Aquila audax
wedge-tailed eagle

Wedge-tailed eagles or eaglehawks (Aquila audax) are found in the Australian region, spanning from the southern area of New Guinea through all of continental Australia and Tasmania. New Guinea and Australia are inhabited by the subspecies A. a. audax, while Tasmania is home to the subspecies A. a. fleayi. (Blakers, et al., 1984)

Wedge-tailed eagles inhabit the majority of Australia's terrestrial biomes. They are found in savannas, forests, rainforests, and mountainous regions, though they demonstrate a preference for more open areas such as woodlands or grasslands. Elevation ranges from sea level to 2000 meters. (Australian Museum, 2003; Australian Museum, 2003; Blakers, et al., 1984)

Wedge-tailed eagles are large, dark-colored birds with feathered legs, pale beaks, and a lengthy, wedge-shaped tail. Wedge-tailed eagles are the largest birds of prey in Australia, weighing from 2.5 kg to 5.3 kg. Females tend to be larger, weighing from 3.2 to 5.3 kg (average 4.1 kg), males weigh from 2.5 to 4 kg (average 3.2 kg). Body length ranges from 1.0 to 1.2 meters and wingspan ranges from 1.8 to an impressive 2.5 meters in length. (Australian Museum, 2003; Debus, 1998; Hoskin, 1991; Macdonald, 1973)

At hatching, chicks are covered in white down, which appears more feather-like toward the head. Immature plumage is golden brown or reddish brown with black tails and wing quills. An adult eagle's plumage is primarily dark brown or black with reddish brown patches on the underwings, shoulders, hind-neck, and nape. On average, it takes six years for wedge-tailed eagles to develop adult plumage. Plumage is identical between the two sexes, except that females tend to be slightly paler than males.

Wedge-tailed eagles have monogamous relationships for life; a pair will breed exclusively until one mate dies, upon which the survivor may or may not seek another partner. The mating ritual involves a series of short dives, pulling up from each with a whistle. During the breeding season these eagles become territorial and will defend their nest and the surrounding area from conspecifics. (Australian Museum, 2003; Australian Museum, 2003; Hoskin, 1991)

Breeding takes place from the months of June to August, though there may be a second occurrence as late as October if the eggs are infertile or captured by a nest predator. (Australian Museum, 2003; Debus, 1998)

Nests are constructed from 0 to 73 meters high, the majority being located within tall trees. Others may be found on cliff ledges, hillsides, or the ground, depending on habitat and the amount of human interference. Nests can undergo repetitive use before abandonment, constructed by large quantities of sticks lined with leaves The initial size of the nest is about 70 to 90 centimeters in diameter and 30 to 80 centimeters in depth. If use is repetitive, the nest can grow up to 1.8 meters wide and 3 meters deep. (Australian Museum, 2003; Debus, 1998)

Clutch size ranges from one to three eggs, though on rare occasion there may be a fourth. Average clutch size is two eggs in the subspecies A. a. audax and one in A. a. fleayi. Eggs are laid over a period of 2 to 4 days, and will not hatch simultaneously, as incubation begins immediately after the first egg is laid. (Australian Museum, 2003; Debus, 1998)

Incubation period lasts from 42 to 45 days, the average length being about 43. Incubation begins with the first egg, so the first chick to hatch often has a head start over nest mates. In lean years, these first hatched young may kill nestmates either through outcompeting them for food or through direct aggression. Fledging occurs after 75 to 95 days. Dependence upon the parents continues for an additional 3 to 6 months, after which the fledgling(s) will disperse. Wedge-tailed eagles reach sexual maturity around three years of age, upon which they may begin pairing; actual mating generally does not take place until age six, when full adult plumage develops. (Australian Museum, 2003; Debus, 1998)

Both males and females construct nests, although males take the lead. Only females brood the eggs. The nest, though defended from other wedge-tailed eagles, is left unprotected from other predators. Parents will play an equal role in providing food for their chicks, but will continue to offer little in the way of protection. If a nestling comes into conflict with a nest-predator, it will be most often be required to fend for itself. (Australian Museum, 2003; Frith, 1969)

The longest lifespan of a banded wedge-tailed eagle was about eleven years. In captivity, wedge-tailed eagles can live for up to forty years.

Wedge-tailed eagles are solitary raptors, primarily found alone if they have not yet found a partner. The primary form of motility is flight; they are capable of reaching elevations of 2000 meters. They spend most of their time either perched in trees or in the air, circling throughout their territory with a pattern of arcs and dives to signal ownership. Eagles usually nest and perch in high trees or other structures. (Australian Museum, 2003; Debus, 1998; Hoskin, 1991)

Wedge-tailed eagles occupy an area of about 30 to 35 square kilometers. However, in years when rabbits are scarce, they may live less than a kilometer apart from each other. (Pizzey, 1980)

The calls of wedge-tailed eagles are seldom heard. The normal call, a double-syllable note, is weak for a bird of its size. These birds have different calls used in greetings, territoriality, alarm, and mating. Wedge-tailed eagles also use flight displays consisting of patterns of arcs and dives to signal territory ownership or to court a potential mate. (Frith, 1969)

Wedge-tailed eagles are carnivores that obtain food through hunting and scavenging. They hunt mostly in early morning, just before sunrise. Their primary diet consists of European rabbits (a non-native species in Australia) and other medium-sized mammals, such as wombats, bandicoots, and bilbies. They will also hunt lizards, smaller birds, and sick or weakened lambs. In groups, wedge-tailed eagles have even been known to hunt animals as large as kangaroos. They will often store uneaten food near their nest for future consumption. (Australian Museum, 2003; Blakers, et al., 1984)

As adults, wedge-tailed eagles have no recorded predators. However, as eggs, hatchlings, and nestlings, wedge-tailed eagles are vulnerable to nest predators, since the parents offer little protection to nestlings. In particular, goannas, or monitor lizards (Varanus) are responsible for the majority of nest predation in this species. (Australian Museum, 2003)

Wedge-tailed eagles have a considerable impact on the population of European rabbits (Oryctolagus cuniculus) in Australia. They are top predators in Australian ecosystems. (Australian Museum, 2003)

By preying on European rabbits, wedge-tailed eagles help to moderate the effect of this damaging, non-native mammal on Australian ecosystems.

Wedge-tailed eagles were once thought to prey on farmer's livestock, particularly lambs. However, upon closer look, it was determined that they only prey upon livestock that is dying or weakened from illness, and pose no major threat to agricultural efforts. (Bell, 1956; "Wedge-Tailed Eagle; Aquila audax", 2004)

Wedge-tailed eagles are protected by the National Parks and Wildlife Act, making it illegal to hunt or otherwise harm an eagle in any way. Wegde-tailed eagles were once actively targeted for bounty hunting because they were thought to prey on lambs.

Currently, forestry operations are a primary concern for the conservation of this species, particularly in more arid regions where materials for constructing nests are less abundant.

The subspecies A. a. audax is rated as 'least concern' by the IUCN Red List. The subspecies A. a. fleayi, however, is classified as an endangered species. About 130 breeding pairs remain, and the requirements of living are much more specific than those of their continental Australian and New Zealand counterparts. The primary risk to this subspecies includes illegal persecution, deforestation and collisions with powerlines. (Tasmania Parks & Wildlife Service, 2006; Australian Museum, 2003; Bell, 1956; Debus, 1998)