I initially saw the female peering into the hollow where is photograph one below. I suspect the hollow was deeper as she disappeared from my view when I was photographing the Gang-gangs but was back in the cleft of the hollow from nowhere when a jogger calling her dog made some noise. The male stayed on the branch you can see him on in photo two, as well as in the top left of photo three. I am not sure if my attention to their tree made them nervous, as they flew off to the large dead tree in photo four where there was another Wood Duck. Just in case I had disturbed them I left the area. I did not hear any females making their constant call, so they may be breeding now and not wanting to attract attention.
Love that first photo with the female peering out of the hollow. Classic! By the way, do you know if that tree was a Blakely's Red Gum or Yellow Box? Looks like a Red Gum but just wanted to confirm with you.
No worries. Either way, it shows the value of very old woodland trees that provide hollows for native birds. This has just came into effect: https://www.legislation.act.gov.au/ni/2018-536/