What is a bird? To answer that, we must understand how birds are different from all other living things and how they fit into the diversity of life on Earth. This excellent RSPB guide to bird anatomy looks at the avian body, system by system, how it evolved, and how it functions. Chapters explore traits that are unique to birds, including their remarkable one-way breathing cycle, their trimmed-down skeleton, how feathers permit flight, provide weather-proofing and add beauty, and the avian bill