Allen’s hummingbird (Selasphorus sasin) 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 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. SOURCE: Wikipedia
Interesting Fact Aggressive and territorial, male Allen’s hummingbirds will chase any other males from their territory, and have even been known to attack and rout predatory birds several times larger than themselves, such as kestrels and hawks.