Appearance

Arremonops are sparrows with olive upperparts, a gray head and underparts, dark stripes on the crown and sides of the head, and relatively stout tarsi. Green-backed Sparrow is a typical member of the genus; in this species, the dark stripes on the head are black. Also, Green-backed Sparrow has pale yellow undertail coverts. Males and females are similar. The immature is duller head, and the black crown stripes can be mixed with brown.

Green-backed Sparrow overlaps geographically with Olive Sparrow (Arremonops rufivirgatus), which superficially is similar; but Olive Sparrow has dull brown (not black) stripes on head, duller olive upperparts, and buffier (less yellow) undertail coverts.

The following description is based on Ridgway (1901), and refers to nominate chloronotus; see also Geographic Variation:

Adult: Head slate gray, with broad black or brownish black lateral crown stripes. Back, rump, tail, and wings rather bright olive green. Edge of wing canary yellow. Sides of head slate gray, with a black or brownish black spot before the eye, and a similarly colored long postocular stripe. Chin and throat dull white. Breast and sides grayish, becoming pale olive green on flanks. Belly white; undertail coverts yellowish olive or olive yellowish.

Immature: Similar to adult, but crown dull grayish olive green, and the black stripes can be mixed with brown (Howell and Webb 1995). Underparts mostly grayish, tinged with olive yellowish.

Juvenile: "Entire upper parts dull olive-green (much duller than in adult); crown with stripes indistinct, forming a more or less brownish patch; under parts grayish, but with feather tips and areas along the shaft olive, presenting an indistinctly streaked appearance; flanks and under tail coverts brighter green than remainder of under parts. In comparison with the young [juvenile] of A. conirostris [Black-striped Sparrow], it lacks any yellow on the under parts and possesses only indistinct streaking, lacking the bold, brown streaks of conirostris" (Monroe 1963).

Undescribed in Green-backed Sparrow. Olive Sparrow (Arremonops rufivirgatus) follows a complex basic molt strategy, with an incomplete preformative molt that includes most or all of the body plumage and the secondary coverts, but not the primary coverts, rectrices, or remiges (Pyle 1997, Brush et al. 2013).

Iris: brown

Bill: maxilla black or brownish black; mandible blue gray, the tip sometimes darker but not sharply delineated from the base

Tarsi and toes: flesh

Bare parts color data from Monroe (1963), Howell and Webb (1995) and from specimens in the Museum of Vertebrate Zoology, University of California, Berkeley.

Total length: 15-16 cm (Howell and Webb 1995)

Linear measurements (from Monroe 1963):

male (n = ?), chloronotus

wing length: mean 67.9 mm (range 64.0-72.0 mm)

tail length: mean 58.3 mm (range 54.0-63.0 mm)

bill length (culmen from nostril): mean 9.9 mm (range 8.9-10.9 mm)

tarsus length: mean 23.6 mm (range 20.9-25.2 mm)

female (n = ?), chloronotus

wing length: mean 63.7 mm (range 59.5-67.0 mm)

tail length: mean 55.3 mm (range 51.5-58.5 mm)

bill length (culmen from nostril): mean 9.5 mm (range 8.7-10.5 mm)

tarsus length: mean 23.2 mm (range 22.0-24.6 mm)

Mass:

male, mean 28.1 g (range 25.7-31.2 g, n = 7; Paynter 1955, Russell 1964)

female, mean 25.6 g (range 23.7-29.4 g, n = 4; Paynter 1955, Russell 1964)