The will stay. They don't go far from home. If you have dual purpose birds, they aren't as likely to venture over a tall fence, though they might. Usually if they do, they want to come right back! If you have slightly built birds, like a leghorn, they will go over the fence. Very independent guys, those leghorns. Probably will come back, but we lost one of ours this way. The neighbor's dog got her.
Given the top view, I assumed that they were in a brooder (the home for the babies with the warm light and all), but now that you explain, I can see that the birds are bigger than I first saw and this is their coop! It is very nice.
Clip one wing so that they can't fly evenly. They go sideways and can't get any height.
Mahonri, I took some pics tonight. Let me get them uploaded...