Thanks for the advice! I think we will replace the wire on the back vent for sure or at least put hardware cloth on it in addition to the current wire and once that is replaced then I'll feel comfortable leaving it open at night. :)
We bought our chicken coop a week ago and moved our chicks into it on the same day. The coop has a vent in the back with a wire over it that has a door to open it and lock it and also a sliding window in the front with normal window screen. I'm a little too nervous to leave the window open...