This just in from Mrs H. ....."As I walked up the track in the distance I could see two owls - one bigger than the other. The smaller one was bobbing and weaving; this was the best photo I could get. I then walked along the road to try and get something better. By this time there was only one big owl who screeched at me a couple of times before flying off.
There had been no hissing from the box, but there was when I came back. Perhaps the youngest has fledged and the two I saw was an adult giving the younger one some mouse catching lessons. There's now hissing from the box, it probably wants to make sure it gets some dinner."