first, i would say that any time you have an animal talking in a story, whether it be in the mind or out loud, you have entered cartoon-land.
if it is critical that a speaking character be an animal, then you have to deal with that somehow, and you don’t want to do it right up front, unless of course you want to invoke a disney-like atmosphere.
If an animal that speaks can instead take a human form, then make it human. If you want to throw in some animal stuff, make him have a nose shaped like an eagle, of make him have a pet eagle. But if he is an eagle, then a cartoon is speaking to the reader, and unless you want that effect, just make him/her a person.