Hi Dicerorhinus
There has been natural breeding in Europe but I do not know if there is any natural breeding in Europe at present. But I am not aware of natural breeding at present in San Diego either. I also thought they were going for AI with this species now? The reason I say at present for the captive population in Europe is that it is very inbred (could well die out without new blood) and this was one of the big arguments used by AI proponents incl. Mr. F. Hermans, the famous Belgian pheasant keeper and breeder. No one seems to know much about the few Blyth's in the Middle East and if any of them can be considered pairs. There are also several in China but I'm not sure it is fair to count them in (all three monals are also in captivity in China. They also managed to breed the last monal, the Sclater's in the Beijing Center for Breeding Endangered Animals). There even has been Blyth's claimed to be the molesworthi subspecies in a private collection in USA but I don't know if they are still around or if they in fact were molesworthi as claimed. There are unfortunately also Blyth's strains in Europe and USA with hybrid Satyr blood.
I have had the pleasure of visiting both backstage and in hornbills San Diego has a very impressive collection but like said, not beyond Jurong's. Jurong are not always good at updating ISIS (especially in their southeast Asian species) and how reliable it is can be discussed but it gives an idea about the figures. If limited to African hornbills they are almost equal: Right now San Diego Animal Park and San Diego Zoo combined list 7 species (2 Tockus species, 1 Tropicranus, 0 Bycanistes, 2 Ceratogymna, 2 Bucorvus) and Jurong lists 6 species (2 Tockus, 1 Tropicranus, 2 Bycanistes, 0 Ceratogymna, 1 Bucorvus). When it comes to pure breeding of African hornbills San Diego is more clearly in front of Jurong however.
As said before I do not know how many storks Walsrode have left but at one point they had all stork species except Maguari and with a large portion breeding (for example including both openbills). San Diego have not matched this species diversity at any point.
All this aside - like I said before San Diego's collection is world class and outstanding. No matter where you live - if you are a real zoo fan this is one of the zoos you have to visit at some point.