Adding on to malicious_angel_82
In wetland exhibits, you can have hippos and flamingoes.
In addition to the ones mentioned by malicious_angel_82, you can put gemsboks in desert exhibits.
In tropical exhibits, you can have chimps, gorillas, crested gibbons, and orangutans.
In addition to the ones mentioned by malicious_angel_82, you can put thompsons gazelles in savannah exhibits.
In addition to the ones mentioned by malicious_angel_82, you can put spectacled bears in temperate exhibits.
When you do combine exhibits, make sure the food, houses, and toys are shared by most of the animals. If an animal has needs that are rare, like the crested gibbons only sleeping on raised platforms and tree trunks, make sure to pick the one that isn't in common with any other animal in the exhibit. This way, they will have access to their specific needs that may otherwise be used by teh other animals.
We have more cheats and tips for this game here, Zoo Tycoon 2: Endangered Species cheats
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