I used to have a real problem with dirty nest boxes. The birds would much rather sleep in them then on the roost. It got pretty bad with several hundred birds, and about 50 nest boxes. Here is what I came up with. I wanted to share it in hopes that someone else could use it. On the perches I laid 1" by 6"s I then screwed a little wood hook onto several nest boxes. After I gathered the eggs in the evening, I would set the boards in place. It works pretty well. I hope that I am not the only one that had a problem with that. I would set the board into the hooks. The 1" by 6"s just lay on the roost during the day.