I asked Sal about bird doo once, and he said that speed is the most important thing in removing bird doo. As you know, it is an acid, and it will eat through the Zaino, then through the clear coat, then eat into the paint.
Coats of Zaino help, and will slow it down.
I don't think anyone can say if the damage has been done, but if you wash it carefully with z7 and then apply z6 onto the area and you cannot see any residual pattern of where the dropping sat, then you are OK. If you can see the pattern even after that, then I don't know what to do to remove it. You may need to use a light abrasive or scratch remover.
Finally, be careful in removing bird droppings, as they contain gravel, which will scratch the paint if you just rub it around with a wet cloth. Get it wet first, let it soak, then remove it as carefully as you can. I use a Z7/water mix in a spray bottle, then use the hose and get as much as possible off the car without touching it. (Which is fine with me because it's icky.)