Oh, yes, the trap nests--I have looked at those threads quite some time ago. I should give that more thought.
When my girls stopped laying after our cold snap, and then I started finding one egg every three days, I wondered which girl had recovered so quickly. I checked all the vents: all very wide, all very moist. And of course, since they're all of laying age, all their pubic bones are wide (that's something I kept an eye on as they were getting towards laying age). So, the moral of the story, I suppose, is that you can't always count on the vent to provide the answers you need... But thank you, yinepu!