A Birder's Guide to Eastern Colorado (East of the Continental Divide)
Lane, James A.; Holt, Harold R.
Birds of Colorado Vol. 1 and II
Bailey, Alfred M. & Robert J. Niedrach.
A Birder's Guide to Colorado [Fourth Edition]
Holt, Harold R.
Great Plains Birds
The Red Crossbills of Colorado
Bailey, Alfred M.; Robert J. Niedrach; A. Lang Baily
The Birds of Rocky Mountain National Park
Packard, Fred Mallery
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 in Western Colorado
American Birding Association Field Guide to Birds of Colorado
Floyd, Ted; Photography by Brian E. Small
Illustrations by Brian E. Small