This morning, we woke up to an owl in the box again! So perhaps she is interested in this motherhood thing after all. Between 12:30am and 6:05, she visited the box for periods of 1-4 minutes, accompanied twice by Mr. Owl. Finally, at 6:05, she returned for good. She did a good bit of preening, arranging the egg. There doesn't appear to have been a second egg laid.
We saw no food deliveries during the morning, so she must be doing all her eating out of the box. They may both be hunting. One possibility is that he doesn't bring her enough food, so she was motivated to keep on hunting herself. Another possibility is that she is young and doesn't quite understand that she needs to stay put yet. Or perhaps she is just waiting until she is ready to lay a second egg before she ties herself down to incubation. Once she starts incubating, she would be unable to leave the box for any extended period until the young are hatched and large enough to thermoregulate themselves. This was a nice birthday present for me.
Mrs. Owl left at 6:38pm, returning at 7:03. She sat in the doorway a while before Mr. Owl came home 5 mintues later. They then left together, leaving the box empty until 8:14pm, when she returned. She left at 8:28, returning at 9:17, left from 9:21 to 9:27, again from 9:36 to 10:33, from 10:35 to 10:46, and from 10:52 to 12:33am