There are many bird books.  Many are excellent.  You can't carry them all into the field.  These five are small and easily handled for field work.  You can read about the rest when you get home.

Wyoming Birds Second Edition by Jane L. Dorn and Robert D. Dorn  Mountain West Publishing  Box 1471  Cheyenne, WY  82003  A handy little flat book, packed with information, that fits in your knapsack.

Wyoming Bird Checklist

Wyoming's Wildlife Worth the Watching

Wyoming Game and Fish Commission

Peterson Field Guides Western Birds

by Roger Tory Peterson  Houghton Mifflin Co.

Your main book to carry.

Ducks At A Distance A Waterfowl Identification Guide

Department of the Interior  U.S. Fish and Wildlife Service.

A small flat pamphlet-like book that is most helpful and free to obtain.

Waterfowl Identification in the Central Flyway

Published by the Central Flyway Waterfowl Council

A small flat pamphlet-like book that is most helpful and also free to obtain