At the time, the Solitary eagle (now Buteogallus solitarius) was considered to be a subspecies of Harpyhaliatus coronatus, until phylogenetic analyses of their DNA showed that they are, in fact, sister species.

[2] The Chaco Eagle populations are affected by many threats, including habitat degradation, collisions with human structures, and persecution.

[6] Another important factor is the electrocution of Chaco Eagles by power poles, which also has a sizeable impact on their populations.

[8] Often seen in solitary pairs or small groups of three,[4] the Chaco Eagle is a tame crepuscular species that forages during early hours.

[9][10] But other mammals such as rodents, possums, European hares (lepus europaeus), and lesser grisons (Galictis cuja) are also taken.

Small lizards are caught directly with talons, but large lizards such as red tegus (Salvator rufescens) and Argentine black and white tegus (Tupinambis merianae) are captured by approaching them from the side, grabbing them by the hip with one foot and then by the head with the other, apparently to reduce the risk of being bitten or whipped by the tail.

[4][12][9][11] Normally, this raptor kills or hunts its prey, but some individuals have been seen eating dead deer, sheep, armadillos, and roadkill.

Between August and October, a single white egg with grey spots is laid on a platform-like nest of sticks and leaves.

[4] The female stays near its offspring from the moment the egg is laid until the chick is old enough to be left alone for short periods of time.

The male continuously brings food to the nest, while the female joins the hunting when the chick hatches and grows a bit.