The following behaviour is regularly repeated in the early part of the nesting season. It starts with the male coming to the box and having a good look round, presumably to check that his partner is watching and is going to play her part in the ritual.
Here the male is hanging on to the nest box hole and checking for his mate.
When he has satisfied himself that all is well, he goes into the nest box.
Once inside, he doesn't very often spend much time looking around - after all, he has seen it all before and checking that this is suitable as a nest site is the female's job.
He pops up onto the entrance hole to see what has become of his partner.
"Where's she gone now?"
Instead of flying off again, or dropping back down to the floor of the nest, this time he squeezes out of the hole and stays clinging on to the edge of the hole. Perhaps the female is around but not coming to the nest box and he is doing this because he hasn't given up hope yet of persuading her to come to take a look.
Five seconds later, he goes back inside the nest box.
Here he is again on the floor of the box.
Again she does not follow along behind him and enter the nest box. He therefore goes back up to the nest hole and has another look for her. I wish we were recording sound at the moment as I expect he is also calling to her!
Eventually he must have had some response from the female as about 45 seconds later he drops back to the floor of the box.
Suddenly, he crouches down on the floor of the box as far away from the entrance hole as possible. He must have heard his partner immanent arrival.
Yes - success! She has followed him into the potential nesting site!