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Aquila audaxwedge-tailed eagle

By Matthew Jones

Geographic Range

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)

Habitat

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)

  • Range elevation
    0 to 2000 m
    0.00 to 6561.68 ft

Physical Description

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.

  • Sexual Dimorphism
  • female larger
  • sexes colored or patterned differently
  • Range mass
    2500 to 5300 g
    88.11 to 186.78 oz
  • Range length
    1.0 to 1.2 m
    3.28 to 3.94 ft
  • Range wingspan
    1.8 to 2.5 m
    5.91 to 8.20 ft

Reproduction

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)

  • Breeding interval
    Wedge-tailed eagles breed once or twice per year.
  • Breeding season
    Mating typically occurs from June to August; however, if eggs are infertile or taken by predators, these eagles may attempt breeding as late as October
  • Range eggs per season
    1 to 4
  • Average eggs per season
    2
  • Range time to hatching
    42 to 45 days
  • Average time to hatching
    43 days
  • Range fledging age
    79 to 95 days
  • Range time to independence
    3 to 6 months
  • Average age at sexual or reproductive maturity (female)
    3 years
  • Average age at sexual or reproductive maturity (male)
    3 years

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)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
  • pre-independence
    • provisioning
      • male
      • female

Lifespan/Longevity

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.

Behavior

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)

  • Average territory size
    30-35 km^2

Home Range

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)

Communication and Perception

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)

Food Habits

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)

  • Primary Diet
  • carnivore
    • eats terrestrial vertebrates
  • Animal Foods
  • birds
  • mammals
  • reptiles
  • carrion

Predation

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)

  • Known Predators
    • goannas or monitor lizards (Varanus)

Ecosystem Roles

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)

Economic Importance for Humans: Positive

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

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

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)

Conservation Status

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)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Matthew Jones (author), Kalamazoo College, Ann Fraser (editor, instructor), Kalamazoo College.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

carrion

flesh of dead animals.

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

keystone species

a species whose presence or absence strongly affects populations of other species in that area such that the extirpation of the keystone species in an area will result in the ultimate extirpation of many more species in that area (Example: sea otter).

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

References

Zoological Parks and Gardens Board of Victoria. 2004. "Wedge-Tailed Eagle; Aquila audax" (On-line pdf). Accessed November 15, 2006 at http://www.zoo.org.au/education/factsheets/bir-wedgetail_eagle.pdf.

Australian Museum, 2003. "Wedge-Tailed Eagle" (On-line). Australian Museum Online. Accessed October 15, 2006 at http://www.amonline.net.au/factsheets/wedge_tailed_eagle.htm.

Bell, A. 1956. Common Australian Birds. London, England: Oxford University Press.

Blakers, M., S. Davies, P. Reilly. 1984. The Atlas of Australian Birds. Carlton, Victoria: Melbourne University Press.

Debus, S. 1998. The Birds of Prey of Australia: A Field Guide. Australia: Oxford University Press.

Frith, H. 1969. Birds in the Australian High Country. Sydney, Australia: A.H & A. W. Reed.

Hoskin, E. 1991. The Birds of Sydney. Australia: Surrey Beatty & Sons Pty Limited.

Macdonald, J. 1973. Birds of Australia. London, England: H.F. & G. Witherby LTD.

New South Wales National Parks & Wildlife Service, 2004. "Wedge-Tailed Eagle" (On-line). Native Animal Fact Sheets. Accessed November 16, 2006 at http://www.nationalparks.nsw.gov.au/npws.nsf/Content/The+wedge-tailed+eagle.

Pizzey, G. 1980. A Field Guide to the Birds of Australia. Princeton, New Jersey: Princeton University Press.

Tasmania Parks & Wildlife Service, 2006. "Wedge-Tailed Eagle, Aquila audax" (On-line). Wildlife of Tasmania. Accessed November 16, 2006 at http://www.parks.tas.gov.au/wildlife/birds/wteagle.html.

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