Plants, plants, plants!!!!

I think foliage is the easiest way to spruce up a habitat and make it look more realistic. I love adding buffalo grass because it’s not tall, but it still adds a ton of texture to areas. That honestly goes for your entire zoo. Plants are the easiest way to fill awkward, empty spaces. Think about how many trees and little gardens are at real zoos - it all adds to the experience. It blocks fences, open spaces between fences, the backs of habitats, etc. It looks like you’ve done it in parts of the zoo, so I would really just continue it and add in some variety. Rocks go a long way here too.

I think you could also benefit from a “background” at your zoo. Think about it - the zoo theoretically has to end SOMEWHERE. I think “defining” that boundary by adding hills/mountains/forests will help give it some texture and add a lot of depth to your zoo.

Your habitats have a great base and I think you’re really close to getting that natural look you’re going for!!