Hello Susan, I know that they will inspect boxes to see which one they would like to nest in, but if you have seen them take in material they are obviously going to nest. It could well be that she has started to lay her eggs and as they lay many the parents will come and go and she will not sit on them until she has finished laying so that they all hatch together. They can go away from morning and not come back until evening. Hope you will see babies.
Hi Catlady, thanks for the info, I saw female enter the box late last night, so you may well be right. Keeping an eye on them today..