*ignores Yuna's stomach and drags her back through the woods to bike*
Those musicians are to monsters as sirens are to sailors...only a lot more dangerous. What's interesting is that they only appear when someone wanders into the spring area...but if a monster happens to be near by and can hear it...
Basically, the monster falls into a trance and follow the music into the spring. Usually killing them.
It doesn't affect humans. Even though you are a supernatural being, you are still technically a human, although the spring does have strange properties that makes someone never want to leave...