well always had a problem with bird droppings on both 8P A3's ive owned... but recently had a strange occurence.
Had some on the roof - poss been there a few hours - cleaned it off, leathered it dry and definately seen an 'etching' in the paint. Weather looked bad so didn't bother polishing to try and improve. Few days later had another look and the marks had disappeared and the paint was perfect! - explain that one!