My pens are fully enclosed. It's just the fence that separates the two pens was big enough for them to get through the other side. I had thought I had wired it together buy I guess I didn't. And that's the part that stinks because there was absolutely no trace of them. Oh well, things happen for a reason!I'm so sorry you lost your chicks.....if it's an open barn a lot of things can get them....snakes, rats(they usually leave a mess though), owls, etc. etc. etc. But, it still sucks when you loose the babies! I hope all the others grow up okay and you don't loose anymore.