I am always thinking of ways to deal with sparrows and was pondering this idea. Has anyone ever tried making a decoy of a bluebird (or other bird) head popping out of a fake hole or holes in the side or back of the box? It occurred to me that sparrows seem to attack when the adult is inside the box or has left the box. Perhaps some sort of realistic decoy would discourage them from approaching the box? Perhaps it would confuse them or give the bluebird a chance to get out. If no one has tried this I might try it next year. Let me know.