Chester has hatched a chick from their Writhed Hornbills. This is a UK first breeding. Moving the pair to a new aviarty seems to have done the trick.
I suppose we are talking Aceros leucocephalus here (which more regularly is called white-headed hornbill? NOP Veldhoven has another pair and both Paignton and Paphos Bird Park maintain singleton birds (in an ideal world the Paphos bird would be relocated to Paignton and set up a third pairing for the birds .....)!
I will check what Phillipino zoo has bred the species.