The adult male of the nominate subspecies has a green head and upperparts except for chestnut-brown lores and uppertail coverts.

The tail is also mostly chestnut-brown, giving the species its English name; the feathers' outer webs and tips are bronze green.

The adult female's lower breast is a paler gray than the male's and the scalloping on the throat is more pronounced.

[8] The song is "varied, high, thin, squeaky chirping, tsi, tsi-tsi-tsit tsi-tsitsi tsi-si-si."

A. t. jucunda's maxilla is pinkish brown rather than black; its belly is a darker gray than the nominate's and the bronze green on the tail is narrower.

[9] The rufous-tailed hummingbird inhabits open, non-forested, landscapes such as clearings, gardens, and the edges of forest.

It is extremely territorial and aggressive at feeding sites such as flower patches and feeders, from which it chases other hummingbirds and large insects.

She lays two white eggs in a compact cup nest constructed from plant fibers, leaves, and spiderwebs covered with lichens and mosses.

It has a very large range and a population estimated at more than five million mature individuals, though that number is thought to be decreasing.