Have now discovered that there are European Goldfinches nesting on the farm. Didn't think to bring my field guide to Australian birds with me, so thank goodness for Google. Am happy now that I have observed these birds over a period of a couple of days that this is what they are. They are so quick, and shelter within the shrubs so it has been impossible to get a photograph of them. There is a particular clump of shrubs adjacent to a small tree they like and we have seen them come and go. An incredibly intrusive mynah also inhabits this space and scares the finches off on whim.....annoying to say the least. That said, it was the persistence of the finches that made me watch them long enough to reveal that their interest in this territory is related to nesting.
The pair of finches cover each other, and watch until its safe, then take it in turns to disappear into a crack in the old bake house wall. Incredible given it really is only the smallest of spaces. The birds fly to the gap, then have to squeeze in tight as they hop through the crack and into the gap beyond. I can only imagine that the space opens out further inside and they have built a nest within. The bake house is an original building on the property, just across from the farmhouse proper and as such dates from around 1900. The main part of the structure is timber, but the section the finches are accessing is sandstone and forms the external wall of the original bakers oven. Apparently you can still access this via the oven door from within the bake house but in the interests of not disturbing things I have left things as they are. I did however spend a pleasant half an hour in the late afternoon sunshine watching the finches as they took turns coming and going tending to their business.