As some people have mentioned, you might not be able to see any wildlife or learn about the importance of these animals, insects, plants, etc if you do not get a tour guide. You'll notice most of the tour guides carry around a field scope which allows you to be able to see these animals up close. In reality, they are very far and hard to see with the naked eye. We did our tour with Andres, extremely funny, sarcastic, and knowledgable! He even let us know about the Hidden Cove area which is a 20 minute walk from the food area. Be sure you do not miss it as it offers the best views of the beach. You also have the opportunity to bathe on the beach (we caught some monkeys walk around and eating fruit!).
Be prepared to come with DEET bug spray, sunscreen, a hat, and comfortable loose clothing. When we were there, we were soaking wet! (and I hardly sweat...), But, a fun experience nonetheless.