Thanks guys! It sounds as though, just like humans, each individual bird will have different capacities.
This is probably an issue of over-thinking on my part, but that's what I do best (hey, nothing wrong with being precise!). My "story bird" only needs to say a word or two throughout the entire novel, but as someone who has made a study of ventriloquism, I recognize the difficulties in pronouncing certain sounds without the use of the "correct" equipment to do so (namely the lips, which birds don't have!)