Birds of prey, especially falcons (Falconidae) and hawks (Accipitridae), have extremely (even unusually) sharp eyesight, which allows them to spot prey from a great distance.

Until researchers at Lund University (Sweden) decided to try, no one had attempted to measure the visual (perception) speed of birds of prey. For the experiments (measurements), two falcons were chosen: the peregrine (Falco peregrinus) and the saker (Falco cherrug), as well as the Harris's hawk (Parabuteo unicinctus). Visual speed was measured based on the birds' ocular response to rapidly flashing points on a screen. The hawk's eye stopped responding to two separate flashes at a frequency of 77 Hz, the saker falcon at 102 Hz, and the peregrine at 129 Hz.