Bird feet are usually described by which digits point forward. Anisodactyl feet, the common arrangement, have digits two, three and four forward and one back. Zygodactyl feet, seen in parrots, woodpeckers and cuckoos, have two and three forward and one and four back. Trogons are heterodactyl: digits three and four point forward, and one and two point back.
No other living bird order has this arrangement. The functional consequence appears modest but real. Trogon legs are short and weak, the birds shuffle rather than walk, and they perch upright for long periods, sallying out to snatch fruit or insects in flight and returning to the same perch.
Nesting also depends on soft material rather than strength. Trogons excavate cavities in rotten wood or in arboreal termite and wasp nests, hollowing them with the bill because the feet contribute little to the work.