What adaptations of the harpy eagle allow it to be such a successful rainforest predator?

The ranking of most eagles in the food chain is at the top. They are called apex predator.

The harpy eagle is one of the largest eagle there is. Common to most eagles are its sharpness of their vision. Most eagles use it to sight their predator while circling above the ground at a distance unseen by the prey. However, harpy eagles adapted a way of hunting prey which is called perch-hunting.

Perch-hunting is a way of looking for predator by scanning the trees for prey by flying in short distances from a tree to another tree. The harpy eagle developed this skill since it is hard to sight a prey in a rain forest because of the leaves and trees blocking its vision. Hence, perch-hunting is very apt for the scenario of a rain forest eagle.