I believe 7 acres is as big as a zoo should build. I really don't think it is necessary to build exhibits larger than 2 acres as long as the exhibits provide the mental stimulation an elephant needs. At the Miami Metrozoo, where I was today the African elephants have two paddocks. One is 25,000 square feet and the other is 22,000. They can be combined to make one large outdoor yard. Both yards are very grassy and the keeper told me they need to be mowed every other week. All the elephants there are in very good condition and none show stereotypic behaviors except when anticipating going into the barn in the evening. To me this is a good example of a great elephant exhibit that is not that large. I think this shows that zoos don't really need to build enormous exhibits.