Not that it solves the problem but if you parked forwards rather than reversing in at least the crap would be on the back of the car and you could still drive off straight away if needed.
Also have you tried scaring the birds off? (Bird deterrents)
Speaking of tyre noise, I very nearly got a Cupra 300 ST recently on contract hire, and then got an E Class Estate instead.
It's coming on Thursday ...
Might work might not - a "realistic" animated owl sitting on that ledge above the door might work - but sometimes it doesn't work at all.