Quite intriguing though. In all my years of observing them in Malaysia, I've never come across a male Common Birdwing or any of the related species in the genus Troides puddling. (Maybe I haven't been going to the right places!)
Then John Moore from up north from where you are, goes and shoots several shots of T helena and T aeacus males happily puddling away in the mountain stream banks of Chiangmai. :hmmm:
I wonder if there are geographical behavioural differences amongst the species/subspecies as well. :thinking: