I think this is going to require a power-washer.
Every time I see bird shit I am reminded of a Cape Cod summer many years ago. Cory and I were at Nauset Beach at Liam's Snack Shack. Cory was waiting in line while I waited by the tables. I was basking in the gorgeous Cape air, when all of a sudden I felt a splat! It was obviously bird shit streaming down the center of my back. I quickly asked the kid at the table next to me for a napkin. He was about 8 or 9 sitting by himself, holding the table while his family ordered their food. I did my best contortionist moves to try and wipe the bird shit off but I only succeeded in smearing it around more. And for reasons I still cannot fathom, I walked over to the little kid's table and asked him to wipe the shit off my back. Just as he was finishing up (it required multiple napkins) his mom walked up. Have I mentioned that I was in my bikini (why didn't I toss on a cover-up to hit the snack shack), definitely glistening with sweat and gobs of non-SPF Banana Boat tanning oil. Awkward.