In a way, I'm glad that Noah's Ark is finally getting picked on, but I'm misguided - its not for the reasons I would like (and I'm not referring to their religious teachings).
To be honest, this issue has been bubbling away under the surface for some years. In the following Biaza publication, there is a slightly unnerving article on 'animal byproducts', and legislation around 'feeding zoo animals to zoo animals'. It is widespread for dead animals to be used in some other way after their death, or, as I suspect, to be bred specifically to be 'culled' and fed to other species.
BIAZA Public Access
I think its easy to debate whether this is right or wrong, perhaps easier to do if the zoos were state funded US institutions, but they're not, and like it or not, UK zoos know its not really okay to decieve the paying public about where some of their animals go, or what happens to them when they die. As stupid as some folk may think the public are for objecting to stuff like this, they are the financial backers of the national UK zoological collection, spread across its many institutions.
As for circuses, its for governments to legislate, I wouldn't expect zoos to boycott trading with them, although I would expect the traffic to be very much one way, given the public perception of animal circuses.