The male Allen's hummingbird (Selasphorus sasin) is reddish-brown with a green back and head and an orange throat. The female and immature males lack the orange throat. Allen's hummingbirds are very similar to the rufous hummingbird (Selasphorus rufus), except that the male rufous usually does not have a green back. The female rufous and Allen's are virtually indistinguishable in the field. Another way to tell the species apart is by their range. Outside of migration, their summer ranges do not overlap except in the extreme southwest of Oregon.

The Allen's migrates earlier in the fall than the rufous. Adult males leave the breeding ground half a month before the females. Young males are the last to leave. They depart the breeding ground one month after the adult males. Casual vagrants have been seen in the eastern United States.

Allen's hummingbirds live in wooded or brushy canyons, parks, gardens, and mountain meadows. The birds breed in chaparral, thickets, brushy slopes, oak woodlands, well-wooded suburbs, and city parks.

The mating display of the Allen's consists of the male flying in a J-shaped arc in front of the female. He makes a prolonged metallic buzz at the base of the arc. This is often preceded by a back and forth pendulum flight.

The nest is in a tree, shrub, or vine. Nests are often clustered. The nest is built by the female. It is a neat cup made of green mosses and plant fibers and lined with plant down. The outside is camouflaged with bits of lichen held together with spider webs. The nest is able to stretch as the young grow. It takes 8 to 11 days to construct the nest. The female may recondition and reuse an old nest.

Typically two white eggs are laid. The female incubates the eggs for 17 to 22 days. The female feeds the young. The young are fledged in about 22 to 25 days.

Allen's hummingbirds have adapted fairly well to residential areas. As is typical of hummingbirds, they are attracted to tubular red flowers but will also visit flowers of other colors. The birds also eat insects and spiders. The birds will willingly visit hummingbird feeders and like other hummingbirds, jealously guard their nectar sources. If you live within the range of the Allen's hummingbird, put out a hummingbird feeder or plant some tubular red flowers and you may get to see this orange-throated beauty.