@BlackRhino: I visited both Indianapolis and Columbus last summer and agree with you that both have excellent elephant habitats with huge pools. I suppose that 4 acres is the gold standard for many zoos, and that 2 acres has perhaps become the new minimum (silver? haha) standard. I'm quite sure that a zoo will never again construct an elephant exhibit any less than 2 acres in North America. Size is not everything, but it is a massive factor for such large and intelligent animals and it is great to see so many 4 acres or more enclosures popping up all over the U.S.