My daughters adventure up the mast was due to a largish bird landing on my wind indicator and bending it 90º (not much use if its pointing down ) Interestingly every sail boat in the river had the same issue....
Before this just after I bought this boat I had 3 micro bats that loved to sleep in that mainsail under the covers. I tied a small line around the end to prevent that, but have since moved the boat to a new mooring.
Every area has it's own unique wildlife issues, best advice i can give is look around at the other boats in your area and see what others are doing, and look to see who has the cleanest decks.
I didn't mind the bats, but didn't like the bat poo on my sail.