The light scratches are there as a result of rubbing the bird crap off, not caused by the crap itself - sorry to be so blunt.

To get bird poop off your car - put hot (very hot!) water over the area and leave for 20 minutes, then put a mild soap solution over it and leave it for a few minutes. Then jet wash it or hose it off. DO NOT RUB OVER THE AFFECTED AREA - YOU WILL SCRATCH YOUR PAINT UP!!

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