I have this issue but not on my car, I have pigeons and crows pooping all over by my pool making a mess. So my solution was to go to my gun shop a request a HUGE favorite from the master gunsmith!!
Attach a scope (an extra I had) attach it to a bb rifle I got a walmart and he calibrated it so it was really accurate bc if they were to sit on the railing I don't want to hit the railing. Its not like I killed them but its been two months and no birds at all!!! Its like touching a hot stove, you are not touching it again!