A comprehensive field guide that uses an innovative Sound Index to allow readers to quickly identify unfamiliar songs and calls of birds in western North America.  Bird songs and calls are at least as important as visual field marks in identifying birds. Yet short of memorizing each bird’s repertoire, it’s difficult to sort through them all. Now, with the western edition of this groundbreaking book, it’s possible to visually distinguish bird sounds and identify birds using a field-guide format.   At the core of this guide is the spectrogram, a visual graph of sound. With a brief introduction to five key aspects—speed, repetition, pauses, pitch pattern, and tone quality—readers can translate what they hear into visual recognition, without any musical training or auditory memorization.   The Sound Index groups similar songs together, narrowing the identification choices quickly to a brief list of birds that are likely to be confused because of the similarity of their songs. Readers can then turn to the species account for more information and/or listen to the accompanying audio tracks available online.   Identifying birds by sound is arguably the most challenging and important skill in birding. This book makes it vastly easier to master than ever before.