What a difference 24 or 48 hours can make.  Spanky woke me up several times the other night with his whining, each time I found him wandering, or exploring outside the nest box.  Adjusting the height of the entrance didn't keep him confined for long.  He quickly developed the ability to scramble over the 6 inch barrier.  I think he spent more time out of then in the box during a 24 hour period.  During that same period of time, I only caught Darla out twice.  The rest of the litter was content to simply peer over the entrance at him.  Maybe he was doing advance reconnaissance, because yesterday they relocated themselves from the nest box to Lorelei's bed on the other side of the room.

I guess it's time to put an x-pen in the room for them.