I'd flood it with water from a hose, then scrub lightly with a scrubbrush, buff dry with a soft cloth. I know what you mean about bird droppings being acidic and eating away the shine.

My last car was white, and bird droppings would leave pink stains on the car, that I couldnt scrub off. I found that if I left it parked in the drive, rather than the carport on a rainy day, that the rain, removed the stains.

Were it me I would ask at the auto parts store; at an Autozone sort of place.