Birdfolk is a broad label representing a loose grouping of various peoples in the Land of Giants. Just as "there's no such thing as a fish" there's also "no such thing as a birdfolk".
The first way most land-dwelling humanoids want to classify or name birdfolk is by their hands and wings. The most familiar and strange concepts to someone like a halfling, used to hands, opposable thumbs, and feet.
Some have wings on their backs in addition to more familiar hands and arms. Others have claws or hands as part of their wings. Others simply interact with the world with their bird-wings and feet.
However, birdfolks distinguish themselves by not only physical characteristics, but their culture and social orderings.
Some birdfolks can dive well and have claws that rip, these are the Hunters. The Wise Ones are more gifted with magic and tend to lack the curved beaks and speed of the Hunters. The Land-walkers are peculiar among the bird-folk as they are large and powerful, and are heavier and either can't fly or just hop short distances.
The social order of birdfolk varies by region and all birdfolk can be found in all societies. Some tend to large flocks, while others prefer private lives. A common theme among most birdfolk cultures is superstition and the belief in a predestined fate. There are those that set out to make their own path but they are less common.
13th Age Stats
Hunters (Hawks Falcons)
+2 STR or DEX
Wise Ones (Corvids, Owls)
+2 INT or DEX
Land-walkers (emu, ostrich, penguin, storks?)
+2 STR or CON
Example images showing the variety one can find within the label of "birdfolk".