White-bellied sea eagle

The white-bellied sea eagle (Icthyophaga leucogaster), also known as the white-breasted sea eagle, is a large diurnal bird of prey in the family Accipitridae. Originally described by Johann Friedrich Gmelin in 1788, it is closely related to Sanford's sea eagle of the Solomon Islands, and the two are considered a superspecies. A distinctive bird, the adult white-bellied sea eagle has a white head, breast, under-wing coverts and tail. The upper parts are grey and the black under-wing flight feathers contrast with the white coverts. The tail is short and wedge-shaped as in all Haliaeetinae species. Like many raptors, the female is larger than the male, and can measure up to long with a wingspan of up to , and weigh . Immature birds have brown plumage, which is gradually replaced by white until the age of five or six years. The call is a loud goose-like honking.

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.

Taxonomy

The white-bellied sea eagle was formally described by the German naturalist Johann Friedrich Gmelin in 1788 under the binomial name Falco leucogaster. Gmelin based his account on the "white-bellied eagle" that had been described in 1781 by John Latham from a specimen in the Leverian collection that had been obtained in February 1780 at Princes Island off the westernmost cape of Java during Captain Cook's last voyage. It is now one of six eagles placed in the genus Icthyophaga that was introduced in 1843 by the French naturalist Marie Jules César Savigny. Its specific name is derived from the Ancient Greek leuko- 'white', and gaster 'belly'. Its closest relative is the little-known Sanford's sea eagle of the Solomon Islands. These form a superspecies, and as is usual in other sea eagle superspecies, one (the white-bellied sea eagle) has a white head, as opposed to the other species' dark head. The bill and eyes are dark, and the talons are dark yellow as in all Southern Hemisphere sea eagles. Both these species have at least some dark colouration in their tails, though this may not always be clearly visible in the white-bellied sea eagle. The nucleotide sequences of the cytochrome b gene of the two sea eagles were among those analysed in a 1996 study. Although they differ greatly in appearance and ecology, their genetic divergence of 0.3% indicates that the ancestors of the two forms might have diverged as recently as 150,000 years ago. The study authors conclude that although the genetic divergence is more consistent with subspecies, the distinctness in appearance and behaviour warrants the two being retained as separate species. Mitochondrial sequence of the cytochrome b locus differs very slightly from that of Sanford's sea eagle suggesting a relatively recent divergence after New Guinea-based white-bellied sea eagles colonised the Solomon Islands.

The white-bellied sea eagle's affinities beyond the Sanford's sea eagle are a little less clear; molecular data indicate that it is one of four species of tropical sea eagle (along with the African fish eagle and the Madagascar fish eagle), while allozyme data indicate it might have a closer relationship with the sea eagles of the northern hemisphere. A further molecular study published in 2005 showed the white-bellied and Sanford's sea eagles to be basal to the four fish eagles (the two mentioned above plus the two hitherto untested species of the genus Icthyophaga).

As well as white-bellied sea eagle and white-breasted sea eagle, other recorded names include white-bellied fish-hawk, white-eagle, 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. and in the past in the Lakshadweep Islands) eastwards in India, Bangladesh, and Sri Lanka in southern Asia, through all of coastal Southeast Asia including Burma, Thailand, Malaysia, Indonesia, Indochina, the main and offshore islands of the Philippines, and southern China including Hong Kong, Hainan and Fuzhou, eastwards through New Guinea and the Bismarck Archipelago, and Australia. In the northern Solomons it is restricted to Nissan Island, and replaced elsewhere by Sanford's sea eagle. In Victoria, where it is otherwise scarce, it is locally more common at Corner Inlet and Gippsland Lakes. A pair of white-bellied sea eagles performs skillful displays of flying before copulation: diving, gliding, and chasing each other while calling loudly. They may mirror each other, flying apart and copying each other swooping and swerving. A talon-grappling display has been recorded where the pair will fly high before one flips upside down and tries to grapple the other's talons with its own. If successful, the two then plunge cartwheeling before separating as they approach the ground. This behaviour has also been recorded as an aggressive display against a wedge-tailed eagle.

The white-bellied sea eagle usually chooses tall trees or man-made pylons to nest in. Often, locations are sought where there is a tall dead tree or high branch with good visibility which can be used as a perch to survey the surrounding area, which is generally a low-lying locale near water with some forest cover. The perch becomes covered in faeces and pellets and animal remains litter the immediate surrounding area. The nest is a large deep bowl constructed of sticks and branches, and lined with such materials as grass or seaweed. Yearly renovations result in nests getting gradually bigger. Nests are generally sited in the forks of large trees overlooking bodies of water. Old nests of wedge-tailed eagles or whistling kites have been renovated and used. Other important fish prey includes needlefish and wrasses. Along with osprey, white-bellied sea-eagles sometimes take fish that are toxic, including some porcupinefish and Tetraodontidae fish. In one case, the fish eagle attempted to prey on an adult Asian water monitor (Varanus salvator). The eagle attacked the 1.5m long lizard and delivered a fatal injury, though it couldn't carry it due to the lizard's weight.

They frequently take waterfowl and seabirds, such as little penguins, Eurasian coots, and shearwaters. It is a skilled hunter and will attack seabirds up to the size of a gull, cormorant, gannet, and waterfowl up to the size of magpie goose (Anseranas semipalmata). In the Bismarck Archipelago, it has been reported feeding on domestic dogs, cats, and two species of possum, the northern common cuscus and common spotted cuscus.

White-bellied sea eagles feed alone, in pairs, or in family groups. A pair may cooperate to hunt. Prey can be eaten while the bird is flying or when it lands on a raised platform such as its nest. The white-bellied sea eagle skins the victim as it eats it. It is exceptionally efficient at digesting its food and disgorges only tiny pellets of fragmented bone, fur, and feathers.

A 2006 study of inland bodies of water around Canberra where wedge-tailed eagles and white-bellied sea eagles share territories showed little overlap in the range of prey taken. Wedge-tailed eagles took rabbits, various macropods, terrestrial birds such as cockatoos and parrots, and various passerines including magpies and starlings. White-bellied sea eagles caught fish, water-dwelling reptiles such as the eastern long-necked turtle and Australian water dragon, and waterbirds such as ducks, grebes and coots. Both species preyed on the maned duck. Rabbits constituted only a small fraction of the white-bellied sea eagle's diet. Despite nesting near each other, the two species seldom interacted, as the wedge-tailed eagles hunted away from water and the white-bellied sea eagles foraged along the lake shores. In the Eyre Peninsula in South Australia, nests have been vacated as human activities have encroached on the eagles' territories. Elsewhere, the clearing of trees suitable for nesting has seen it largely disappear locally, such as the removal of stands of Casuarina equisetifolia in Visakhapatnam district in Andhra Pradesh in India. In India, nest densities of about one per 4.32 km of coastline have been noted in Sindhudurg and one per 3.57 km (45 nests along 161 km) in Ratnagiri district of Maharashtra. They also nest on Netrani Island, where about a 100 birds were noted in 1875 (then known as Pigeon Island) by Allan Octavian Hume who noted that this was perhaps the largest breeding colony of the species. In 2000, the disturbance to the island from torpedo-firing exercises conducted by the Indian navy was noted as a threat. Nearly 100 nests have been noted in 2004 on this island.

DDT was a widely used pesticide in agriculture that was found to have significant adverse effects on wildlife, particularly egg thinning and subsequent breakage in birds of prey. A review of DDT's impact on Australian raptors between 1947 and 1993 found that the average egg-shell thickness had decreased by 6%. This average level of thinning was not thought likely to result in significantly more breakage overall, however individual clutches that had been even thinner might have broken. The white-bellied sea eagle was one of the more affected species, probably due to its feeding in areas heavily treated with pesticide such as swamps. DDT use peaked in 1973, but was no longer approved after 1987 and its use had effectively ceased by 1989.

Cultural significance

thumb|Adult flying in Tasmania

The white-bellied sea eagle was important to different tribes of indigenous people across Australia. The guardian animal of the Wreck Bay aboriginal community, it is also the official emblem of the Booderee National Park and Botanic Gardens in the Jervis Bay Territory. The community considered localities around Booderee National Park to be connected with it.

The white-bellied sea eagle is featured on the $10,000 Singapore note, It is the emblem of the Malaysian state of Selangor. The bird is the emblem of the Manly-Warringah Sea Eagles rugby league team, From 2010, a nesting pair of white-bellied sea eagles have had their attempts at raising chicks filmed live on "EagleCam", with footage on display at the nearby Birds Australia Discovery Centre in Sydney Olympic Park, New South Wales. After raising one brood, however, their nest collapsed in February 2011.

References

General references

External links

White-bellied Sea Eagle at Animal Diversity Web, University of Michigan