Anisodactyly
The most common bird-feet formation, with three toes forward and one toe back. You see this with most perching birds, wading birds, swimming birds, and raptors.
Zygodactyly
A bird-feet formation occurring primarily in…
Those that can move their talons from three in front to two front, two back actually set three in front to show they are relaxed. The kinds of birds that do this are predatory.