Appearance

Oasis Hummingbird is the sole species in the genus Rhodopis. This is a medium sized hummingbird with a very long, slightly decurved bill. Male Oasis Humminbirds also have a long, deeply forked tail; the tail of the female is much shorter, and is only notched. Both sexes are dull green above, with a contrasting cinnamon rump, and are white below with greenish flanks. Males also have a blue to reddish gorget.

The very long, slender bill and the pale cinnamon rump, contrasting with the green back, of Oasis Hummingbird are very distinctive, and this species is unlikely to be confused with any other hummingbird. Purple-collared Woodstar (Myrtis fanny) is significantly smaller; its bill, although slightly curved, is not as long; the female is buffy below, not white; and the male woodstar has a much shorter tail.

The following description is based on Fjeldså and Krabbe (1990), Schuchmann (1999), and Jaramillo (2003) and refers to nominate vesper; see also Geographic Variation:

Adult male: Upperparts olive green; rump and uppertail coverts cinnamon or cinnamon rufous. Small white postocular spot. Tail deeply forked, and the two outer pairs narrower than the inner rectrices, and slightly curved inward; uppersurface of central rectrices grayish olive, remaining rectrices purplish brown. Iridescent gorget rosy violet to purple, becoming turquoise laterally. Underparts whitish to dull white, flanks washed with dull green. Most sources imply that this plumage is retained throughout the year, but Fjeldså and Krabbe (1990) also mention an "eclipse plumage" (basic plumage?), which is similar but in which the throat of the make is "scaled drab brown".

Adult female: Upperparts as in male. Tail much shorter than in the male; only slightly forked, and in fact is slightly double rounded, the third and fourth pairs (counting outwards from the center) slightly longer than the central pairs and the outermost pair. Uppersurface of rectrices olive green or bronzy green; all but the central pair tipped with white, and a broad black subterminal bar. Underparts pale gray, pale buff, or pale grayish buff, darker on the flanks.

Immature male: Similar to adult female, but throat speckled with a few iridescent feathers.

Undescribed.

Iris: dark brown

Bill: black

Toes: black

Bare parts colors data from specimens in the Field Museum of Natural History, Museo de Historia Natural de la Universidad Nacional Mayor de San Marcos, and Museum of Vertebrate Zoology, University of California, Berkeley.

Total length: 11-13 cm (Fjeldså and Krabbe 1990), 13-13.5 cm (Schuchmann 1999); male 12.5–13.5 cm, female 11–11.5 cm (Schulenberg et al. 2010)

Linear measurements:

wing length: 49.3 mm (n = 1; Brown and Bowers 1985)

bill length: 30 mm (Schulenberg et al. 2010); 19 cm, koepckeae (Fjeldså and Krabbe 1990), 22 mm, atacemensis (Fjeldså and Krabbe 1990)

Mass: mean 3.88 g (n = 4, sex?; Brown and Bowers 1985); male, 4.0 g (n = 1; Colwell 2000), female 3.0 g (n = 1; Colwell 2000)