Suppose that there is a race of intelligent being (actually not as intelligent as human but it isn't important) with great bat-like wings that let them fly. They are a bit smaller than the average human and have no arms (their arms are their wings). I've yet to decide if they have a beak or a human-like face, but that's not the point. I thought that living in the open spaces of the sky the should talk in a way that let them communicate as far as possible. Turns out that low frequencies travels farther than high frequencies so It seems that they should use very low noise (like the sound a horn makes), but that's strange if you think that birds communicate with very high screech. So the question are
- what's the most efficient way for a animal to communicate as far as possible?
- What system could that fantasy race use?
- Why real birds sound is as it is?
Note that they have bat-like wings but they're not bat (they can see if it is helpful)
Edit: they should be able to hear human speach and produce sound that are understandable to human. They don't need to speak fluently a human language.