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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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