Piciformes nest in holes called cavities, but how they get the cavities varies. Woodpeckers and some barbets use their sharp bills to chisel out their own cavities in trees. Jacamars and puffbirds tend to dig nesting cavities in softer ground or dirt banks. Toucans colonize old woodpecker cavities or other tree holes, rather than excavate their own. Honeyguides hijack the nests of other birds, laying one egg per nest that will yield a honeybird hatchling that may kill the host hatchlings. Regardless, piciformes tend to have large bills adapted for gouging into things. All piciformes have a special foot with two toes facing forward and the other two backward (zygodactylous), in contrast to the usual bird arrangement of three forward and one backward. Piciformes can often be spotted climbing vertically up and down tree trunks.

All modern birds have bills and no teeth. The shape of a bird's bill says a lot about what it eats, for example whether it specializes in seeds (stout , cracking bill), fish (pointy, spearing bill), or plants (wide, serrated bill). Birds swallow their food without chewing, so it travels to the stomach whole or in large pieces. Bird digestive tracts have some special features for digesting chunky food. A pouch in their throat (the crop), is used to store food to be digested later, or regurgitated to feed the young. An extra, muscular stomach (the gizzard) grinds food up. Birds are endotherms, using heat they make internally to keep warm. While a few species allow their body temperature to drop at night (torpor), a nearly constant body temperature is maintained by most birds most of the time. Continuously making heat requires fuel to burn, in the form of food. So, birds spend a lot of time eating.