Males unmistakable with a good view. Females are similar to a number of other female hummingbirds, and are best told from the Calliope Hummingbird and species in the genus Selasphorus by their lack of rufous on the flanks and in the tail. Anna's Hummingbirds are larger and have grayer chests, while Costa's Hummingbirds differ only in subtleties of facial pattern and tail pattern. Black-chinned Hummingbird females are not safely separable from female Ruby-throateds except in the hand. Best told from all species except Ruby-throated Hummingbird by call.