I could hear wood being ripped and found one of the pair busy tearing a wattle apart.
After a bit more excavation it found its favourite meal, a nice juicy grub, most probably a caterpillar of one of the Cossid moth species.
The wattle that was ripped apart is the Sydney Wattle Acacia longifolia that come up all across our property and are a bit of a weed, so not worried about the damage as I will be taking the tree out. We have lots of these and other trees that the caterpillars favour so there is no shortage of potential food sources for the Cockatoos.
The exposed tunnel of the caterpillar |