White-bellied sea eagle

Resident from India and Sri Lanka through Southeast Asia to Australia on coasts and major waterways, the white-bellied sea eagle breeds and hunts near water, and fish form around half of its diet. Opportunistic, it consumes carrion and a wide variety of animals. Although rated as Least Concern globally, it has declined in parts of southeast Asia such as Thailand, and southeastern Australia. It is ranked as Threatened in Victoria and Vulnerable in South Australia and Tasmania. Human disturbance to its habitat is the main threat, both from direct human activity near nests which impacts on breeding success, and from removal of suitable trees for nesting. The white-bellied sea eagle is revered by indigenous people in many parts of Australia, and is the subject of various folk tales throughout its range.

The white-bellied sea eagle has a white head, rump and underparts, and dark or slate-grey back and wings. In flight, the black flight feathers on the wings are easily seen when the bird is viewed from below. The large, hooked bill is a leaden blue-grey with a darker tip, and the irides are dark brown. The cere is also lead grey. The legs and feet are yellow or grey, with long black talons (claws). Unlike those of eagles of the genus Aquila, the legs are not feathered. The sexes are similar. Males are 66–80 cm (26–31 in) long and weigh 1.8–3 kg (4.0–6.6 lb). Females are slightly larger, at 80–90 cm (31–35 in) and 2.5–4.5 kg (5.5–9.9 lb). The wingspan ranges from 1.78 to 2.2 m (5.8 to 7.2 ft). A 2004 study on 37 birds from Australia and Papua New Guinea (3 °S to 50 °S) found that birds could be sexed reliably on size, and that birds from latitudes further south were larger than those from the north. There is no seasonal variation in plumage. The moulting pattern of the white-bellied sea eagle is poorly known. It appears to take longer than a year to complete, and can be interrupted and later resumed from the point of interruption.

The wings are modified when gliding so that they rise from the body at an angle, but are closer to horizontal further along the wingspan. In silhouette, the comparatively long neck, head and beak stick out from the front almost as far as the tail does behind. For active flight, the white-bellied sea eagle alternates strong deep wing-beats with short periods of gliding.

A young white-bellied sea eagle in its first year is predominantly brown, with pale cream-streaked plumage on their head, neck, nape and rump areas. The plumage becomes more infiltrated with white until it acquires the complete adult plumage by the fourth or fifth year. The species breeds from around six years of age onwards. The lifespan is thought to be around 30 years.

The loud goose-like honking call is a familiar sound, particularly during the breeding season; pairs often honk in unison, and often carry on for some time when perched. The male's call is higher-pitched and more rapid than that of the female. Australian naturalist David Fleay observed that the call is among the loudest and furthest-carrying of all Australian bird calls, in stark contrast to the relatively quiet calls of the wedge-tailed eagle.

Adult white-bellied sea eagles are unmistakable and unlikely to be confused with any other bird. Immature birds can be confused with wedge-tailed eagles. However, the plumage of the latter is darker, the tail longer, and the legs feathered. They might also be confused with the black-breasted buzzard (Hamirostra melanosternon), but this species is much smaller, has white patches on the wings, and has a more undulating flight. In India, the Egyptian vulture has white plumage, but is smaller and has a whiter back and wings. The white tail of the white-bellied sea eagle in flight distinguishes it from other species of large eagles. In the Philippines, it can be confused with the Philippine eagle, which can be distinguished by its crest; immature white-bellied sea eagles resemble immature grey-headed fish eagles, but can be identified by their more wholly dark brown underparts and flight feathers, and wedge-shaped tail.