Bats hunt a variety of prey. Some bats are insectivores, capable of catching their prey on the wing. Vampire bats hunt for large, slow-moving organisms to use for sustenance. Fruit-eating (frugivorous) bats are adapted to finding ripe fruit distributed throughout the forest. Depending on the food type, bats may rely on their sight and/or echolocation to find their prey. In echolocation, bats emit ultrasonic sounds that bounce off the objects around them. These signals are fielded by the specialized folds of flesh on the face and around the ears, allowing the bat to judge the direction and distance of objects. (For more about bats, see the chapter “Aquatic and Land Animal Diversity.”)

Once an animal has located a potential food, it must decide whether to consume or ignore it. In field studies, behavioral ecologists have observed that animals usually select food that will yield the highest rate of energy return for the energy spent “capturing” the food. Very few animals actually eat all of the food they are capable of consuming. This is known as optimal foraging strategy. As an example, crows that live in the Pacific Northwest often find littleneck clams, which they drop on rocks to crack the clams and then eat them. However, the crows do not eat all the clams they locate; they only eat those clams that are larger and thus contain more energy.