This yard looks kind of large for a White rhino, it looks suitable for an African or Asian elephant, but then again from what I know, White rhinos seem to need more space then other rhino species
Originally the plan, as I understood it, was to build a new White Rhino exhibit in Phase II or III of African Savanna, leaving this space to be used by the elephants full time. Right now the elephants are capable of using this yard, I've seen them in it, but that means the rhinos are off exhibit.
