Hi Rob, can you confirm that this is definitely a nesting site for the Budgies? It seems like it from the photos. If so this would be very significant, as I'm not aware of any breeding records anywhere close to the ACT.
I assume it is a nest, one bird stayed outside the whole time and the other bird stayed in the knot. I saw one bird travel back to the tree from 800m away. It was a large dead tree with many openings.