I think the metal of the car first goes through an acid corrosion, followed by an electrochemical corrosion. First, the uric acid in bird poop corrodes with iron: 2Fe+C5H4N4O3 -> C5N4O3Fe2+2H2. Then, after the acid is used up, the moisture in the poop participates in an electrochemical corrosion(?). Can someone explain what exactly happens electrochemically?
And please correct me if any of my conclusions were wrong, as I mainly used my own limited knowledge and guessed. I am confident that there is some electrochemistry involved though.