The largest and most ferocious of the world's eagles, the Harpy is a bird that is rare and infrequently seen.

It is the top predator in the jungle canopy, and hunts by day. It is a heavy bird in flight, with a powerful bill and talons. Its wings are rounded, strong and relatively short, and its tail is long: a body shape that makes it agile and highly maneuverable in flight, and enables it to chase monkeys through the canopy branches at high speeds. Its mottled gray plumage provides good camouflage.

Hunting mainly in the canopy, it can swoop down through the tree crowns and with outstretched giant talons capture fleeing monkeys, or snatch sleeping sloths.

Harpy eagles nest in the tallest emergent trees, often silk cotton trees; the nest is a large platform of twigs that is used from year to year. Normally, two eggs are laid, but only one chick is successfully reared to adulthood, in about 6 months.

One pair of harpy eagles that were carefully studied by scientists was found to prey mainly on two animals: sloths and capuchin monkeys. Other animals caught and eaten included opossums, agouti, small deer, tree porcupines, kinkajous, howler monkeys, snakes, ant-eaters like the tamandua, and large parrots.