I agree with Chris that "sound" is always good. However, some birds speak (e.g. parrots), some sing (e.g. nightingales), and some cry (e.g. doves). When a bird is speaking, crying (shouting with feeling), or singing, then you can say that they have a voice which makes their sound (e.g. cry/song/words).

Usually we say the "sound" of an animal. As in, "The sound of the raven reminds me of horror movies."

The voice of a human, the sound/cry/chirp/squawk of a bird.