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White-bellied sea eagle

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White-bellied Sea Eagle
In Gippsland, Victoria
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Aves
Order:
Falconiformes
(or Accipitriformes, q.v.)
Family:
Accipitridae
Genus:
Haliaeetus
Species:
H. leucogaster
Binomial name
Haliaeetus leucogaster
Gmelin, 1788
Range shown in green

The White-bellied Sea Eagle (Haliaeetus leucogaster), also known as the White-breasted Sea Eagle, is a large diurnal bird of prey in the family Accipitridae. It is closely related to Sanford's Sea Eagle of the Solomon Islands, the two considered a superspecies.

It is resident from India through southeast Asia to Australia on coasts and major waterways. It is a distinctive bird. The adult has 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 Haliaeetus species.[1]

Taxonomy

The White-bellied Sea Eagle was first described by the German naturalist Johann Friedrich Gmelin in 1788, although John Latham had earlier made notes on the species in 1781. Its specific name is derived from the Ancient Greek leuko- 'white',[2] and gaster 'belly'.[3] Its closest relative is the little-known Sanford's Sea-eagle of the Solomon Islands. These form a species pair, and as is usual in sea eagle species pairs, the White-bellied Sea-eagle has a white head, as opposed to the dark-headed Sanford's. The talons, bill, and eyes are dark as in all Gondwanan sea eagles. This species pair has at every age at least some dark colouration in its tail, though this may not always be clearly visible in White-bellied. The nucleotide sequences of the cytochrome b gene of the two sea eagles were among those analysed in a 1996 study. Although they differ much 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. Wink and colleagues 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.[4] Researchers Ingrid Seibold and Andreas J. Helbig, who analysed and compared the same nucleotide sequences along with morphology and allozyme data, proposed that the Sanford's Sea Eagle might have only recently colonised the Solomon Islands, having arisen from New Guinea-based White-bellied Sea Eagles.[5]

White-bellied's placement beyond its relationship with Sanford's Sea Eagle are a little less clear; molecular data indicate that it is one of four species of tropical sea eagles (the other two being the African Fish Eagle and the Madagascar Fish Eagle), while allozyme data indicate it might have a closer relationship with the northern hemisphere sea eagles.[5][6] 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 Ichthyophaga).[7]

As well as White-bellied Sea Eagle and White-breasted Sea Eagle, other recorded names include White-bellied Fish-hawk, White-eagle, and Sea-eagle.[8]

Description

In Gippsland, Victoria, Australia

The White-bellied Sea Eagle is one of the largest raptors in Southeast Asia, and the second largest bird of prey in Australia, after the Wedge-tailed Eagle (Aquila audax) which stands up to 1 m.

The head, rump and underparts are white, and the back and wings are dark grey. 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 eagles of the genus Aquila, the legs are not feathered. The sexes are similar. Males are 70–80 cm (28–32 in) and weigh 1.8–3 kg (4–6.6 lb). Females are slightly larger, at 80–90 cm (32–36 in) and 2.5–4.5 kg (5.5–10 lb). The wingspan ranges from 1.8 to 2.2 m (6–7 ft).[9] 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 (females larger than males), and that birds from latitudes further south were larger than those from the north.[10] There is no seasonal variation in plumage.[11] 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.[12]

They soar on thermals holding their wings in a 'V' shape, unlike most other raptors which hold them horizontally.[13] They modifiy their wings when gliding so that they arise from the body at an angle, but are more horizontal further out along the wingspan. In silhouette, the comparatively long neck, head and beak stick stick out from the front almost as far as the tail does behind. For active flight, the White-bellied Sea Eagle alternates strong deep wingbeats with short periods of gliding.[11]

Young sea-eagles in their first year are predominantly brown,[9] with pale cream streaked plumage on their head, neck, nape and rump areas.[11] Their plumage becomes more infiltrated with white until they acquire the complete adult plumage by their fourth or fifth year.[9] The loud goose-like honking call is a familiar sound, particularly during the breeding season; pairs often honk in unison,[14] and often carry on for some time when perched. The male's call was higher-pitched and more rapid than that of the female. Australian naturalist David Fleay observed that the call was among the loudest and furthest-carrying of all Australian bird calls, in stark contrast to the relatively quiet calls of the Wedge-tailed Eagle.[15]

Adult birds are unmistakable and unlikely to be confused with any other bird. Immatures 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 a more undulating flight.[16]

Distribution and habitat

The White-bellied Sea Eagle is found from Bangladesh, India and Sri Lanka in southern Asia, through all of coastal Southeast Asia including Burma, Thailand, Malaysia, Indonesia, Indochina, the Philippines and southern China including Hong Kong,[14] eastwards through New Guinea and the Bismarck Archipelago,[17] and Australia. In the north Solomons it is restricted to Nissan Island,[18] and replaced elsewhere by Sanford's Sea-eagle.[17] In Victoria, where it is otherwise scarce, it is locally more common at Corner Inlet and Gippsland Lakes.[19] Similarly in South Australia, it is most abundant along the north coast of Kangaroo Island.[20] The range extends to the islands of Bass Strait and Tasmania, and it is thought able to move between the islands and the mainland.[21] There is one unconfirmed record from Lord Howe Island and several from New Zealand.[22]

They are a common sight in coastal areas, but may also be seen well inland.[23][24] The White-bellied Sea Eagle is generally sedentary and territorial, although may travel long distances. They have been reported travelling upriver to hunt for flying foxes (Pteropus). Populations in inland Australia move around as inland bodies of water appear and then dry up. In one instance, a pair came to breed at Lake Albacutya in northwestern Victoria after being empty for 30 years.[25] The species is easily disturbed by humans, especially when nesting, and is found in greater numbers in areas.

Behaviour

Adult flying in Karwar, Karnataka, India
Juvenile flying over East Wallabi Island, an Australia island in the Indian Ocean

The White-bellied Sea Eagle is territorial, with some birds form permanent pairs that inhabit territories throughout the year, while others are nomadic. The species is monogamous, with pairs remaining together until one bird dies, after which the surviving bird quickly seeks a new mate. This can lead to some nest sites being continuously occupied for many years, one such site in Mallacoota for over fifty years.[26] Immature birds are generally dispersive, with many moving over 50 km (30 mi) away from the area they were raised. One juvenile raised in Cowell, South Australia was reported 3000 km (1800 mi) away at Fraser Island in Queensland.[27] Study of the species in Jervis Bay showed increases in the numbers of immature and subadult birds in autumn, although it was unclear whether these were locally-fledged birds or (more likely) an influx of young birds born and raised elsewhere in Australia.[28]

Birds are often seen perched high in a tree, or soaring over waterways and adjacent land. They are often encountered singly or in pairs. Small groups of White-bellied Sea Eagles are sometimes encountered, in which case all but two of the group are immature birds.[28]

Much of the White-bellied Sea Eagle's behaviour, particularly breeding, remain poorly known.[29]

Feeding

The White-bellied Sea Eagle is an opportunistic carnivore, and consumes a wide variety of animal prey, including carrion.[27] It often catches fish by flying low over the water and catching prey with its talons.[9] It prepares for the strike by holding its feet far forward almost under its chin and striking backwards and simultaneously beating its wings to lift upwards. Generally only one foot is used to seize prey.[27] The White-bellied Sea Eagle may also dive at a 45 degree angle from its perch and briefly submerge to a depth of 40 cm (16 in) to catch fish near the water surface.[citation needed] They keep within 1 km (0.6 mi) of shores, as there are no thermals over water.

The White-bellied Sea Eagle hunts mainly aquatic animals, such as fish, turtles and sea snakes,[30] but it takes birds, such as Little Penguins, coots and shearwaters, and mammals as well.[9] In the Bismarck Archipelago it has been reported feeding on various species of possum.[31] It is a skilled hunter, and will attack prey up to the size of a swan. They also feed on carrion such as dead sheep, birds and fish along the waterline, as well as raiding fishing nets and following cane harvesters. They harass smaller raptors such as Swamp Harriers, Whistling Kites, Brahminy Kites and Ospreys, forcing them to drop any food that they are carrying.[9][27] Other birds victimised include Silver and Pacific Gulls, cormorants and Australasian Gannets. They may even thieve off their own species, including their mate. The White-bellied Sea Eagle attacks these birds by striking them with outstretched talons from above, or by flying upside down underneath the smaller predator and snatching the prey, all the while screeching a shrill scream. Sea Eagles feed alone, in pairs or in family groups. A pair may cooperate to hunt prey.[27]

A 2006 study of inland bodies of water around Canberra where Wedge-tailed Eagles and White-bellied Sea Eagles share territories showed that there was little overlap in the range of prey taken. The former took rabbits, various macropods, and terrestrial birds such as cockatoos and parrots, and various passerines including magpies and starlings, while the latter 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 Australian Wood Duck. Rabbits constituted only a small fraction of the White-bellied Sea Eagle's diet. Depite nesting near each other, the two species seldom interacted, as the Wedge-tailed Eagles hunted away from water and the White-bellied foraged along the lake shores.[32]

Breeding

A dead branch makes a good perch to survey the surrounding area.

The breeding season varies according to location—it has been recorded in the dry season in the Trans-Fly region and Central Province of Papua New Guinea,[17] and from June to August in Australia.[33] They usually choose the tallest trees in which to nest, and sometimes man-made pylons. Often, locations are sought where there is a dead tree or branch at height with good visibility which can be used as a perch to survey the surrounding area.[16] 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 over time. Nests are generally sited in the forks of large trees overlooking bodies of water.[34] Cliffs are also suitable nesting sites, while nests built directly on the ground are found on islands. A breeding pair, with the male being more active, spends three to six weeks building or renovating the nest before laying eggs.[29] Normally a clutch of two dull, white, oval eggs are laid. Measuring 73 x 55 mm.[33] they are incubated over six weeks before hatching. The young are semi-altricial, and covered in white down when they emerge from the egg. The male brings food and the female feeds the chicks early on, but both parents feed the chicks as they grow larger. Although two eggs are laid, it is unusual for two young to be reared successfully to fledging (leaving the nest). One egg may be infertile, and the second chick sometimes dies in the nest.[35] Nestlings have been recorded fledging anywhere from 70 to 84 days old, and remaining around the parents' territory for a further five or six months or until the following breeding season.

Conflict with Wedge-tailed Eagles over nesting sites in remnant trees has been recorded in Tasmania.[28]

Conservation status

The White-bellied Sea Eagle is listed as being of Least Concern by the IUCN.[36] There are an estimated 10 to 100 thousand individuals, although there seems to be a decline in numbers.

A review of average egg-shell thickness between 1947 and 1993 to evaluate the impact of DDT on egg breakage found that the shells of White-bellied Sea Eagle eggs had thinned by 6%, not thought likely to result in more breakage overall although individual clutches would have been more affected. Despite this, the result, the species 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.[37]

Australia

The White-bellied Sea Eagle is listed as marine and migratory under Australia's federal Environment Protection and Biodiversity Conservation Act 1999. As a mainly coastal species, it is vulnerable to habitat destruction in Australia's increasingly populated and urbanised coastal areas, particularly in the south and east of the country, where it appears to have declined in numbers. However, there may have been an increase in population inland, secondary to the creation of reservoirs, dams and weirs, and the spread of the introduced Common carp (Cyprinus carpio). Furthermore, it is rare along the Murray River where it was once common.[38] It is also listed as threatened under Victoria's Flora and Fauna Guarantee Act (1988), with possibly under 100 breeding pairs remaining in the state.[19] Under this act, an action statement for the recovery and future management of this species has been prepared.[39] On the 2007 advisory list of threatened vertebrate fauna in Victoria, the White-bellied Sea-eagle is listed as vulnerable.[40]

There are fewer than 1000 adult birds in Tasmania, where the species is listed as vulnerable under Schedule 3.1 of the Tasmanian Threatened Species Protection Act 1995. It is threatened tehre by nest disturbance, loss of suitable nesting habitat, shooting, poisoning, trapping, and collision with power lines and wind turbines, as well as entanglement and environmental pollution. Estuaries are a favoured habitat, and often subject to environmental disturbance.[41]

Cultural significance

Known as Manulab to the people of Nissan Island, the White-bellied Sea Eagle is considered special and its killing is forbidden. Its calls at night are said to foretell danger, and seeing a group of eagles flying overhead calling is a sign that someone has died.[42] A local Sydney name was gulbi, and the bird was the totem of the late 18th century indigenous leader Colebee, of the Cadigal people.[43] 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 Jerrinja community know it as Manyanya, the word derived from the Dharawal language group, while the people of the Wreck Bay community call it Bugain (from the Dhurga language, which is part of the Yuin group).[8]

The White-bellied Sea Eagle is also important to the Mak Mak people of floodplains to the southwest of Darwin in the Northern Territory, who recognised its connection with "good country". It is their totem and integrally connected to their land.[44] The term Mak Mak is their name for the species (and themselves).[45] Marrawuddi is a name from Arnhem Land.[46] Known as nairanaa (among other names), it was similarly symbolic to the Tasmanian indigenous people.[47]

A Malay name is burung hamba siput "slave of the shellfish", Malay tales told of the sea-eagle screaming at the turning of tides to warn the shellfish.[48] The White-bellied Sea-eagle is also the emblem of the state of Selangor.[48] It is also featured on the $10,000 Singapore note.[48] It is the emblem of the Manly-Warringah Sea Eagles rugby league team.[8]

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 on film, however, their nest collapsed in February 2011.[49] The story attracted statewide attention.[50]

References

  1. ^ del Hoyo, J.; Elliott, A.; Sargatal, J., eds. (1994). Handbook of the Birds of the World. Vol. 2. Barcelona: Lynx Edicions. ISBN 84-87334-15-6.
  2. ^ Liddell & Scott 1980, p. 411.
  3. ^ Liddell & Scott 1980, p. 138.
  4. ^ Wink, Heidrich & Fentzloff 1996, pp. 783–91.
  5. ^ a b Seibold & Helbig 1996, pp. 103–12.
  6. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi: 10.1016/0305-1978(95)00001-B , please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi= 10.1016/0305-1978(95)00001-B instead.
  7. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi: 10.1016/j.ympev.2005.04.010 , please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi= 10.1016/j.ympev.2005.04.010 instead.
  8. ^ a b c Baldwin, Amanda (2010). "The White-bellied sea-eagle in the Jervis Bay region: an exploration of the cultural, ecological and conservation significance". Master of Science thesis, University of Wollongong. School of Earth & Environmental Sciences, University of Wollongong. Retrieved 2 May 2011.
  9. ^ a b c d e f Hollands 2003, p. 196.
  10. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi: 10.1071/MU03043 , please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi= 10.1071/MU03043 instead.
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  12. ^ Marchant & Higgins 1993, p. 92.
  13. ^ Tan, Ria (2001). "White-bellied fish eagle (Haliaeetus leucogaster): info fact sheet, photos". Naturia.per.sg. Retrieved 22 March 2010.
  14. ^ a b Strange 2000, p. 73.
  15. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi: 10.1071/MU948020 , please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi= 10.1071/MU948020 instead.
  16. ^ a b Marchant & Higgins 1993, p. 83.
  17. ^ a b c Coates 1985, pp. 116–17.
  18. ^ Hadden 2004, p. 63.
  19. ^ a b "Flora and Fauna Guarantee Action Statement: White-bellied Sea Eagle (Haliaeetus leucogaster)" (PDF). Department of Sustainability and Environment. Melbourne, Victoria: Department of Sustainability and Environment, State Government of Victoria. 2003. Retrieved 19 May 2011.
  20. ^ Dennis, Terry E.; Kinloch, Martine A.; Pisanu, Phil; King, Cameron (2005). "The distribution and breeding status of White-bellied Sea-Eagle and Osprey populations on Kangaroo Island in 2005". Kingscote, Kangaroo Island: Kangaroo Island Resources Board, Government of South Australia. Retrieved 18 May 2011.
  21. ^ Threatened Species Section, DPIW 2006, p. 13.
  22. ^ Marchant & Higgins 1993, p. 84.
  23. ^ Sadvi, K. M. (2009). "Occurrence of the White-bellied Sea Eagle Haliaeetus leucogaster in inland waters". Indian Birds. 5 (2): 50. ISSN 0973-1407.
  24. ^ Sriram, Mythili; Sriram, Tara; Anand, M. O. (2008). "Sighting of the White-bellied Sea Eagle Haliaeetus leucogaster at the Lakkavalli Dam". Indian Birds. 4 (2): 71. ISSN 0973-1407.
  25. ^ Tarr, H.E. (1962). "Observations on the White-breasted Sea-Eagle". Australian Bird Watcher. 1: 194–97.
  26. ^ Marchant & Higgins 1993, p. 87.
  27. ^ a b c d e Marchant & Higgins 1993, p. 85.
  28. ^ a b c Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi: 10.1071/MU04030 , please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi= 10.1071/MU04030 instead.
  29. ^ a b Debus 2008, pp. 165–93.
  30. ^ Gopi, G. V.; Pandav, Bivash (2006). "White-bellied Sea-Eagle Haliaeetus leucogaster preying on salt-water crocodile Crocodylus porosus" (PDF). Indian Birds. 2 (6): 171. ISSN 0973-1407.
  31. ^ Heinsohn 2000, pp. 245–46.
  32. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi: 10.1071/MU05046 , please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi= 10.1071/MU05046 instead.
  33. ^ a b Beruldsen 2003, p. 200.
  34. ^ Marchant & Higgins 1993, p. 89.
  35. ^ Marchant & Higgins 1993, p. 90.
  36. ^ "Haliaeetus leucogaster". iucnredlist.org. 2011 [last update]. Retrieved 2011-05-08. {{cite web}}: Check date values in: |year= (help)CS1 maint: year (link)
  37. ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi: 10.1071/MU9930001 , please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi= 10.1071/MU9930001 instead.
  38. ^ Department of Sustainability, Environment, Water, Population and Communities (2011). "Haliaeetus leucogaster — White-bellied Sea-Eagle". Threats Database, Department of Sustainability, Environment, Water, Population and Communities. Canberra, ACT: Australian Government. Retrieved 19 May 2011.{{cite web}}: CS1 maint: multiple names: authors list (link)
  39. ^ Department of Sustainability and Environment, Victoria[dead link]
  40. ^ Victorian Department of Sustainability and Environment (2007). Advisory List of Threatened Vertebrate Fauna in Victoria – 2007. East Melbourne, Victoria: Department of Sustainability and Environment. p. 15. ISBN 978-1-74208-039-0.
  41. ^ Threatened Species Section, DPIW 2006, p. 14.
  42. ^ Hadden 2004, p. 265.
  43. ^ Smith, Keith Vincent (2005 July). "Port Jackson People". NLA News. XV (10). National Library of Australia. ISSN 1444-1845. Retrieved 2011-05-08. {{cite journal}}: Check date values in: |date= (help)
  44. ^ Rose, Deborah Bird (1996), Nourishing Terrains: Australian Aboriginal Views of Landscape and Wilderness (PDF), Canberra, ACT: Australian Heritage Commission, p. 29, ISBN 9780642235619, OCLC 221843038, retrieved 24 May 2011
  45. ^ Daiyi, Linda Ford; Rose, Nancy Deborah (2002). "Life in Country:Ecological Restoration on Aboriginal Homelands". Cultural Survival.org website. Cambridge, MA: Cultural Survival.org. Retrieved 24 May 2011.
  46. ^ The Aboriginal Traditional Owners of Kakadu National Park and the Commonwealth of Australia. "Bardedjilidji" (PDF). Environment Australia website (Kakadu National Park). Australian Government. Retrieved 24 May 2011.
  47. ^ Threatened Species Section, DPIW 2006, p. 9.
  48. ^ a b c Pwee, Timothy (2002). "White-bellied sea eagle". Singapore Infopedia. National Library Board Singapore. Retrieved 31 July 2009.
  49. ^ "EagleCam". Birds Australia website. Birds Australia. 8 February 2011. Retrieved 5 April 2011.
  50. ^ Huxley, John (18 October 2010). "When baby eagles dare, we will be watching". Sydney Morning Herald. Fairfax Publications. Retrieved 5 April 2011.

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