This species of birds is one of the largest ones: height of an adult bird is up to 2 meters, weight - 60 - 80 kg (female is larger than male). At such sizes the heron has lost ability to flight: its wings are underdeveloped, not more chicken’s ones by size. The increase of size is connected with the adaptation of heron to hunting large ground animals. Having abandoned places of its ancestor’s inhabiting (bogs and rivers), this bird had adapted to life in thickets of high pampas grasses successfully hunting rodents, reptiles and large insects. When rodents began to be increased in size, the heron also "had grown up". The behaviour of a bird had changed also: it became the running pack hunter. It had allowed birds to prey much larger catch, than lone predator can kill.
The body of a bird is adapted to chase and killing of large prey. Legs are long and strong, fingers are short. The beak is especially remarkable: it is long, straight, on edges of its forward part were developed large tooth-like outgrowths, allowing to tear meat or to render serious wounds to chase. Coloring of the body is cryptic, similar to coloring of bittern (Botaurus) feathering. Eyes are large, bird has keen sight and hearing.
At hunting this species of heron applies two basic tactics: ambush and pursuing. Cryptic coloring allows birds to be hidden in grass in immediate proximity to the planned prey then to attack suddenly, when possible catch will approach too close itself. Pursuing catch, herons at first creep to it, using cryptic coloring, and then actively cut the planned prey’s way to herd and drive it, putting wounds (similarly to predators from canine family (Canidae)). Also birds successfully fishing on the rivers and lakes. At appearing of flights of locusts or other large insect species heron are willingly fed with them: having stretched in line, birds walk on a grass and knock down frightened away insects by impacts of a beak.