A possible hollow, or a pair of hollows in two places in the same tree. Photos taken from different angles. I initially saw the male in his hollow before I went to check another hollow, where there was no activity. When I returned, he wasn't visible but a female was stretching and walking along a branch. She made her way to another hollow in the neighbouring fork, and during this time he emerged from his hollow and climbed to a perch up among the leaves. She sat on the edge for a while then went in and sat in the entrance. Neither bird made any sound or seemed to take any notice of the other, so I have no idea what was going on. I didn't see them today.
I poled the hollow in which the Male gang-gang s sitting - it was bare and empty with no wood chip. Both he male and female where sitting on the branch just outside the hollow that the female went into. This hollow is about 10cm higher than the limit of my pole. With two people it may be possible to hold teh pole up and look into the hollow but I couldn't manage it on my own - but this seems to be the main hollow if one is present.