Thanks for the quick reply!
It seems not to matter how large the initial size of the exhibit is. I have tried the following:
6X10 Striped Hyaena--get message "needs more space" when the number of adult animals exceeds 4 or 5 when having babies
Many different sizes with aardvark
Approximately 10X20 with white rhino, gemsbok, gerenuk, and aardvark (2 each). I got "needs more space" message, but only for white rhino, gerenuk, and aardvark. Gemsbok was fine (presumably because it is ZT).
Approximately 8X8 with African buffalo. I was fine with the first couple, but then got "needs more space" message.
Approximately 8X8 with fennecs and African spurred tortoise. Only the tortoise needed more space (presumably because fennecs are ES).
I've tested lots of MM, ZT, and ES animals--absolutely no problems with any of them but definite problems with all AA animals. I haven't tried the hippo, but could do so.