Eastern Guide works best in:
- Alabama
- Arkansas
- Connecticut
- Delaware
- Florida
- Georgia
- Illinois
- Indiana
- Iowa
- Kansas
- Kentucky
- Louisiana
- Maine
- Manitoba
- Maryland
- Massachusetts
- Michigan
- Minnesota
- Mississippi
- Missouri
- Nebraska
- New Brunswick
- New Hampshire
- New Jersey
- New York
- Newfoundland and Labrador
- North Carolina
- North Dakota
- Nova Scotia
- Nunavut
- Ohio
- Oklahoma
- Ontario
- Pennsylvania
- Prince Edward Island
- Quebec
- Rhode Island
- Saskatchewan
- South Carolina
- South Dakota
- Tennessee
- Texas (except in west Texas)
- Vermont
- Virginia
- West Virginia
- Wisconsin
Western Guide works best in:
- Alaska
- Alberta
- Arizona
- British Columbia
- California
- Colorado
- Idaho
- Montana
- Nevada
- New Mexico
- Northwest Territories
- Oregon
- Texas (only in west Texas)
- Utah
- Washington
- Wyoming
- Yukon Territory
The most significant biological division in North America is the Rocky Mountains and related ranges, from Big Bend in western Texas to the Alaska Range. If you want a book for a state or province that does not include any of the Rocky Mountains or farther west, you should buy the Eastern Guide (except Texas, keep reading). Each book includes every species expected in the states and provinces that it covers, so, for example, the entire state of Colorado is covered in the Western Guide, and the entire state of South Dakota is covered in the Eastern Guide. The only exception is Texas. Almost all Texas birds are included in the Eastern Guide, and that book would be the best choice for most Texas birders, but a few species common in west Texas are only shown in the Western Guide.
- Hawaii, Mexico, The Bahamas, etc. are not included in the Sibley Guide to Birds