Starting with the prehistoric animal life of North America, the author swiftly outlines the natural conditions that obtained which led to the extinction of various mammals, reptiles, and birds once native to this continent. He goes on to describe the unnatural conditions that threaten our remaining wildlife -- water pollution, air pollution, diminishing land reserves. A chapter a piece is devoted to animals, birds and insects that stand in danger of extinction today. A final chapter discusses the importance and the methods of wildlife conservation. This subject has been getting increasingly forthright treatment in juvenile books within the last few years. This book is particularly well organized for finding specific information and it reads with ease. It is illustrated in line drawings by the author and with maps and charts. There is a rundown on the wildlife refuges maintained by the U.S and canada. The bibliography is made up of recent and widely available books and magazine articles.