The black-breasted buzzard searches for prey mainly while in the air, soaring at medium to low heights across open ground or higher up in woodland treetops. It forages by gliding backwards and forwards across an area, swooping to take prey from the ground or occasionally from trees (3) (4). The main prey items of the black-breasted buzzard include mammals such as rabbits and small rodents, as well as birds, lizards and small snakes, some insects, and carrion (3).
As well as being an active hunter, the black-breasted buzzard is also considered to be an egg-eating specialist, displaying unique behaviour that sets this species apart from most other raptors (7). Preying on the nestlings and eggs of ground-nesting birds such as the emu (Dromaius novaehollandiae), brolga crane (Grus rubicunda) and Australian bustard (Ardeotis australis), a black-breasted buzzard will drive adult birds off their nests by opening its wings in a threatening manner. It breaks open smaller eggs with its bill, or by dropping them on the ground (3).
If the eggs are too thick, like those of large birds such as the emu, the buzzard will either hurl stones at the eggs from a standing position (3) (4), or drop rocks from the air to break the shell (8). Young black-breasted buzzards raised away from adults still exhibit this tool use, proving that the specialist behaviour is innate and not learned. However, the young birds do have to first learn to recognise eggs as a potential food source (7). The black-breasted buzzard is one of only two raptors to habitually use tools when feeding (4). There have also been some reports of co-operative hunting within this species (3).
The black-breasted buzzard breeds throughout its entire range, although it shows a definite preference for some areas. In times of drought it may forego breeding since nesting normally takes place during rainier seasons (5), usually occurring from June until November, and peaking between August and October (3). During the breeding season, pairs of black-breasted buzzards soar over their nesting territory for hours at a time, rising and falling in a display and sometimes performing mock attacks, rolling and parrying with each other. This species is monogamous, and pairs nest solitarily (3).
The nest of the black-breasted buzzard is around 70 to 120 centimetres wide and 40 to 55 centimetres deep, and is built from sticks and lined with green leaves (4). It is placed approximately 6 to 22 metres off the ground, usually in the fork of a dead or living tree branch (3) (4). The clutch size of this species is normally two eggs, but can range between one and three. Incubation is carried out equally by both sexes over a period of approximately 36 to 40 days, and the black-breasted buzzard chicks fledge after 56 to 60 days, after which they remain dependent on the adult birds for around two months (3). Usually only one chick survives and fledges the nest, but occasionally a second chick is also successful (4).
Although normally seen alone or in pairs, the black-breasted buzzard may occasionally gather in groups of ten or so individuals at carrion and communal roosts. (3). It flies with a powerful ‘rowing’ action or, when in pursuit, with rapid, shallow wing beats. Its most characteristic locomotive behaviour is its ability to soar effortlessly, gliding steadily (4) and rocking side to side as it does so (3). Black-breasted buzzards soar in wide sweeping arcs instead of the tight spiralling that is characteristic of most raptors (4).