how long did the crap site on your car before you washed it?
Unprotected paint/ clearcoat WILL be damaged by the baked-on poo as the acid content is apparently too high.
A birds droppings are very acidic (pH 3.5 to 4.5). When bird droppings fall on your paint, the acid begins to burn and etch the paints surface. The longer the bird droppings remain, the greater the damage.
The result of bird dropping damage is a dimple in the paints surface, often as large as an inch or more in diameter. This damage is permanent, but can easily be repaired.
The only way to repair the damage caused by bird droppings is to polish the paint. You must use the polish to blending the surrounding paint, bringing it down to the same level as the damaged area. This may sound drastic, but it works very well. The only concern is that youre making the paint thinner. So you must be careful not to polish all the way through to the primer. Do so, and youll have a more noticeable problem than what the bird left behind.
Any good paint polish can be used to fix the damage with a fair amount of rubbing. Ive found that its better to start with a mild compound, as you would find in a scratch remover (Eagle One Scratch Remover is a good example), followed by a good hand polish.
While its not really possible to keep birds from bombing your car with their dirty little surprises, you can take steps to limit the damage. The most obvious protection is a car cover (please, not while youre driving). But, even the cover wont help you when youre driving. To limit the damage when you get hit, you need to remove the offending slim as quickly as possible. Dont wait. Get it off of your car.
Ive found the best way to clean up after a bird is with a good detailing spray and a cotton terry cloth towel. As Im a clean car fanatic anyway, I keep a little detailing kit in my trunk. It holds a spray bottle of quick detailing spray, a couple towels, and my favorite rubber and vinyl dressing. Thats all it takes for me to keep the car looking great. When a bird gets me, I spray the bird droppings with a few shots of detailing spray and wipe it off with the towel, turning the towel as necessary to keep a clean wipe on the car.
Another way to protect your paint from bird damage is to keep your car waxed. While a standard carnauba wax offers limited protection against a juicy attack, it makes cleanup much easier. Acrylic polymer sealants protect a little better against the harsh acids, but its not enough to create a damage-free barrier if the bird poop sits too long. You still need to remove the mess as quickly as possible.