Pictorial Checklist of Colorado Birds
Bailey, Alfred M. & Robert J. Niedrach.
The Birds of Colorado- Bulletins 37, 44, and 56 [1897-1900]
The Birds of Denver And Mountain Parks
Niedrach, Robert J.; Rockwell, Robert B.
Report Upon Geographical and Geological Explorations and Surveys West of the One Hundredth Meridian:
Wheeler, Geo. M. & John J. Stevenson
An Annotated List of the Birds of Mesa County, Colorado
ROCKWELL, Robert B.
Seasonal Movement and Habitat Use by Greater Prairie-Chickens in Northeastern Colorado
Schroeder, Michael A.; Clait E. Braun
Birds of Colorado
Birds in Western Colorado
Birds of Colorado's Gunnison Country
Hyde, A. Sidney
American Birding Association Field Guide to Birds of Colorado
Floyd, Ted; Photography by Brian E. Small
Illustrations by Brian E. Small
Western Birds Backyard Guide: Bird Watchers Digest Backyard Guides
Bill Thompson III
Ecology of Boreal Owls in the Northern Rocky Mountains.
Hayward, Gregory; Hayward, Patricia; Garton, Edward