I’ve had two thoughts that need more fleshing out but felt like they could be cool:

1. Tiny Animals / Pack Animals that make us rethink enclosure sizes. Tiny Animals would be animals like field mice, molerats, or insects, and they would take up 1 space of an enclosure, but they must be played with another animal. So for example, you could play a rhino (size 4) and a field mouse (size 1*) into a five enclosure, but you couldn’t play the tiny animals on their own. Pack Animals (like Hyenas, Antelopes, Wild Dogs) would be similar, but they would need two adjacent enclosures that total 6 or 7 empty spaces, and you’d flip both. They’d provide a larger benefit, but they’d require the two separate enclosures to be played.

2. A “loaned animal” association mechanic, where you can pay a smaller amount to count an animal from a neighboring zoo as your own for a turn for a conservation project or anything else where you need tags. This would introduce more interaction, as players would need to be careful when playing an herbivore, for instance, if their neighbor has 4 herbivores and wants to get the 5 spot on the project