I've lived in Chicago for a very long time and for some reason I've never been over to Brookfield Zoo. It may have been because Lincoln Park Zoo is free and it has always given me my zoo fix or it may have been that I didn't have kids and didn't need something to keep them engaged 24/7. Either way, over the summer I spent some time at Brookfield Zoo and was very impressed with the attractions and the animals they have.
The longest lens currently in my bag is a manual focus 135mm f2.0 lens. It's great for portraits but it was a little short for zoo animals. Luckily I have enough resolution on my camera to crop in without loosing too much detail. I would love to buy a 300mm lens to shoot animals and sports but I don't shoot those subjects too often right now. One day I will definitely take the plunge. In the meantime enjoy the shots from the zoo.