Contour feathers are not distributed uniformly on the bird’s skin except in a few groups such as the ratites, screamers, and penguins. The types of feathers in birds (many birds) emerge from pterylae, or feather-producing skin tracts; between the pterylae, there are apterylae, or feather-free skin regions (or apteria). Filoplumes and down can arise from the apterylae.