In the last twenty years, many careful studies of predation and predator-prey relationships have been carried on by the U.S. Fish and Wildlife Service, by various state conservation departments, and by private individuals and universities. Many of these studies have been carefully planned to work with as many factors as possible under control. In many of them, control areas were established for comparative purposes. As a result, there is a growing mass of information on predation based on something more than opinion or conclusions drawn from isolated observations.