Zygodactyl

In biology, the term zygodactyl refers to birds which have "yoked" feet, that is with two toes facing forward and two back. This arrangement is most common in arboreal species, particularly those that climb tree trunks or clamber through foliage.

Zygodactyly occurs in the woodpeckers, parrots and the Hoatzin.

The more normal arrangement, with three toe forward and one back is called "syndactyly".