Yesterday morning Blue Tits made a few short visits to the nest box. In the first section of the video you can see that as a second bird arrives the first one leaves. Several times a Blue Tit leaves with a thick piece of the grass stalks I put in after the Autumn clean out. This is similar behaviour to that seen last year when the bird removed all the wood shavings I had put in the box before starting to line the box with moss.
There seem to be several days between visits. Maybe, as they do, the birds are investigating more than one possible nesting site.