We a a rather large dollop of bird poo on the roof of our Golf once. I didn’t wash it off for a couple of weeks and when I did, it had burnt through the top coat of lacquer. Now, if I see a dollop on the A3, I’m straight out there with a soaking rag and leave it to soak for a bit before pouring warm water over it to remove it.If the birds in the trees don't get you, the sap will. Can be quite difficult to shift from car paintwork.