The word "birdier" can be used to describe something that is related to birds or has bird-like qualities. However, if you're looking for other synonyms to better convey your message, there are plenty to choose from. For instance, you could use avian to describe something that is bird-like, aerial to describe something that is associated with flight, or feathered to convey the presence of feathers. Other synonyms for "birdier" include ornithological which pertains to the scientific study of birds or aviary which is a term used to describe a place where birds are kept in captivity. Ultimately, the best synonym for "birdier" will depend on the context in which it is being used.