My husband threw together a coop without looking into it too deeply. The problem I have is that the girls prefer to go up to the nest boxes to sleep and avoid the perch. I usually have to go and lift them down into the perch area or they will poop where they lay. I have 3 Brown Shavers, about 24weeks old. The perch is made from 2x4" timber. Do you think this is normal, a design fault, or a behavioural problem? What should I do about it?