The Allen’s hummingbird is a small bird, with mature adults reaching only 3 to 3.5 in (76 to 89 mm) in length. The male Allen’s has a green back and forehead, with rust-colored rufous flanks, rump, and tail. The male’s throat is also an iridescent orange-red. The female and immature Allen’s hummingbirds are similarly colored, but lack the iridescent throat patch, instead having a series of speckles on their throat. Females are mostly green, featuring rufous color only on the tail, which also has white tips. The immature Allen’s hummingbirds are so similar to the female rufous hummingbird that the two are almost indistinguishable in the field. Both species’ breeding seasons and ranges are common factors used to differentiate between the two species in a particular geographical area.
The Allen’s hummingbird is common only in the brushy woods, gardens, and meadows of coastal California from Santa Barbara north, and a minuscule portion of lower Oregon. The nominate race of Allen’s hummingbird S.s. sasin is migratory, and winters along the Pacific coast of central Mexico. A second race S.s. sedentarius is a permanent resident on the Channel Islands off southern California. This population colonized the Palos Verdes Peninsula of Los Angeles County in the 1960s and has since spread over much of Los Angeles and Orange Counties. source