This is by far the most popular and talked about field trip I ever conducted. Students loved it, parents loved it, the teachers loved it and the docents and visitors to the zoo loved it because the students did their presentations at the animal exhibits. This gave the students a larger audience and guests learned an extra fact or two about the animals.
It can serve as an end of unit project as well as a research project and written report either in 5-paragraph form or a brochure. There are numerous suggestions from flexible implementation based on your needs and suggested lesson plans and scheduling are included.