This guide features more than 777 bird species, plus regional populations, found west of the Rocky Mountains. Entries include illustrations -- more than 5,046 in total -- with descriptive captions pointing out the most important field marks. Each entry has been updated to include the most current information concerning frequency, nesting, behavior, food and feeding, voice description, and key identification features. Here too are more than 650 updated maps drawn from information contributed by 110 regional experts across the continent, and showing winter, summer, year-round, migration, and rare ranges.