This idea is dumb, I am the first to admit it, but it would make the game more real, and it would be distinct from other games I think.
Instead of depending on spawns for animals, what if when two animals came within close proximity a third animal would also show up. You could decrease the frequency of animal spawns and make players be more ecologically friendly. This could also develop into new animal types, like fawns when two deers get it on. So, now you can all tell me how this is a dumb idea.
Edit: I forgot to say that because this is a dumb idea, all the good ideas should be implemented first.