Hey darren, I had the same the other day mate. (well maybe not the exact same)
I was going out and as I got to the car I noticed the biggest sloppiest bird cack all over the front wing (of the car, not the bird)
(the bird was long gone) (I think....it may well have been watching....laughing to himself, or herself)
The poop was all translucent in colour (well it looked like milk, but believe me it didn't taste like milk)
but as it was pi$$ing it down I thought I would leave it on till I got back. I didn't want to get wet. (it would just make the bird laugh even more)
When I returned home it was still raining hard so I left it. 99% of it had washed off anyway
The next day I cleaned the car. After cleaning/drying/using the Megs ultimate detail spray I noticed that where the poo-poo had been, there were what looked like watermarks.
They took some shifting too I can tell you.
just thought I would share.