Scarlet and Waldrapp Ibis.

A bit of an odd mix!

Only if you see zoogeography as the only driver for mixing species.

From a practical animal-keeping point of view it makes a lot of sense, and the two species make a nice show of ibis diversity.

Good point

Absolutely!

I'm not sure, can't these two species produce some hybrids?

I can't say it's impossible, but I've seen a lot of mixed ibis groups over the years and don't recall seeing a single hybrid.

I would agree with that, (the single Waldrapp is a non-breeding female I believe.)