From page 32 in The Crossley ID Guide: Eastern Birds:
Birds essentially do the same things cyclically, and this includes molting. They do this for a number of reasons. It is important that feathers be kept in good condition to keep the bird warm, dry, and mobile. Of course, some like to look good to attract a mate! Having an understanding of molt and how it affects a bird’s appearance is a large help not only in identifying birds but also in ageing and sexing them.
This stunningly illustrated book from acclaimed birder and photographer Richard Crossley revolutionizes field guide design by providing the first real-life approach to identification. Whether you are a beginner, expert, or anywhere in between, The Crossley ID Guide will vastly improve your ability to identify birds.
This is the first book to feature large, lifelike scenes for each species. These scenes—640 in all—are composed from more than 10,000 of the author’s images showing birds in a wide range of views—near and far, from different angles, in various plumages and behaviors, including flight, and in the habitat in which they live. These beautiful compositions show how a bird’s appearance changes with distance, and give equal emphasis to characteristics experts use to identify birds: size, structure and shape, behavior, probability, and color. Each scene provides a wealth of detailed visual information that invites and rewards careful study, but the most important identification features can be grasped instantly by anyone.