Wedge-tailed Eagle (Aquila Audax)
Spiralling gracefully upwards on a thermal updraft, a pair of magnificent wedge-tailed eagles corkscrews around each other in one of the most awesome displays in the Australian bush.
Imagine a bird with wingspan of over 2.3 metres—they are the largest bird of prey in Australia, and one of the largest eagles in the world!
‘Wedgies’ at Billabong Sanctuary had originally been housed in the ‘Blechdome’, a huge aviary designed and built for us in 2000 by two Dutch students, Jeroen Nyssen and Roel de Waal, working here while they studied animal management.
Unfortunately it got smashed by Cyclone Yasi, and the eagles were relocated. We are happy to report that we have now rebuilt the aviary, and a splendid young female eagle named Aurora is now in residence.
Thunder, a young male wedgie, is currently in training behind the scenes, but will soon join the afternoon free-Flight Bird Show.
What’s in a Name?
The genus name Aquila comes from the Latin word for eagle. The species name audax means ‘bold’ in Latin. Thus the wedge-tailed eagle’s scientific name translates to ‘Bold Eagle’.
What do they Look Like?
In comparison to other birds of prey, its size and shape make the wedge-tailed eagle unmistakeable. The wingspan can reach more than 2.3 metres (about 7 1/2 feet)!
Females are slightly larger than males, and can reach 105 cm in length (over 40 in) and weigh up to 4 kg (nearly 9 lb)!
Adult wedge-tailed eagles are mostly very dark brownish-black, with paler brown feathers on the nape of the neck and on the wing coverts.
The tail is long and flares outwards before tapering to a wedge-shaped point, and the long legs are feathered down to the base of the toes.
Young birds are mid-brown in colour, and darken progressively after about 5 or 6 years of age. Adult males and females have similar plumage. The beak is pale pink to cream-coloured, and the feet are off-white.
This bird is more likely to be seen in flight, soaring high on air currents. There you can recognize its distinctive silhouette, with upcurved wingtips, flight feathers stretched out like fingers, and that long wedge-shaped tail.
Where do they Live?
The wedge-tailed eagle is found all over mainland Australia, as well as on Tasmania and in southern Papua New Guinea.
The Tasmanian eagle is a sub-species, Aquila audax fleayi. It has lighter feathers on the nape of the neck, and longer talons than the mainland race (A audax audax).
Wedge-tailed eagles live in a variety of habitats, from the sea coast to high alpine regions in the mountains. In general, they prefer open or wooded country, and avoid rainforest and coastal heaths.
They are often seen soaring high on thermals, at altitudes up to 2000 metres (6500 ft—well over a mile)!
What do they Eat?
You would expect such a huge, powerful bird to be a ferocious hunter. Although not as swift as other birds of prey such as falcons and sparrow hawks the wedge-tailed eagle is a powerful hunter.It will swoop down onto a fleeing rabbit or wallaby and strike it with the enormous rear talon, killing it instantly.
From its vantage point soaring high above open ground, it is also quick to spot freshly-killed animals, and carrion makes up a large part of its diet. Its large hooked beak is strong enough to rip open thick hides and break bones.
Wedge-tailed eagles eat a wide variety of mammals, lizards and birds, depending on their local abundance.
Mammals make up the greatest share of their diet, and rabbits are the most important live prey taken. They will also eat possums, gliders, cats, dogs, piglets, kangaroos, wallabies, lambs, goats, calves and foxes.
Most of these animals are introduced species, brought to Australia by European settlers. That they make up such a large part of the eagle’s diet is an indication of its adaptability.
Reptiles over 40 gm in weight (over an ounce and a half) such as thorny devils, blue-tongue skinks and goannas are eaten.
Ground-foraging birds such as parrots, doves, and baby emus and bustards are also taken.
Wedge-tailed eagles will sometimes pack together to hunt down a large animal such as a wallaby. It is this behaviour that earned them their Latin name, which means ‘Bold Eagle’.
A Wedge-tailed eagle is capable of lifting and flying off with an animal up to 5 kg in weight (over 10 pounds) which is heavier than its own body weight!
Breeding and Nesting
Wedge-tailed eagles mate for life. A pair will establish a breeding territory, and defend it from other eagles, as well as other intruders- there are reports that they even attack helicopters or hang gliders! Beyond this area is their home range, where they hunt for food. The size of this area depends on the abundance of food species. The eagles do not actively defend this larger area, but advertise their presence by gliding high overhead, soaring for up to 90 minutes at a time.
The breeding season is heralded by amazing acrobatic displays in flight. The male dives down towards the female, pulling out before he reaches her and zooming back upwards with partially folded wings. She may turn on her back (in mid-air) and present her claws to him, and they spiral upwards together, screeching and calling. They will also perch next to each other and preen one another as mating season approaches.
Within their territory, a pair may build several nests, which they use in rotation over the years. Usually these are built in the tallest trees within their territory. If trees are scarce they may also nest on cliffs.
The nest is a huge bowl of dead sticks and small branches, built into the fork of the tree. The tree has to be very strong, because the nest may weigh up to 400 kg (880 pounds)! As the nest is re-used and added to in successive years, it can reach over 2 metres in diameter (over 6 ft) and be 3 metres deep (nearly 10 feet!). The nest is lined with green leaves; both male and female eagles regularly add fresh leaves throughout the breeding season.
Eggs are laid from June to about August in the south and from April to September in the north. The female lays from 1 to 3 eggs, but usually 2. They are white to pale buff-grey, splotched with purple and brown, rounded to oval in shape, and about 75 x 60 mm (3 x 2.3 inches)—the size of a goose egg.
Raising the Young
Both male and female incubate the eggs, which hatch after about 43 days. The chicks are covered in fine white down. Both parents collect food, but the male usually does most of the hunting. Prey animals are shredded and bits of meat poked into the chick’s mouth for the first 5 weeks or so. After this time the chicks can pick up food for themselves from the floor of the nest. Carrion is not fed to chicks.
After about 70 to 88 days the chicks have grown their juvenile feathers. They remain with their parents for about 3 months after leaving the nest. After this time they will disperse to find a new home range. Some juveniles have been known to move over 800 km from their nest site (over 500 miles)!
Wedge-tailed eagles do not reach sexual maturity until they are 5 or 6 years of age. They may live for up to 40 years!
Status in the Wild
Early in the 20th century, it was thought that wedge-tailed eagles were killing large numbers of sheep and lambs. Bounty money was offered for their destruction, and huge numbers were poisoned or shot right up till the 1970’s. In one year in Queensland alone over 10 000 bounties were paid.
It was later realized that eagles were mostly feeding on carrion, or taking only lambs in poor condition, and in fact were not harming the sheep industry at all. Now they are protected in all states by the National Parks and Wildlife Act.
In some ways wedge-tailed eagles have benefited from European settlement. Rabbits were introduced, and became an important food source, along with other domestic animals and livestock. To some extent, clearing of forests has opened up new hunting areas. Eagles have learned to exploit the carcasses of road-killed animals that litter Outback highways.
But continued tree-clearing will lead to loss of nesting sites, especially in arid areas. If people disturb a nest, the eagles may abandon it for that year.
Indirect poisoning from dingo baits and pesticides is an on-going problem. Eagles themselves have become the victims of highway traffic, as large numbers are now being killed as they feed on dead animals by the road.
Nevertheless, at this time wedge-tailed eagles in mainland Australia are not considered to be threatened.
Generations to come will continue to be moved by the stirring sight of these huge, majestic birds soaring high above the landscape.
It is a different story in Tasmania, where the subspecies is considered to be critically endangered. There are less than 1000 birds remaining. Biologists have identified about 220 nesting territories, where it is estimated as few as 80 pairs of eagles are successfully breeding each year.
There has been a dramatic loss of habitat because of clearing of old-growth eucalyptus forests. Most nests are now found on private land or in State forests, and are therefore subject to frequent disturbance. Wedge-tailed eagles will abandon a nest if disturbed during the breeding season. Stock owners continue to illegally kill eagles by shooting, trapping and poisoning.
A Recovery Plan has been put into place by the Tasmanian government. There are two main objectives: to identify nesting sites so that they can be protected from further forest clearing, and to educate landowners and enlist their support in conservation of wedge-tailed eagles.
If the plan does not succeed, the Tasmanian wedge-tailed eagle may not survive in the wild. What a sad loss that would be.