Stupid bloody flyscreens!

We have only been here 26 years and we still can't get the flyscreens back onto the windows. Thanks to a friendly bird, who poo'd on the window, I have a question! How do they manage to sh#t through the flyscreen onto the glass? And how do you put the flyscreen back, when it is wider than the window opening! We are not the only ones, I googled our problem and there were heaps of other people in the same predicament! Any answers out there?