Nightjars are cryptically patterned nocturnal birds, with plumage that usually is dominated by shades of grays and browns. Nightjars also have short bills with a very broad gape, and very short tarsi. Blackish Nightjar is a small, dark, short tailed nightjar. The plumage generally is blackish, but is densely marked with small whitish, grayish, and buff spots. There also is a narrow white band on each side of the lower part of the throat. Males have a small white spot on three of the outermost primaries, forming a small band on the spread wing, and narrow white tips to outer rectrices; females, however, lack white on the wings and tail.
Blackish Nightjar is distinguishable, across most of its range, by its small size and very dark plumage. Locally, however, it overlaps with other nightjars that are somewhat similar in appearance. Blackish Nightjar is particularly similar to Roraiman Nightjar (Setopagis whitelyi), which is restricted to tepuis of southeastern Venezuela and adjacent Guyana and northern Brazil. Where these two species overlap, however, Roraiman Nightjar, occurs at higher elevations (1300-1800 m) and so these twp nightjars are not syntopic. Roraiman Nightjar also is slightly larger and even blacker. The male also has prominent white spotting on the wing coverts, and a larger white wing band than does male Blackish. Females of the two species are more similar, however.
Another nightjar of the tepuis, subspecies roraimae of Band-winged Nightjar (Systellura longirostris), also has dark plumage and is similar to Blackish Nightjar. As with Roraiman Nightjar, however, Band-winged Nightjar is restricted to higher elevations (1300-2300 m) and so rarely if ever is syntopic with Blackish Nightjar of the lowlands. Band-winged Nightjar is larger than Blackish, and both sexes of Band-winged Nightjar have a rufous or tawny nuchal collar, lacking in Blackish. Male Band-winged also can be distinguished by the larger white wing bands and larger white tips to the outer rectrices.
Cayenne Nightjar (Setopagis maculosa) is only known from a single specimen (male) from French Guiana. Cayenne Nightjar is browner and more variegated and wings are more pointed, with more white, than those of Blackish Nightjar.
The following description is based on Cleere (1998):
Adult male: Upperparts generally (forecrown to uppertail coverts) blackish brown, spotted with tawny, grayish white, and cinnamon. Rectrices dark brown, the three outer pairs (R3-R5) indistinctly and faintly barred with pale buff; the two inner pairs (R1-R2) indistinctly barred with grayish brown and buffish mottling. The tips of R3-R4 (and occasionally R2) with narrow (ca 1 cm) white band; R5 also tipped with white, but only on the inner web. Scapulars blackish brown spotted with tawny, and broadly edged with buff on the outer webs. Wing coverts blackish brown, spotted with tawny, grayish white, buff, and cinnamon. Primaries dark brown; small white spot, at about the midlength of the feather, on edge of the inner web of the next to outermost primary (P9); on inner web or both webs of P8; and on both webs of P7; the inner webs of the inner primaries barred with buffish along the edges. Secondaries dark brown, barred buffish along edges of inner webs. Tertials blackish brown, flecked and spotted with grayish white. Lores and auriculars blackish brown, barred and spotted with buff and cinnamon. Chin and upper throat blackish brown. Lower throat white, or with a small white patch on either side of lower throat. Breast dark brown, barred buffish white, buff, and tawny. Belly and flanks buffish, barred with brown, grayish buff, and pale cinnamon. Undertail coverts buff.
Adult female: Similar to adult male, but lacks the white markings on the wing and tail.
Immature and juvenile: Similar to adults but usually slightly paler.
Chick: Covered in grayish down at hatching.
Immature and juveniles: similar to adults but usually slightly paler.
Little information. Adults possibly undergo a complete post-breeding molt. Complete molt noted in February in Venezuela (Willard et al. 1991). Primaries are molted descendantly, from innermost out (Cleere 1998).
Iris: brown, dark brown
Bill: black, blackish
Tarsi and toes: black, dark brown
Bare parts color data from Willard et al. (1991) and Cleere (1998).
Total length: 19.5-21 cm (Ridgely and Greenfield 2001b), 19.5-21.5 cm (Cleere 1998), 20 cm (Hilty and Brown 1986), 21 cm (Hilty 2003)
Linear measurements (from Cleere 1998):
male (n = ?)
wing length: range 139-152 mm
tail length: range 88-104 mm
bill length: range 13.2-13.9 mm
tarsus length: range 15.9-17.0 mm
female (n = ?)
wing length: range 134-154 mm
tail length: range 87-103 mm
bill length: range 11.0-13.6 mm
tarsus length: range 15.0-17.0 mm
Mass: male, mean 35.9 g ± 2.0 g (range 32.5-39.0 g, n = 7; Willard et al. 1991); female, mean 35.4 g ± 2.6 g (range 32.0-39.0 g, n = 5; Willard et al. 1991)