This is a very difficult shooting situation, so start by lowering expectations: focus, metering, reflections, and motion blur may all be problems.

Best approach:

• Use the widest aperture you have and a high ISO.
• If the animals pause, use the longest shutter speed you can hold steadily.
• A monopod or even a string monopod can help if a tripod isn’t practical.
• Try different positions to find the best-lit enclosure and the least reflective angle through the glass.
• Keep the camera positioned to minimize reflections from the room lights.
• If the subject is mostly stationary, longer exposures can work better than forcing even higher ISO.
• If you can stabilize the camera, a polarizer may help reduce reflections, but it also cuts light, so it’s mainly useful when the subject isn’t moving much.
• Take test shots and adjust exposure from what you see on the camera.
• Be patient and, if possible, shoot when there are fewer visitors so you have more time and fewer stray reflections.

In short: wide aperture, high ISO, careful positioning at the glass, and as much stabilization as you can manage.