It does very much depend on what animals you want to photograph but the Sigma will certainly get you the range, I used it there myself earlier this year. I also got decent stuff with a 70-200. The Lions can be tricky as you have to photograph them through glass but the Tigers can be good, especially if you take them from the bridge that overlooks the enclosure. The smaller animals can be a lot easier, such as the Meerkats, but the Ring Tailed Lemurs are great as you can actually go in with them (I think it's only at lunchtime though).