I've just been to Chengdu Zoo today and seen these birds and they are definitely hybrid spoonbill x ibis. There are five of them, housed in a mixed aviary with scarlet ibis, demoiselle cranes, grey herons, little egrets and mandarin ducks (and with additional signage for black-headed ibis and black stork, neither of which were in there). Four of them have the long downcurved bills similar to those of normal ibis, but the fifth bird has a half-length bill with a blunt end. I'm not sure if this is a natural formation or if it may have had its bill broken off.
They are large birds (spoonbill size) – twice the size of the scarlet ibis in with them, and only a little smaller than the demoiselle cranes. When they were perched high they resembled American white ibis but when on the ground their body proportions and gait are unmistakeably those of a spoonbill. Particularly when they flapped across the aviary their flight was exactly like that of a spoonbill rather than an ibis. If they had normal spoonbill bills then they would really look no different to black-faced spoonbills.
Three interesting observations:
One: the zoo (at least currently) has no spoonbills of any species, and the only ibis they have currently are scarlet ibis (although they still have signage for the black-headed ibis).
Two: while the bill of the birds is long and downcurved like an ibis (in fact it seemed particularly long), it spatulates out at the end rather than tapering or ending bluntly. It isn't anywhere near as pronounced as a spoonbill's spatula of course, but it is very noticeable.
Three: their feeding technique was a fascinating combination of spoonbill sweeping and ibis probing. There was a tub of water with fish in it, and also a large pool in the aviary. The pool was being cleaned so there was no water in it, but there were loaches wriggling around on the wet concrete. The scarlet ibis were doing the normal pecking-probing action which ibis have, but the hybrids were sweeping the bill side to side while probing at the same time. They did the same thing whether they were catching fish from the tub or when trying to pick up the loaches off the concrete. At the back of the aviary there was food spread on the concrete (grains and greens it looked like) and the half-beaked hybrid was using the same technique to feed here.
My best guess for parent species would be black-headed ibis and black-faced spoonbill (or maybe European spoonbill).
