Lenses: Bring your longest lens and a macro. Use the long lens to get frame-filling shots of distant subjects. If you can place the lens close to the bars they will fall out of focus and be rendered invisible. Be sure your aperture is wide open to obtain this effect. Adhere to the rules of the zoo before attempting this. With your macro lens, get right up to the glass to eliminate reflections and glass glare. The closer your subject is, the better to fill the frame. Shoot in RAW as the image will take on the color of the glass. This cast can be corrected with your RAW editor. If you use flash, be sure the flash is also pressed up to the glass to prevent its emitted light from bouncing back off the glass.
Tripod: Most zoos don’t have tripod restrictions for outside exhibits, but they may set limitations for indoor ones. Before you head out, check into this. A monopod is a good alternate. The tripod will help stabilize your lens and keep your arms from getting over tired as you wait for the animal to display behavior. If your arms get tired and you drop the camera to your side, inevitably, this will be the moment the animal does something interesting. By the time you raise the camera back to your eye, re-create the composition and fine-tune the adjustments, the shot may be gone.
Settings: Pump up the ISO so you can obtain a high shutter speed to freeze the motion of your subject. If the animal is absolutely still and you use a tripod, use a lower ISO to get better quality. As stated above, if you need to defocus a foreground fence, place the lens right up to it and open your aperture as wide as possible. With other situations, if you need more of depth of field, adjust the aperture so the corresponding shutter speed is still fast enough to freeze the movement of the animal.
Be Patient & Be Ready: As with any animal you photograph, it’s better to wait for it to do something interesting or to display emotion. The image will be more intriguing than if the animal just stands there or worse, simply lies down. You may get lucky where the animal does something interesting as soon as you arrive, but more than likely, you’ll need to wait. Be patient, and you’ll be rewarded. This brings to mind another thought. Before you go to the zoo, research the feeding times for each species. In that their biological clocks know these times, they tend to be more active in the hour or so before they’re fed. Coupled with patience is the notion of being ready. If you’re not constantly on the animal, chances are you’ll miss the action. It will be necessary to rest your viewfinder eye every once in awhile, but try to minimize the amount of time if you want to obtain a winning shot.
Go Back: Revisit the exhibits that house the species you want to photograph at different times of day as each nets different lighting angles. If the zoo is open late, note which exhibits get bathed in sunset light and make it a point to be there for the sweet light. Try different times of the year as each nets different conditions. If you live in a cold weather climate, go right after a fresh snow and head to the polar bear, arctic fox, bighorn sheep or other species that make sense.