Have them include information on the collection and preparation of the tracks. They can also report on the animal who made the tracks. Look for tracks in areas where the ground is soft. There can be tracks from insects, reptiles, deer, opossum, pets, etc. Another type of animal sign is scat.
Scientists often identify what type of animals are in the area by noting their droppings.
Animals also leave signs behind when they eat. Insects chew leaves, squirrels and chipmunks may tear cones apart to get at seeds. Some birds peck holes in trees and peck at the dirt to find food. You may want to bring in some examples for the opening discussion. You can set up a desk with an apple that has been bitten and a sweater on the chair back.