Structure, or shape, is a key element to the identification of the family, genus, and species of a bird. The structure of a bird's song and calls is also key to identification. These guides are intended to complement the field guide you carry by highlighting structural differences in shape and sound between the genera and species. They describe how to size the parts of a bird relative to the bird itself. With this approach, you will always have a perspective on the size, shape, and form of a bird, even if it is solitary. Your observations may then be used with the accompanying tables to identify the genus and species of the bird. Waterproof and tear-resistant folded booklets with silhouettes and visual and sound characteristics.