Very similar to female Costa's Hummingbird, which would be a vagrant in Colorado. Buff on flanks and spots on throat are obscured by fuzzy focus of this photo. The shape of the primaries, especially the obvious difference in width of the 4th and 5th primaries, confirms the identity as Calliope (thanks to Sherri Williamson for pointing out this important identification feature). Costa's primaries are narrow with no obvious difference in width of the 4th and 5th primaries.