The imaginary trading Guild who inhabit this ever-growing structure use pigeons for info transfer. Seemed a reasonable hypothesis for the period.
We already have one pigeon in residence on an inner window ledge but as they require a more formal nesting/tidying away place, some sort of coop/cage was needed. I’d spent some time looking at ready mades and wondering how I could butcher them to fit the silly space chosen for the arrangement.
Today I built one. Well, one side of one and an opening door with working catch. As it fits across part of the side of the tower and 2 of its windows, it was possible to construct with the one complete face only and use fill ins on the top, which include a random, extra stone.
More pigeons on the way ‘een as we speak.