For the last seven years, I've spent a portion of the school holidays doing live shows at some of the nation's best-known zoos. The shows attract thousands, mostly families with younger kids, and most leave with big smiles on their faces. I do however every year receive a number of messages that go something like this: "You're a massive hypocrite. You claim to be a conservationist, to care about wild animals, and yet you endorse institutions that keep these noble beasts imprisoned behind bars." My stance on this criticism - for which I have a certain amount of sympathy - is rather too complex to get across in 140 characters or less, so I decided to offer a more considered response to the ethics of keeping wild animals in captivity.