Wedge-tailed eagle

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Wedge-tailed eagle
Aquila audax - Captain's Flat.jpg
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Falconiformes
(or Accipitriformes, q.v.)
Family: Accipitridae
Genus: Aquila
Species: A. audax
Binomial name
Aquila audax
(Latham, 1802)

The wedge-tailed eagle (Aquila audax), sometimes known as the eaglehawk (both misnomers, as it is not a hawk, and its tail is shaped more like a diamond), is the largest bird of prey in Australia, and is also found in southern New Guinea. It has long, fairly broad wings, fully feathered legs and an unmistakable diamond-shaped tail. Because of both its tail and its size—it is one of the largest birds of prey in the world—it can be identified at a glance as a "Wedgie" even by the non-expert.

The wedge-tailed eagle is one of twelve species of large predominantly dark-coloured booted eagles in the genus Aquila found worldwide. A large brown bird of prey, it has a wingspan of up to 2.27 m (7 ft 5 in) and a length up to 1.06 m (3 ft 6 in).[2]

Description[edit]

In flight the diamond-shaped tail is clearly visible
Taking-off from its perch, the long legs of this adult female are clearly visible
Nest site in the Barmah-Millewa Forest
At Symbio Wildlife Park, New South Wales, Australia
Wedge-tailed eagle

The female wedge-tailed eagle weighs between 3 and 5.77 kg (6.6 and 12.7 lb), while the smaller males weigh 2 to 4 kg (4.4 to 8.8 lb).[2][3] Length varies between 81 and 106 cm (32 and 42 in) and the wingspan typically is between 182 and 232 cm (6 ft 0 in and 7 ft 7 in).[2][3] In 1930, the average weight and wingspans of 43 birds was 3.4 kg (7.5 lb) and 204.3 cm (6 ft 8 in).[4] The same average figures for a survey of 126 eagles in 1932 were 3.63 kg (8.0 lb) and 226 cm (7 ft 5 in), respectively.[5] The largest wingspan ever verified for an eagle was for this species. A female killed in Tasmania in 1931 had a wingspan of 284 cm (9 ft 4 in), another female measured barely smaller at 279 cm (9 ft 2 in).[5] Reported claims of eagles spanning 312 cm (10 ft 3 in) and 340 cm (11 ft 2 in) were deemed to be unreliable.[5] This eagle's great length and wingspan place it among the largest eagles in the world but its wings, at more than 65 cm (26 in), and tail, at 45 cm (18 in), are both unusually elongated for its body weight and 8-9 other eagle species regularly outweigh it.[3]

Young eagles are a mid-brown colour with slightly lighter and reddish-brown wings and head. As they grow older, their colour becomes darker, reaching a dark blackish-brown shade after about ten years (birds in Tasmania are usually darker than those on the mainland). Adult females tend to be slightly paler than males. Although it rarely needs to be distinguished from other Aquila eagles, its long, wedge-shaped tail is unique to this species.

Its range and habitat sometimes overlap with the white-bellied sea eagle, which is similar in size and shape and also has a somewhat diamond-shaped tail, although rather smaller and less distinctive. In silhouette and poor light, the two can look somewhat similar. Closer examination reveals the belly colour or tail size to distinguish the two.

Breeding and habitat[edit]

Aquila audax Egg - MHNT

Wedge-tails are found throughout Australia, including Tasmania, and southern New Guinea in almost all habitats, though they tend to be more common in lightly timbered and open country in southern and eastern Australia.

As the breeding season approaches, a pair of wedge-tailed eagles will perch close to each other and preen one other. They also perform dramatic aerobatic display flights together over their territory. Sometimes the male dives down at breakneck speed towards his partner. As he pulls out of his dive and rises just above her on outstretched wings, she either ignores him or turns over to fly upside down, stretching out her talons. The pair may then perform a loop-the-loop. The wedge-tailed eagle usually nests in the fork of a tree between one and thirty metres above the ground, but if there are no suitable sites, it will nest on a cliff edge.

Before egg laying, both birds will either destroy the large stick nest or add new sticks and leaf lining to an old nest. Nests can be 2–5 metres deep and 2–5 metres wide. The female usually lays two eggs, which are incubated by both sexes. After about 45 days, the chicks hatch. At first, the male does all the hunting. When the chicks are about 30 days old, the female stops brooding them and joins her mate to hunt for food.

The young wedge-tailed eagles depend on their parents for food for up to six months after hatching. They leave only when the next breeding season approaches.

Behaviour and diet[edit]

They are highly aerial, soaring for hours on end without wingbeat or effort, regularly reaching 1,800 metres (5,900 ft) and sometimes considerably higher. The purpose of this very high flight is unknown. Their keen eyesight extends into the infrared and ultraviolet bands. This helps them spot prey and allows them to see rising thermals, which they can use to gain altitude while expending little energy.

Feeding on carrion in the Pilbara region of Western Australia

Most prey is captured on the ground in gliding attacks or (less frequently) in the air. Choice of prey is very much a matter of convenience and opportunity: since the arrival of Europeans, the introduced rabbit and brown hare have become the primary items of the eagle's diet in many areas.[6] Larger introduced mammals such as foxes and feral cats are also occasionally taken, while native animals such as wallabies, small kangaroos, possums, koalas and bandicoots are also preyed on. In some areas, birds such as cockatoos, ducks, crows, ibis and even emu are more frequent prey items. Reptiles are less frequently taken, however frill-necked lizards, goannas and brown snakes are occasionally preyed on.

They display considerable adaptability, and have sometimes been known to team up to hunt large red kangaroos, to cause goats to fall off steep hillsides and injure themselves, or to drive flocks of sheep or kangaroos to isolate a weaker animal.[7]

Carrion is a major diet item also: wedge-tails can spot the activity of Australian ravens (sometimes known as crows) around a carcass from a great distance, and glide down to appropriate it. Wedge-tailed eagles are often seen by the roadside in rural Australia, feeding on animals that have been killed in collisions with vehicles.

This impressive bird of prey spends much of the day perching in trees or on rocks or similar exposed lookout sites such as cliffs from which it has a good view of its surroundings. Now and then, it takes off from its perch to fly low over its territory. During the intense heat of the middle part of the day, it often soars high in the air, circling up on the thermal currents that rise from the baking ground below. Each pair occupies a home range, which may extend from as little as 9 km2 (3.5 sq mi) to more than 100 km2 (39 sq mi). Within this home range lies a breeding territory around the nest. The eagle patrols the boundary of this home range and advertises its ownership with high-altitude soaring and gliding flights. It may defend its territory by diving on intruders. Adults are avian apex predators and have no natural predators but must defend their eggs and nestlings against nest predators such as corvids, currawongs, or other wedge-tailed eagles and in Tasmania there is often conflict with the white-bellied sea eagle over nest sites.

The wedge-tailed eagle is the only bird that has a reputation for attacking hang gliders and paragliders (presumably defending its territory). There are recorded cases of the birds damaging the fabric of these gliders with their talons.

The presence of a wedge-tailed eagle often causes panic among smaller birds and as a result, aggressive species such as magpies, butcherbirds, masked lapwings, and noisy miners aggressively mob eagles (see video).

Conservation status[edit]

The subspecies from Tasmania (Aquila audax fleayi) is listed as endangered by the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act)[8] with fewer than 200 pairs left in the wild. Like the Thylacine, the eagle was once subject to a bounty in Tasmania, as it was believed to prey on livestock.

Decreasing numbers of Tasmanian devils may be beneficial to the wedge-tailed eagles in Tasmania, as it could reduce competition for roadkill and devil predation on wedge-tailed eagle young.[9]

As an emblem[edit]

Parks and Wildlife Service Northern Territory (Australia) use the wedge-tailed eagle, superimposed over a map of the Northern Territory, as their emblem. The New South Wales Police Force emblem contains a wedge-tailed eagle in flight, as does the Northern Territory Correctional Services. La Trobe University in Melbourne also uses the wedge-tailed eagle in its corporate logo and coat of arms.[10] The Royal Australian Air Force and Australian Air Force Cadets Use the Wedge-Tailed on their badge.[11]

The West Coast eagles AFL football club uses a wedge-tailed eagle as their club mascot.

References[edit]

  1. ^ BirdLife International (2012). "Aquila audax". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013. 
  2. ^ a b c Debus, S.J.S. (1994). Wedge-tailed Eagle (Aquila audax). Pp. 198 in: del Hoyo, Elliott & Sargatal. eds. (1994). Handbook of the Birds of the World, vol. 2. ISBN 84-87334-15-6
  3. ^ a b c "Raptors of the World" by Ferguson-Lees, Christie, Franklin, Mead & Burton. Houghton Mifflin (2001), ISBN 0-618-12762-3
  4. ^ [1]
  5. ^ a b c Wood, Gerald (1983). The Guinness Book of Animal Facts and Feats. ISBN 978-0-85112-235-9. 
  6. ^ Brooker, M.G.; Ridpath, M.G. (1980). "The Diet of the Wedge-tailed Eagle, Aquila Audax, in Western Australia". Australian Wildlife Research 7 (3): 433–452. doi:10.1071/WR9800433. 
  7. ^ Beattie), William A. (1990). Beef Cattle Breeding & Management. Popular Books. ISBN 0-7301-0040-5. 
  8. ^ "Aquila audax fleayi — Wedge-tailed Eagle (Tasmanian)". Australian Government. Retrieved 25 January 2009. 
  9. ^ http://www.environment.gov.au/biodiversity/threatened/publications/recovery/pubs/draft-for-comment-tasmanian-devil.pdf
  10. ^ http://www.latrobe.edu.au/about/history/logo
  11. ^ http://www.airforce.gov.au