Wedge-tailed Eagles are monogamous and apparently mate for life. If one bird of a pair is killed, the survivor will find a new mate. Established breeding pairs are territorial and live in the one area throughout the year, defending around their nest sites from other Wedge-tailed Eagles. (They are also known on occasion to attack intruding model airplanes, hang gliders, gliders, fixed-wing aircraft and helicopters.) Surrounding the territories are large home ranges in which the birds hunt for food but do not defend. There is usually overlap between the home ranges of two or more breeding pairs and of non-breeding birds.
The nest is a large structure of dead sticks, usually reused for years, often reaching considerable size. Nests 1.8 m across, 3 m deep and weighing about 400 kg are known. Nests have a shallow cup on the top, lined with fresh twigs and leaves. Sticks are added by a bird while it stands in the nest. If these sticks are dropped outside the nest, no effort is made to retrieve them. Piles of dropped sticks 1.8 m high have been recorded under the nest trees.
The timing of breeding may vary from location to location and from year to year according to the local availability of food. Both parents share in the duties of nest building, incubation and feeding of the young.
A clutch consists of white eggs measuring 73 mm x 59 mm with varying amounts of reddish brown spots and blotches. These are laid at intervals of two to four days. Incubation starts with the laying of the first egg. Because of the intervals between laying, the eggs do not hatch simultaneously. The first chick hatches larger than the second, which in turn is larger than the third. Survival rates of the chicks vary considerably depending on local conditions, including prey abundance and the amount of disturbance. A breeding pair usually rears only one young per clutch, although in a good year, two chicks may fledge in some nests. Because of the differences in size, the oldest and largest chick has the best chance of surviving. If food is scarce, it will kill and eat its smaller nest mates.
Chicks hatch covered with a white down. For the first five weeks or so, the adults must deliver food to their mouths. After this time they are able to recognise bits of food on the floor of the nest and can feed themselves. The young acquire their first feathers during the second week after hatching. If threatened by predators, the chicks lie flat in the nest, but will defend themselves if required. The adults, in contrast, make little defence of the young. The juveniles remain with the adults for about 11 weeks after leaving the nest. Young and non-breeding birds disperse, moving to wherever conditions are suitable. Juveniles are known to have moved over 850 km in a seven to eight month period.
