices.<p>As in most Haliaeetus eagles, the tarsus and tail are relatively short compared to other very large eagles at 95–100 mm (3.7–3.9 in) and 320–390 mm (13–15 in) in length, respectively, with the Philippine eagle surpassing it by up to 40 mm (1.6 in) and 110 mm (4.3 in), apparently. In all sea and fish eagles, the toes are relatively short and stout, with the bottom of the foot covered in spicules and the talons being relatively shorter and more strongly curved than in comparably sized eagles of forests and fields, such as the "booted eagle" group (i.e. Aquila) or "harpy eagles". All of these specializations developed in the aid of capturing fish rather than medium-sized mammals and large birds, although, clearly these are not excluded from capture.<p>As in all fish and sea eagles, as well as the majority of the world's fish-eating raptors, Steller's sea eagle has spicules, which are bumpy waves all along the bottom of their feet, which allow them to hold fish that may otherwise slip out of their grasp. The feet are very powerful despite not bearing talons as long as those of a harpy eagle. In one case, a wildlife veterinarian was badly injured when a female eagle grabbed his arm and embedded her talons, piercing through to the other side of his arm.<p>The bill is large. The skull is around 14.6 cm (5.7 in) in total length, the culmen is from 62 to 75 mm (2.4 to 3.0 in), and the bill from the gape to the tip is around 117 mm (4.6 in). A Steller's sea eagle's bill is probably the largest of any living eagle, just surpassing the Philippine eagle with a sole known culmen measurement (from a mature female) of 72.2 mm (2.84 in), and are similar in robustness (if slightly shorter in culmen length) to those of the largest accipitrids, the Old World vultures.<p>Mature H. pelagicus eagles have mostly dark brown to black plumage, with strongly contrasting white on the lesser and median upper-wing coverts, under-wing coverts, thighs, under-tail coverts, and tail. Their diamond-shaped, white tails are relatively longer than those of the white-tailed eagle. 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. A very rare dark morph, once regarded as a separate subspecies, H. p. niger, lacks white in its plumage, except for the tail. The eyes, bill, and feet of adults are yellow.<p>The downy plumage of chicks is silky white on hatching, though it soon turns a smoky brown-grey. As in other sea eagles, remiges and rectrices of the first-year plumage are longer than those of adults. 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. The tail of the immature eagle is white with black mottling distally. The young Steller's sea eagle has dark brown irises, whitish legs, and blackish-brown beak. 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. Definitive plumage is probably reached in the fourth to fifth year of life, based on data from captives. Young of the typical morph and the rare dark morph are alike. The difference only becomes clear once they have gained the adult plumage.<p>First and intermediate plumages are difficult to distinguish from those of the white-tailed eagle, which co-occurs in the entire breeding range of H. pelagicus, but beyond their bulkier, larger overall form, they can fairly reliably be distinguished at reasonable range by their considerably more massive bill and their darker and more uniform body plumage. This is not to mention the differing shape of the Steller's diamond-shaped tail and wings (paddle-like in Steller's against the square-looking wings of the white-tailed), especially in flight, as well as a generally distinct under-wing pattern.<p>Steller's sea eagle is known to make a deep barking cry, ra-ra-ra-raurau. In aggressive interactions, its call similar to the white-tailed eagles, but deeper. During the display at the beginning of the breeding season, they have been heard to make calls to each that sound like very loud, deep-voiced gulls.

Taxonomy

This species was described initially as Aquila pelagica by Prussian naturalist Peter Simon Pallas, in 1811. The species name is the Ancient Greek pelagos, "the open sea/ocean". Dutch naturalist Coenraad Jacob Temminck named it Falco leucopterus, "white winged eagle", in 1824, and Heinrich von Kittlitz called it Falco imperator in 1832. George Robert Gray moved the species into the genus Haliaeetus in 1849.<p>"Steller's sea eagle" has been designated the official name by the International Ornithologists' Union (IOU). It is named after the German naturalist, Georg Wilhelm Steller. It also is known as Steller's fish eagle, Pacific sea eagle, or white-shouldered eagle. In Russian, the eagle has been called morskoi orel (sea eagle), pestryi morskoi orel (mottled sea eagle), or beloplechii orlan (white-shouldered eagle). In Japanese, it is called ō-washi (large eagle or great eagle). In Korean, the eagle is called chamsuri (true eagle). In Mandarin, it is called hǔtóu hǎidiāo (tiger-headed sea eagle).<p>A 1996 analysis of the cytochrome b gene of mitochondrial DNA showed that Steller's sea eagles diverged from a lineage that gave rise to the bald eagle and white-tailed eagle around 3-4 million years ago. All three of these species have yellow eyes, beaks, and talons, unlike their next-closest relative, Pallas's fish eagle.<p>H. pelagicus is monotypic, although a dubious subspecies has been named; H. p. niger. The latter name was given to the population that lacked white feathers except for the tail, and may have resided all year in Korea. 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. One of the offspring of the dark Berlin female, a male hatched in 2014 that now lives in Skandinavisk Dyrepark (Denmark), also is a dark morph.

Scientific name

Haliaeetus pelagicus

Authority

(Pallas, 1811)

Order

Accipitriformes

Family

Accipitridae

Genus

Haliaeetus

Range and habitat

Steller's sea eagle breeds 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. Many eagles migrate from breeding grounds to Korea, Japan, and China in winter. Most birds winter south of their breeding range, in the southern Kuril Islands, Russia, and Hokkaidō, Japan. Steller's sea eagle is less prone to vagrancy than the white-tailed eagle, as it lacks the long-range dispersal typical of juveniles of that species, but vagrant eagles have been found in North America at locations including the Pribilof Islands and Kodiak Island, as well as Texas, Nova Scotia, Massachusetts, Maine, and Newfoundland (the latter five all being a single individual) and inland in Asia to as far as Beijing in China and Yakutsk in Russia's Sakha Republic, and south to as far as Taiwan.<p>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. Their nests are built on large, rocky outcroppings or at the tops of large trees on the coast and alongside large rivers with mature trees. Habitat with large Erman's birches (Betula ermanii) and floodplain forests of larches, alders, willows, and poplars are preferred. Some eagles, especially those that nest on seacoasts, may not migrate. The timing, duration, and extent of migration depends on ice conditions and food availability.<p>On Kamchatka, eagles overwinter in forests and river valleys near the coast, but are irregularly distributed over the peninsula. Most wintering birds there appear to be residential adults. 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. Each winter, drifting ice on the Sea of Okhotsk drives thousands of eagles south. Ice reaches Hokkaido in late January.<p>Eagle numbers peak in the Nemuro Strait in late February. On Hokkaido, eagles concentrate in coastal areas and on lakes near the coast, along with substantial numbers of white-tailed eagles. Eagles depart between late March and late April, with adults typically leaving before immatures. Migrants tend to follow seacoasts and are usually observed flying singly. In groups, migrants are typically observed flying 100–200 m (330–660 ft) apart. On Kamchatka, most migrants are birds in transitional plumages. They are also occasionally seen flying over the northern ocean or perching on sea ice during the winter.<p>Steller's Sea eagle occasionally turns up in western Alaska. In December 2021, for the first time, one had been documented in the lower 48 states, first on the Taunton River in Massachusetts and then in Georgetown, Maine.

Migration

Complete migrants

Conservation

Steller's sea eagles are classified as vulnerable by the IUCN. They are legally protected, being classified as a national treasure in Japan and mostly occurring in protected areas in Russia, but many threats to their survival persist. These mainly include habitat alteration, industrial pollution, and overfishing, which in turn decrease their prey source. The current population is estimated at 5,000 and decreasing. 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.<p>In Kamchatka, 320 pairs have been recorded. An additional 89 nesting areas are not monitored. In the mountains of Koryakan and along the Bay of Penshina, over 1,200 pairs breed and at least 1,400 juveniles occur. About 500 pairs live in the Khabarovsk region of the Okhostsk coast, and 100 on the Shantar Islands. Another 600 pairs occur in the lower Amur. About 280 pairs are on Sakhalin Island and a few are on the Kurile Islands. The total population is around 3,200 breeding pairs. Possibly, up to 3,500 birds winter on Kamchatka, and another roughly 2,000 may occur on Hokkaido. Generally, the species' outlook is favorable. Outside the breeding range, food bases in the principal wintering areas are so far secure.

Population trend

declining