Actually 100mm (or 160mm with APS-C conversion) is too short for most cases. The tiger enclosure is definitely too far for your lens to get a close shot of the animal. Your best bet is at the Fragile Forest enclosure where some of the birds and animals are relatively close.
Anyway, since you only have 100mm just got ahead and use it for the experience. If you can get your hands on a lens that is between 400mm to 600mm is a better choice. A long zoom will give better flexibility.,