Get your students engaged by asking them a "hook" question before entering the zoo. An example is: How do you get your food? Chances are that most students will answer with "From Mom and Dad" or "From the supermarket."
Tell the class that zoo animals, animals that can be found both in zoos and in the wild, get their food in similar ways. Baby animals get their food from their parents, while parents have to find food. The different surroundings and abilities of each animal likewise affect what it eats and how it obtains it.
Explain to the students that they'll be observing animals in their habitats in order to discover the animals' diets and eating habits. Let them know that they can record as many observations as they like.
Go to the zoo! If you don't have access to a zoo, plan a "virtual field trip" and show your class images and videos of animals that are typically found at the zoo.