Reports the results of 8-year project that surveyed breeding birds of Colorado in 1745 blocks 3 miles on a side, one in each topographic map. Two-page accounts of 252 species that breed in Colorado. Accounts include sections on habitat, breeding, and distribution and include a habitat chart, breeding phenology chart, and distribution map. Short accounts of 13 other species that breed in the state in less than five sites. Chapters on Atlas protocol and results, Colorado habitats, post-settlement changes to Colorado habitats, and Colorado ornithologists. Appendices on block results, abundance estimates, cowbird hosts.