For now, the 'Requires' field is the item required to learn this mount, so that's why it's the whistle. Having the Movement parameter go off of Flying is certainly an idea for changing the default music for every other mount, so I'll mention that to the admins and see what they think.
As for the I Believe I Can Fly thing.. I'll look into adding another field on the sidebar so that people don't have to look in the 'Notes' section to see what its requirement is to fly, so hopefully people won't be as confused!
Thanks for the post :D And this isn't too bad of a Necro, lol. Had someone post on a 3 year old comment several times, so this is nothing :)