After 20 years we finally succeeded with our bat house. I watched 18 bats leave the house last week. I even was able to get some great video of the little guys. But after several days they have seemed to have moved out of their bat house. What did we do wrong or can you tell us why the appear to be gone or will they return? Thanks in advance.

Congratulations! Sounds like you are doing everything right. Bat houses are great places to stay during the summer and early fall. But in IL, most do not provide enough protection from the winter cold. My guess is that the bats either ran into a food shortage in the local area or they took off early to find good winter accommodations. Keep the box in good repair. They will be back next year.