If you spot two
enormous birds locked together in what appears to be a
soaring, tumbling battle for dominance of the sky, then
look again! You're most probably watching a pair of
wedge-tailed eagles re-igniting their passion prior to
breeding.
By Rachel
Sullivan
Wedge-tail
eagles are among the world's largest eagles with a
wingspan of up to 2.5 metres. They are relatively common
all over the Australian mainland, in Tasmania and
southern New Guinea, except in densely populated areas.
To get off the ground they use
an active flapping flight, but once airborne these eagles
use thermal updrafts to carry them effortlessly aloft and
gracefully spiral upwards to great heights.
Australia has three species of
eagle, the Little Eagle (Hieraetus morphnoides),
the White-bellied Sea Eagle (Haliaeetus leucogaster)
and the largest, the Wedge-tailed Eagle (Aquila audax
- literally 'bold eagle'). Wedge-tails prefer open
woodland, but are found exploiting a range of habitats
from arid desert to grasslands, mountainous areas, and
even rainforest.
Easily identified by their size
(up to 3.2 kg for males and 4.2kg for females),
Wedge-tails are known as booted or trousered eagles thanks
to the heavy feather 'trousers' covering their legs. They
are also characterised by finger-like wing feathers and,
of course, a long wedge-shaped tail. Young birds can be
distinguished by their light brown plumage and golden
highlights; the plumage of older birds tends to darken to
near black at sexual maturity between five and seven
years.
Fiery courtship
According to Dr Penny Olsen, a
research scientist and raptor expert from the ANU,
Wedge-tails appear to be monogamous, mating for life.
"They certainly form long-term pair bonds," she says,
"although if one bird is killed the survivor will take a
new mate."
The time of breeding depends on
temperature to some extent. In Tasmania, Wedge-tails breed
later than their northern counterparts, but all breed
between June and October.
"Breeding season is the best
time to see Wedge-tails because of their highly visible
soaring and diving displays," says Olsen. Males may also
mark their territorial boundaries by flying in a series of
showy descending loops, or 'pothooks'.
In another dramatic manoeuvre
known as talon grappling, two birds lock talons with one
being forced to flip over and fly upside-down, which
although spectacular can be fatal if one bird refuses to
let go. Olsen says the research community is divided on
whether this is an aggressive display aimed at warning off
potential interlopers, or just two birds showing off as
part of their courtship ritual.
...............
Special thanks to Dr
Penny Olsen and Peter Merritt.
http://www.abc.net.au/science/articles/2006/07/06/2041996.htm
