With more than 10,000 species that vary in size, use diverse habitats that extend across latitudes and altitudes, consume a wide variety of food items, differ in how they fly (or not), communicate, and reproduce, and have different life histories, birds exhibit remarkable variation in form (anatomy) and function (physiology). Our understanding of how natural selection has generated this variation as birds evolved and as different species adapted to their unique circumstances has grown considerably in recent years. InIn a Class of Their Own: A Detailed Examination of Avian Forms and Functions,...