Selasphorus rufus

The extensive rufous in the tail rules out Calliope Hummingbird. The length of the central rectrices (as long or longer than other rectrices) rules out Broad-tailed. Allen's Hummingbird adult female has a narrower outer rectrix, and has not yet been documented in Colorado (but presumably occurs in southward migration). Aggressive behavior towards other hummingbirds also was consistent with Rufous. Adult female Rufous shows some iridescent orange throat feathers and exhibits an indentation in the shape of R2 (second rectrix from center, in the tail feathers). The R2 of this juvenile resembles that of adult female Allen's.