Allen's hummingbird (Selasphorus sasin) is a species of hummingbird. It is a small bird, with mature adults reaching only 3 to 3.5 in (76 to 89 mm) in length. The male 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 throats. Females are mostly green, featuring rufous color only on the tail, which also has white tips. Immature Allen's hummingbirds are so similar to the female rufous hummingbird, 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 part