We've all had it happen - leaving our car in a nice park in the shade, only to come back and find a feathered friend, (not a friend anymore) has unceremoniously left a nice white deposit or two on your pride and joys' paint. Funny how this always happens just after you've washed the car as well?
As many people have unfortunately found; if the bird poo is not removed quickly, it can damage and etch into your paint, sometimes leaving serious damage in the most extreme cases.
The reason this happens is that a major part of the poop is uric acid (the white stuff), which depending on what the bird has eaten, can etch right into the paint, sometimes within minutes.