Well, Chas, the leaf looks like a caterpillar of some sort, but as for the bits of stick underneath, well, reminds me of what white cockatoos do to my African Tulip tree and other things around the place; they take a few bites and then just drop the rest and start on a new one - seed pod usually of the African Tulip tree. Bird damage? When do you find it Chas, early in the morning? what birds are about? any caterpillars? Looks like something is chewing the stems in half and then just dropping the bits to rot! Ummmm, suspect it's a nocturnal something or other. Dunno what else, what about going out at night with a torch, surprising what you can find in your garden at night mate!

Dunno if your still around Chas, but if you are did you ever solve this problem?

Regards
Bill