Lisbon is a slightly separate case of its own as there is so much in the 'free' area in terms of 'non-zoo' (including a McDonalds) - so this probably does bring quite a few non-zoo visitors in, but not specifically for animals!
Last time i was there there were more people in the free area than in the zoo itself. This includes the Animax, a theme park for kids who brought lots of money for the place to survive and build better enclousures. I belive the pet cemitery is also free for people who have their animals in there, but this is part of the zoo.
