[5][8] It is named for John Xantus de Vesey (Xántus János), a Hungarian zoologist who collected the first specimen.

Their forehead is dull brownish and their upperparts iridescent golden green with some rufous edging on the uppertail coverts.

Their tail's central pair of feathers are golden green with a rufous shaft and the other four pairs dark rufous that pales towards the end, a black and bronzy green band near the end, and thin white tips.

The species inhabits arid woodlands of scrub, oak, and pine-oak at elevations between 150 and 1,500 m (490 and 4,900 ft) and also visits coastal desert, gardens, and feeders.

[8] Genetic analyses suggested that female birds disperse more than males, resulting in female-mediated gene flow from north to south.

[9] Xantus's hummingbird forages for nectar at a very wide variety of flowering plants, shrubs and trees, and feeds at all levels of the vegetation.

[8] Xantus's hummingbird breeds between July and September or October in the northern part of its range and February to April in the south with a gradient between the areas.

The male Xantus's hummingbird sings from within or under a bush, "a quiet, rough, gurgling warble, at times interspersed with rattles...and high, squeaky notes."