The Scrub Nightjar is a small variegated nightjar with cryptic colors and feather patterning. The male has a white throat, and a relatively broad white band across the primaries. The inner webs of the two outer pairs of rectrices are white; little or now white is visible on the closed tail, but when the tail is spread, it shows white longitudinal stripes along the edges. The pattern of the female is similar, but the white band across the primaries is narrower, and there is white only on the outermost pair of rectrices.
The Common Pauraque (Nyctidromus albicollis) has a large geographic range, which includes western Ecuador and Peru. The Common Pauraque is larger, with a longer tail, and has more white in the tail (three, not two, pairs of outer rectrices are largely white) (Cleere 1998, Ridgely and Greenfield 2001b). Scrub Nightjar also may overlap locally in Peru with Band-winged Nightjar (Caprimulgus longirostris decussatus), which has white tips to the outer rectrices, and which also is paler overall.
The plumage of the Scrub Nightjar is very cryptic, colored with browns, buffs, blacks with varying color intensities and patterns that allow for excellent camouflage. The following detailed description is based on Cleere (1998):
Adult male: Upperparts generally grayish brown, speckled with buff and streaked blackish brown. Crown broadly blackish brown. Lores and ear coverts tawny-buff, barred and speckled with dark brown. Broad but indistinct collar on nape, tawny-buff, barred with brown. Wing coverts grayish brown, speckled brown and buff and heavily spotted with buff and pale buff. Scapulars brown, speckled with buff on the inner webs; feathers with large irregularly shaped, blackish brown centers, and broadly edged buff on the outer webs. Primaries brown; primaries 6-10 with a large white spot midway out the feather (this spot often washed with buff on primary 10); a very small white spot on primary 5; remaining primaries irregularly spotted and barred with pale tawny or buff. Secondaries brown, barred and tipped tawny-buff. Rectrices primarily brown. The two outermost pairs are entirely white on the inner webs; the next two pairs are barred indistinctly with pale tawny-buff; the central pair are heavily mottled grayish-brown. The chin and upper throat are tawny-buff, barred and speckled dark brown. There is a white patch across the lower throat, the lower feathers of which are tipped pale buff. Breast grayish-brown, broadly barred buff and pale buff. The belly and flanks are buff or pale buff, indistinctly barred brown. Undertail-coverts buff.
Adult, female: Similar to male, but the white spots on the primaries are smaller, and the white in the tail usually is restricted to the next-to-outermost pair of rectrices (R5).
Immature: The immature can be aged by the somewhat narrow and pointed outer wing and tail feathers and by the pale tips to the outer primaries (Cleere 2006).
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Data from Cleere (1998):
Iris: Dark brown.
Tarsi and toes: Pinkish gray-brown.
The following measurements are based upon an average of at least five specimens personally measured by Cleere and Nurney (1998) and measurements obtained from Schwartz (1968) and Robbins et al. (1994):
Wing (chord): range 132-136 mm (n=5+; Cleere 1998); mean 131.7 ± 3.9 mm (n=10, Robbins et al. 1994)
Tail: range 97-100 mm(n=5+; Cleere 1998); mean 94.9 ± 2.3 mm (n=10, Robbins et al. 1994)
Bill: range 14.6-15.7 mm (n=5+; Cleere 1998)
Tarsus: range 16.8-17.9 mm (n=5+; Cleere 1998)
Wing (chord): range 135-142 mm (n=5+; Cleere 1998), mean 134.1 ± 2.7 mm (n=9; Robbins et al. 1994).
Tail: range 90-101 mm (n=5+; Cleere 1998), mean mean 93.2 ± 4.3 mm (n=9; Robbins et al. 1994).
Bill: range 12.9-14.2 mm (n=5+; Cleere 1998)
Tarsus: range 16.4-18.6 mm (n=5+; Cleere 1998)
Mass, males: range 32.3-39.5 g (n=?; Cleere 1998); mean 35.2 ± 2.9 g (n=10; Robbins et al. 1994)
Mass, females: range 31.0-42.0 g (n=?; Cleere 1998); mean 36.6 ± 3.8 g (n=9; Robbins et al. 1994)