They do come around despite the banjo.  Most humans won't even do that.   And they come & stand in the middle of the jam looking at us all. 
One day they launched a mission to inspect the stand-up bass.  It sounds funny when ducks nibble on strings.  They ran, too, when they get a good note out of it.
My bird feeders are all near the porch & during practice they are full of finches & a even a bluebird the other day.  There was a line to use the feeder during last practice, and 2 weeks ago a bunch of deer came & stood in the big field & watched us play.  I think it is something about music soothing wild beasts...
 
Maybe everyone should try playing bluegrass for their ducks, too.