Blue-capped Hummingbird

The Oaxaca hummingbird is 10 to 11 cm (3.9 to 4.3 in) long and weighs 4.1 to 5.4 g (0.14 to 0.19 oz). Both sexes have a straight black bill. Males have a violet-blue forehead, turquoise crown, and emerald green upperparts. Rufous secondaries show as a patch on the folded wing. Their central pair of tail feathers are green and the other four pairs whitish. Their underparts are glittering green with white undertail coverts. Females have green upperparts with a similar wing "patch" as the male's. Their central tail feathers are green and the others white with some dusky green. Their underparts are pale gray.

The Oaxaca hummingbird is found only on the Pacific slope of the Sierra Madre del Sur (also called Sierra de Miahuatlán) in southern Oaxaca. It inhabits the edges and interior of humid montane, semi-deciduous, and pine-oak forest. In elevation it ranges between 700 and 2,600 m (2,300 and 8,500 ft) and is most common below 1,800 m (5,900 ft).

The Oaxaca hummingbird forages for nectar at all levels of the forest from the understory to the canopy. Its diet has not been described in detail but it is known to feed at flowers of Inga, Lobelia, Malvaviscus, and Psittacanthus and some others. It is also assumed to feed on small arthropods like other hummingbirds.