Steller's sea eagle

Steller's sea eagle (Haliaeetus pelagicus), also known as the Pacific sea eagle or white-shouldered eagle, is a very large diurnal bird of prey in the family Accipitridae. It was described first by Peter Simon Pallas in 1811. No subspecies are recognised. A sturdy eagle, it has dark brown plumage with white wings and tail, a yellow beak, and yellow talons. Typically, it is the heaviest eagle in the world, at about 5 to 10 kg (11 to 22 lb), but in some standard measurements, may be ranked below the harpy eagle (Harpia harpyja) and the Philippine eagle (Pithecophaga jefferyi). Steller's sea eagle females are bigger than males, similar to other raptors.

The Steller's sea eagle is endemic to coastal northeastern Asia, where it lives in Russia, Korea, Japan, and China. It mainly preys on fish and water birds. The Kamchatka Peninsula in Far Eastern Russia is known for its relatively large population of these birds; about 4,000 of these eagles live there. Steller's sea eagle is listed as vulnerable on the International Union for Conservation of Nature's Red List (IUCN Red List) of threatened species.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Steller's sea eagle is known to make a deep barking cry, ra-ra-ra-raurau. In aggressive interactions, its call is 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 other that sound like very loud, deep-voiced gulls.