I've been broadcasting the Swift Calls CD now for a full week.
I've had the calls playing from between 3 to 14 hours each day, but I had still not seen a single Swift in the area.
However this morning, on the 8th day, which turned out to be a dreadfully damp & dreary, wet, mizzly day, I had taken the player down & rested it on the window sill while I walked my dogs before switching it off & taking it inside out of the wet, when the first Swift suddenly appeared!
It flew around the house once, then once around my 1 acre paddock before headed South, without ever going near my boxes.
Hopefully the next one will stay a little longer & be just a bit more curious.