This pair seem to be roosting in this Acacia mearnsii stag. (Last two nights at least.) I can't see that the stag would have an appropriate nesting hollow and the Blue Box visible behind, is also unlikely. They may have their eyes on a large old Angophora floribunda up behind our house, which does have good size hollows and has yielded a successful wood duck generation in the past. They may well be jostling with Kookaburras and Brush tailed possums for the accommodation however.