The behavior of the Harpy Eagle is little-known, aside from observations at a few nests, and of a very few accounts of its foraging behavior. Judging by the prey that is brought to nests, Harpy Eagles often hunt in the canopy. The few direct observations of attacks on prey by Harpy Eagles are from the edges of the forest, such as along the edges of oxbow lakes and rivers (e.g., Eason 1989, Peres 1990). This may suggest that Harpy Eagles preferentially hunt along forest edges (Bierregaard 1994), although perhaps most observations of Harpy Eagle attacks are from forest edges because these situations provide longer sight lines for human observers.
Harpy Eagles probably hunt most often by watching from perches in the canopy, then sally after prey, with a rapid and agile attack. In a successful attack observed by Peres (1990), the eagle "appeared rapidly from low over the canopy." Following a successful attack, the eagle often carries its prey to the top of a tree (Bierregaard 1994). If the prey is too heavy, it may be taken to a fallen tree.
As might be expected from the significant differences in size between the sexes, male and female Harpy Eagles differ in the size of the prey that they capture. The reported size range of prey brought to a nest by the female member of a pair was up to 3.2 kg, whereas size of the prey provisioned by the male ranged from 0.5-2.3 kg (Rettig 1978). Similarly, when provisioning the nest, the sexes differ in the size of the pieces of prey brought to the nest. Females return to the nest with items that are estimated to weigh up to 4 kg, whereas the pieces brought by males are estimated to weigh only ca 1 kg.
The Harpy Eagle rarely if ever soars (Thiollay 1984, Hilty and Brown 1986, Ridgely and Greenfield 2001, Hilty 2003). It may perch at forest edge or on a prominent site in an emergent tree (especially while sunbathing), otherwise it usually is found in the canopy.