National Audubon Society - Field Guide to Birds - Western Region

Introduced in 1977 and completely revised in 1994, these bestselling photographic field guides have become the birding bibles of more than four million enthusiasts. Virtually every bird found in North America is brought to life in a full-color photograph and with textual information on the bird's voice, nesting habits, habitat, range, and interesting behaviors. Accompanying range maps; overhead flight silhouettes; sections on bird-watching, accidental species, and endangered birds make these the most comprehensive field guides to birds available.

Note: the Western Edition covers the Rocky Mountain range and all the states to the west of it, while the Eastern Edition generally covers states east of the Rocky Mountains.