Zygodactyl footprints
Most birds, especially perching birds, have three forward pointing toes and one rear or hind toe. Some birds, notably woodpeckers and the Cuckoo, parrots (such as the Ring-necked Parakeet) and owls, have two toes pointing forward and two pointing back. This arrangement is called a zygodactyl foot. So, if you find footprints of a small bird in mud, in most cases (for small land birds), there will be the impression of the three front toes and one back. But sometimes you may see a zygodactyl print. And in most cases it will be a woodpecker. And in most cases of it being a woodpecker, it will be a Green Woodpecker, the largest and most terrestrial of our three resident species.