Flying bats use sonar (echolocation) to track and intercept moving prey. A particularly interesting problem is presented in the case of fish-eating bats because the prey can only be tracked by sonar when at the surface of the water; at other times it is "invisible" to sonar. This is a project in which the behavior of a fish-eating bat will be investigated as it tracks and intercepts a target that is under the control of the experimenter. The target's velocity, acceleration and path of movement will be varied, as will the amount of time it spends at the water surface. The experimenter will measure the flight path and head aim of the bat, where it dips its feet in attempting to capture prey that has disappeared beneath the surface, and its ability to resolve differences in velocity of targets moving across its path. The study will also address the role of learning in the bat's development of tracking behavior. The project is important for a number of reasons. The general issue of how animals use sonar for obtaining information and how they process that information to intercept moving and periodically disappearing targets is significant to understanding basic aspects of animal behavior, particularly of bats and marine mammals. It also offers the possibility of suggesting improvements in man-made sonar tracking devices.