Dennis became enamored of wildlife as a youngster in his native Costa Rica. Living in Central America, it is not difficult to see how biology could become the favorite science for any nature enthusiast, as there are several thousand species in the region. He became a tour guide more than twenty years ago and since 1999, has been working as a naturalist onboard expedition ships. He even has a passion for bird sounds and has a collection of them — recently he worked on the creation of a DVD that mixes the piano with the sounds of the birds. His experience and knowledge has taken him to lead people in other countries in Central America, the Caribbean, South America, Europe, Africa, New Zealand, Australia, Russia, Alaska, the Arctic, and the Antarctic. When he is not onboard ships, he travels to remote areas in Central America explaining to young kids how sensitive the ecosystems are where they live.