I was stuck at 4 1/2 stars for three zoo years. I had built my zoo using no non-endangered species since March, Year 1, and I thought i had done pretty good, buying that many animals within two years. But in year five, I had still not won. I bought many cheap animals, such as gazelles and ostrich, to put in the exhibit with my sable antelope and my elephant. My fame went up after buying just around five more species.
I quickly released those species to the wild, and my fame didn't have time to go down due to the loss of species. The prompt appeared saying I'd won.