Roadrunners (Geococcyx) are large, heavy billed, long tailed cuckoos with long, sturdy tarsi. Both species of roadrunner have an erectile crest, and prominent bare skin around the eye. The upperparts of Lesser Roadrunner are dark brown, heavily streaked with white; the underparts are pale buff or buffy whitish, with some dark streaking on the breast. The sexes are similar; juveniles also are similar to adults, but the bare skin around the eye is duller.
Lesser Roadrunner is very distinctive within most of its range, and is unlikely to be confused with any other species. This species overlaps locally in Mexico with Greater Roadrunner (Geococcyx californianus), which is larger with a heavier bill, has whiter underparts, and the throat and breast are heavily striped with blackish.
The following description is based on Ridgway (1916):
Adult: Sexes similar. Crown black, slightly glossed with bronze green and spotted with pale brownish buffy, the spots more numerous on the forecorwn. Lores buffy whitish. Auricular region narrowly and indistinctly streaked with dusky and pale buff or dull buffy whitish. Nape brownish black, the feathers broadly edged with pale brownish buffy. Back and scapulars brown, feathers darker basally and sharply edged with pale buff or buffy white, producing conspicuous streaks. Rump brown, feathers with indistinct paler tips. Uppertail coverts brown glossed with purplish bronze and sharply edged with white. Central pair of rectrices brown glossed with purplish bronze and edged with white; next pair dusky olive glossed with greenish bronze and with a small white terminal spot; remaining rectrices dull black faintly glossed with greenish and tipped with white, the white tip increasing in width successively towards the outer pair. Wing coverts with broad median black streak, becoming brown at the tip, and very broadly tipped with white. Inner secondaries (tertials) brown narrowly bordered with black, broadly and sharply edged with white or white and brownish buff; remaining secondaries dull blackish glossed with bronze greenish, edged with white or buffy white. Primary coverts dull black basally, distal half white. Primaries dull black, with oblique band of white on outer webs of median portion of feathers. Underparts buff, deeper on the flanks; sides of neck and of breast broadly streaked with black. Undertail coverts dusky, sometimes tipped with tawny or rusty brownish.
Juvenile: Similar to adult, but bare facial skin grayish (Howell and Webb 1995); or "above buff tips to feathers, unstreaked, breast with dark spots not streaks, tail feathers narrower than in adult, bare skin around eye blue as in adult" (Payne 2005).
Little information. Selander and Giller (1959) collected a specimen in July in Mexico that was in the early stages of molt. Otherwise all information is from the observations in El Salvador by Dickey and van Rossem (1938). Here a complete basic molt in adults occurs from early August to mid September here also is a partial body molt (prealternate molt?) in February and March, during which some of the rectrices and remiges are replaced. As in many species of cuckoos, the molt of the rectrices "is neither symmetrical nor in sequence". Dickey and van Rossem (1938) also noted overlap of molt and breeding in Lesser Roadrunner in El Salvador.
Iris: dark brown (but silvery white next to the pupil)
Eyelids and postocular region: bright blue to pale, lavender blue; bare skin (usually concealed) on each side of nape scarlet
Bill: maxilla brown, darker on ridge of culmen; mandible gray
Tarsi and toes: gray
Bare parts color date from Dickey and van Rossem (1938).
Total length: 40.5-50.5 cm (Howell and Webb 1995)
Linear measurements (from Ridgway 1916)
male (n = 32)
wing length: mean 144.2 mm (range 136.5-162 mm)
tail length: 278.5 mm (range 231-305 mm)
bill length (exposed culmen): mean 40.5 mm (range 37-45 mm)
tarsus length: mean 50 mm (range 46-54 mm)
female (n = 10)
wing length: mean 142.1 mm (range 138.5-146 mm)
tail length: mean 273.9 mm (range 242-294 mm)
bill length (exposed culmen): mean 39.6 mm (range 37.5-41 mm)
tarsus length: mean 48.9 mm (range 47-50 mm)
Mass (from Payne 2005):
male: mean 186.0 g (range 174-203 g, n = 5)
female: mean 174.0 g (range 162.8-192 g, n = 4)