Aside from JP1 and 2, the rest of the movies were all shot after other movies such as Eragon (featuring a cgi feathered dragon) and not long after, Guardians of Gahoole (literally the best animated owls to date), there was zero excuse for not rendering feathers. They used the excuse "they're genetically modified to be scarier" as a means to continue with their shrink-wrapped lizard birds. :/