The Harpy eagle is the largest and most powerful raptor found in the rainforest, and among the largest extant species of eagles in the world. The upper side of the harpy eagle is covered with slate-black feathers, and the underside is mostly white, except for the feathered tarsi (a bone in the lower leg of birds), which are striped black. A broad black band across the upper breast separates the gray head from the white belly. The head is pale grey and is crowned with a double crest. The upper side of the tail is black with three gray bands, while the underside of it is black with three white bands. The iris is gray or brown or red, the cere and bill are black or blackish and the tarsi and toes are yellow.
Harpy eagles are found from Mexico, through Central America, and into South America to as far south as Argentina. These birds live in tropical lowland rainforests and may occur within such areas from the canopy to the emergent vegetation. Harpies can also fly over forest borders in a variety of habitats, such as cerrados, caatingas, buriti palm stands, cultivated fields, and cities.
Harpy eagles are live in pairs. They are diurnal birds and do their hunting during the day. They prefer to hunt singly in the canopy or sometimes on the ground. Most commonly, Harpy eagles use perch-hunting, in which they scan for prey activity while briefly perched between short flights from tree to tree. When the prey is spotted, the eagle quickly dives and grabs it. Sometimes, Harpy eagles are "sit-and-wait" predators which is common in forest-dwelling raptors; they perch for long periods on a high point near an opening, a river, or a salt-lick where many mammals go to feed for nutrients. On occasion, they may also hunt by flying within or above the canopy. They have also been observed tail-chasing: pursuing another bird in flight, rapidly dodging among trees and branches; this predation style is common to hawks that hunt birds. Harpy eagles use vocalizations in order to communicate with one another. They often produce "uahaaaau...uahaaaau...uahaaaau" while perching or sharp “wheeeee-wheeeee” call when the birds are close to their nest.
Harpy eagles are carnivores and their main prey is tree-dwelling mammals such as sloths and monkeys. They also prey on porcupines, squirrels, opossums, anteaters, armadillos, and even kinkajous, coatis, and tayras. Harpy eagles may also attack parrots and other birds. Additional prey items include reptiles such as iguanas, tegus, and snakes.
Harpy eagles are monogamous and pair-bonds last for life. They breed every 2 to 3 years and pairs build their nests together. Nests are located high up in a tree, usually in the main fork, at 16 to 43 m (52 to 141 ft); they commonly measure 1.2 m (3.9 ft) deep and 1.5 m (4.9 ft) across and may be used over several years. The female lays 2 white eggs and incubates them around 56 days. The male captures much of the food for the incubating female and later the eaglet, but also takes an incubating shift while the female forages and also brings prey back to the nest. After the first chick hatches, the second egg is ignored and normally fails to hatch unless the first egg perishes. When the chick is 36 days old, it can stand and walk awkwardly. The chick fledges at the age of 6 months, but the parents continue to feed it for another 6 to 10 months. Harpy eagles don't reach breeding maturity until they are 4 to 6 years of age.
Harpy eagles are threatened primarily by habitat loss due to the expansion of logging, cattle ranching, agriculture, and prospecting. They are also threatened by being hunted as an actual threat to livestock and/or a supposed one to human life, due to its great size. Although not actually known to prey on humans and only rarely on domestic stock, the species' large size and nearly fearless behavior around humans reportedly make it an "irresistible target" for hunters. Due to these threats, Harpy eagles have become a transient sight in large parts of their range; in Brazil, they were almost wiped out from the Atlantic rainforest and are only found in appreciable numbers in the most remote parts of the Amazon basin.
According to the IUCN Red List, the total Harpy eagle population size is around 20,000-49,999 individuals. Currently, this species is classified as Near Threatened (NT) on the IUCN Red List and its numbers today are decreasing.
Harpy eagles control the population of mesopredators such as capuchin monkeys which prey extensively on bird's eggs and which (if not naturally controlled) may cause local extinctions of sensitive species.