The nesting tray has been serviced!
Today, the tray was taken back inside the tower and cleaned. After it was poked back through the louvres, it was provided with a brand new layer of gravel. The lack of gravel was probably the reason that last year's breeding season ended in failure.
Hopes are high for 2021. Both birds have been seen on the tower, indeed the male was on the tray just a few minutes before it was serviced.