I like the elephant one, the colors are realy nice, it could have almost been shot in the wild.
The first one of the mandrill is ok, but for me shows to much captivity. In zoos, unless you are perposely meaning to get evidence of captivity to convey a mood, you need to get rid of all evidence of captivity, such as bars, plastic bits on trees and just generally unatural things, i know its hard, but it makes shots 10x more effective.
The tiger one, looks like it was shot in very harsh sunlight, looks to over exposed to me, youve got the surroundings ok though, not much evidence of captivity there, the eyes do a look a bit "dead" though, its a pity you couldnt have got a catchlight in there to brighten the eyes up.