I'm heading to the San Diego Zoo next week and will be bringing a Canon 80D and the new Canon 70-200mm F4 IS II. For macro shots such as animals behind glass, such as snakes and bugs, would you recommend Canon's 35mm macro, 60mm macro, or 100mm macro?
Which Macro Lens?
Over the next few days, you can trial each of your lenses by bringing them on walks to photograph small objects and critters you encounter. Bring the lens with which you get the best results.
Shooting through Glass
Bring a polarizing filter and tripod/monopod for shots through glass. You do lose light, but the way aquariums and terrariums are lit, even with the lens right up against the glass, you will still get reflections in the shot. There are also outdoor cages where you will be separated from animals by glass.
If you find you don't like the polarizer, you don't have to use it. But if you don't bring one, you can't use it no matter how much you might want to.
With shooting through glass, you'll want to be right up on it if possible to more easily minimize glare. I mean, literally take the lens hood off and shove the front element right up there. Even with chain link, this will help minimize any ghosting, flare, or distractions.
A polarizer may work from further away, but you'll lose a stop or two and that may not be ideal. Bring one if you've got it, but otherwise get close.
I don't have a dedicated macro but use a 12mm extension tube with the 70-200 with good success. But if I could, would use the 100mm macro.
For the San Diego zoo, I'd also recommend the 400 f/5.6 if you can get your hands on it. Good quality zoos like to provide as large of enclosures as possible and I've found that most animals don't enjoy the energy given off by busload after busload of small children - so they will hide out as far away as they can. The 400 will get you there and it's also great for birding, even at the zoo. Bonus - it's a "big lens" and people stay out of your way. Parents will tell their kids even to watch out for you, thinking you are a pro possibly on assignment.