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
.
- Biogeographic Regions
- australian
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.
- Habitat Regions
- temperate
- terrestrial
- Terrestrial Biomes
- desert or dune
- savanna or grassland
- forest
- rainforest
- scrub forest
- mountains
- Aquatic Biomes
- coastal
- Other Habitat Features
- agricultural
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.
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.
- Other Physical Features
- endothermic
- homoiothermic
- bilateral symmetry
- Sexual Dimorphism
- female larger
- sexes colored or patterned differently
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.
- Mating System
- monogamous
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.
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.
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.
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.
- Key Reproductive Features
- iteroparous
- seasonal breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- fertilization
- oviparous
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.
- Parental Investment
- altricial
-
pre-fertilization
- provisioning
-
protecting
- female
-
pre-hatching/birth
-
provisioning
- female
-
provisioning
-
pre-weaning/fledging
-
provisioning
- male
- female
-
provisioning
-
pre-independence
-
provisioning
- male
- female
-
provisioning
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.
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.
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.
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.
- Primary Diet
-
carnivore
- eats terrestrial vertebrates
- Animal Foods
- birds
- mammals
- reptiles
- carrion
- Foraging Behavior
- stores or caches food
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.
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.
- Ecosystem Impact
- keystone species
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.
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.
Additional Links
Contributors
Tanya Dewey (editor), Animal Diversity Web.
Matthew Jones (author), Kalamazoo College, Ann Fraser (editor, instructor), Kalamazoo College.
- Australian
-
Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- 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.
- 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.
- 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.
- forest
-
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
- 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.
- mountains
-
This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.
- coastal
-
the nearshore aquatic habitats near a coast, or shoreline.
- agricultural
-
living in landscapes dominated by human agriculture.
- 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.
- 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.
- monogamous
-
Having one mate at a time.
- 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).
- seasonal breeding
-
breeding is confined to a particular season
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- fertilization
-
union of egg and spermatozoan
- oviparous
-
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
- 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.
- diurnal
-
- active during the day, 2. lasting for one day.
- motile
-
having the capacity to move from one place to another.
- sedentary
-
remains in the same area
- solitary
-
lives alone
- 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
- visual
-
uses sight to communicate
- acoustic
-
uses sound to communicate
- carrion
-
flesh of dead animals.
- stores or caches food
-
places a food item in a special place to be eaten later. Also called "hoarding"
- 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).
- carnivore
-
an animal that mainly eats meat
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- acoustic
-
uses sound to communicate
- chemical
-
uses smells or other chemicals to communicate
References
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 .
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 .