How many weeks was that car parked there?
They ARE nasty birds. I keep the population down by making a ruckus when they arrive in large numbers...I keep a large metal pan on the front porch that I bang against the rail when they start congregating to keep them from roosting. They are basically cowards and don't seem particularly bright, as birds go. The noise doesn't seem to deter the other birds very much; in fact some of them learn to ignore it altogether, but the Grackles hate it. There are a few persistent ones though, and sometimes I will leave for a couple of hours and when I return, they've savaged the feeders and really dirtied the birdbath. In fact, when I get home from work, all I have to do is take one look at the birdbath to know if there were many Grackles around. And I never leave my car out of the carport anymore. I can come home for lunch and in 45 minutes have a nasty mess. That's not all Grackles though. I have a lot of birds around.
The owner of that car made a fatal mistake. He washed his car.