I wish you'd have done a Linux export for this. It'd have made this almost perfect in my opinion.
That being said. This game is beautiful. I had several ideas for a game to make for a music themed game jam. Nothing like this was anywhere near one of them.
This game has great visuals, and soothing sounds. Flying was pretty easy and "collecting" the other birds was neat. I really liked the art style.
I do think the game needs a little more, uh, game though. There should be some obstacles that are tricky to get around, or some enemy birds to dodge or something. There wasn't quite enough to keep me playing after a couple of minutes. I think this has 80-90% of what could be a great game though.