Two immature male Gang-gang Cockatoos started in one tree but then they went to a tree that is usually used by Sulphur-crested Cockatoos for breeding. One of the Gang-gangs, stuck his head into the hollow the Sulphurs use and that brought an immediate response from the Sulphur that was in the hollow. The Gang-gang wisely withdrew to a branch further away. There were then a Gang-gang on a branch either side of the hollow. The Sulphur went back into the hollow after a few minutes leaving the Gang-gangs to join each other on a single branch.