Thanks @TZFan A lot of patience/luck. It's a matter of finding a spot on the glass that isn't too mucked up or getting too much glare from the lighting and then hoping that one of the animals decides to go in the right spot to be seen through that spot in the glass. I've had the best luck on the right hand (my right while facing the exhibit) side. You also need a camera that does well in low lighting/can tolerate a really high ISO setting. Over my last few visits I took over 100 shots of these guys and only got a couple that I consider decent.
