The ancestral breeding range of Cattle Egrets (Bubulcus ibis) probably was Africa where the species evolved to exploit a foraging niche in the terrestrial-aquatic ecotone, later entering into its well known association with large ungulates (Siegfried 1978). The species’ ability to colonize new areas and its range extension through the western hemisphere have been well documented (Blaker 1971, Browder 1973, Crosby 1972, Davis 1960, Hancock and Elliott 1978, Lint 1962, Meyerriecks 1960, Siegfried 1978). Cattle Egrets were first noted in the continental United States in the 1940s (Palmer 1962) and generally have extended their range inland from coastal regions (Ogden 1978). Our observations plus those of others who have reported sightings of Cattle Egrets in Colorado to the Colorado Field Ornithologists have allowed us to summarize, on a smaller scale, the range extension of this species along the four major river drainages of the state, from the first reported sighting to its present status as a breeding bird (Kingery and Graul 1978). The Arkansas, Colorado, Platte (South Platte), and Rio Grande rivers have at least a large part of their origins within Colorado.