My user name makes it clear that I am a docent. I volunteer at Reid Park Zoo. We do small animal presentations for the public to meet and touch (skinks, small snakes, hedgehogs, etc), educational stations with artifacts at most of the major exhibits (I only do the cats, lion or jaguar and every once in a while tiger), or just patrol the grounds to answer questions and give directions (and rebuke people trying to feed the animals).
I also do a digital slide show and lecture on the first Saturday of the month. It is a program I put together with my cat photos called "Wild Cats Of The World."
The term "docent" is commonly used for volunteers here in America, not just at zoos but also botanical gardens and museums. I am curious, is it used much in other countries?