in this game, the animals arent as picky. just look at the part where it has the exhibit part in the main part of their control panel. (a rock with trees i think) note: green is bad! the more empty the square, the better the exhibit. if you go into the zookeeper recommendations, they wont tell you exactly what to put in, but some of the things the animal likes. usually they are just happy if they are in their favorite biome. they can be happy without trees or rocks, but i usually just put a couple in to make it seem more life like.
also check the zookeeper recommendations to make sure you have: shelter, enrichment (stimulation), and food/water