I would like to clarify that I have no idea whether or not a Shoebill is on-exhibit at Exmoor. It's my understanding based on personal communication that there is, but this may very well not be the case and I encourage everyone to take that with whatever degree of healthy skepticism they see fit. I was just expressing my opinion that if a new arrival is on-show but hasn't been announced officially by the zoo, it's still well within the right of any visitor to report that since the zoo has still chosen to place said animal on-exhibit. Exhibiting an animal is itself a form of official 'reveal' to the public, especially if it's a signed individual (which I also don't know in context of the supposed Shoebill).
Now if someone visits and sees an animal on-exhibit but is either told not to post about it or is aware that the zoo wishes to make an official announcement soon, it does become a sort of grey area. On one hand, the animal is literally on-exhibit and anyone can see it, but on the other, the zoo still wishes it be kept quiet. I still lean towards saying it's fine to post as long as you weren't explicitly told not to say anything because the animal is on-exhibit now, but I can't say I've never kept something to myself even when an animal is visible at a zoo because I've felt it the better thing to do. I suppose in those scenarios, it's up to the individual to make the call.
Either way, I wasn't trying to make any official confirmation of anything, just sharing my opinion based on my understanding of the situation. I apologize for not making that more clear.
~Thylo