A large, stocky nighthawk, the Nacunda is sexually dimorphic. The basic appearance is brown, speckled with grayish white and grayish brown, and with a white throat and belly. When in flight the bird appears long-winged with a square or slightly forked tail, and a prominent white band across the bases of the outer primaries. The Nacunda Nighthawk is sexually dimorphic. The white wing band of the male is more well developed; also the male has broad white tips to all but the central pair of tail feathers. The wing band of the female is less developed, and lacks the broad white tips to the rectrices.
Much larger than other neotropical nightjars. Few other species of neotropical nightjar that as extensively white below; Sand-colored Nighthawk (Chordeiles rupestris) is smaller, has more pointed wingtips that lack the white wing band, and has prominent white flashes on the upper surface of the wings.
The following description is based on Cleere (1998), and refers to nominate nacunda:
Adult male: Crown and nape brown, speckled with buff, pale buff and grayish white, heavily spotted with blackish brown; feathers tipped buff. The back, rump, and uppertail coverts are brown, speckled with grayish brown and buff, and spotted with blackish brown. The wing coverts and scapulars are brown, densely speckled with dark brown, buff, grayish buff, and cinnamon, and heavily spotted with blackish brown. The primaries are brown; there is a large white spot almost midway out the feather, on the outermost five (and sometimes six) primaries, with a smaller white on primaries 5-3. The five inner primaries are mottled cinnamon, buff, or grayish white. The secondaries are brown, mottled with grayish white, cinnamon, and buff. The tertials are brown, densely speckled with buff, grayish buff, and cinnamon, and with blackish brown bars. The rectrices are brown, broadly barred with grayish buff and mottled brown. The outermost rectrices (R5-R3) are broadly tipped white (the white tips ca 35 mm in width). Rectrix 2 has a reduced white tip, and is edged with brownish buff. The central pair of rectrices (R1) are grayish brown mottled with brown, and thinly barred with blackish brown. The lores and ear coverts are brown, barred with buff. There is a buff submoustachial stripe. The chin is buff, barred with brown. Throat white, in a large triangular pattern; the lower feathers of the white throat patch are tipped buff. The breast is brown, barred, speckled and spotted with grayish buff and white. The upper belly is white, often thinly barred or vermiculated with brown. Lower belly and the flanks generally white. The undertail coverts are white or buffish white, barred with brown. The underwing coverts are white or buffish white, barred with brown.
Adult female: Similar to the male. The belly, flanks and undertail coverts are white, thinly barred with brown. The white spots on the outer primaries are smaller, and are speckled with brown on the outer webs. The female generally lacks white in the tail, although some females have outermost two pairs of rectrices (R5 and R4) tipped with brownish white, speckled brown; the brownish white tips, if present, may be up to 14 mm wide.
Immature and juvenile: Apparently similar to the adult female.
Chick: Not described.
Data from Belton (1984), Cleere (1998):
Iris: light brown.
Bill: blackish, or brownish with dark tip.
Tarsi and toes: Dark reddish gray, or grayish brown.
Linear measurements are from Cleere (1998); the sample size is not given, but the data are from at least five specimens per sex and subspecies (Cleere 1998: 14):
Wing: nacunda 250-263 mm; minor 223-225 mm
Tail: nacunda 109-123 mm; minor 110-114 mm
Bill: nacunda 14.8-16.4 mm
Tarsus: nacunda 25.1-26.6 mm
Wing: nacunda 230-238 mm; minor 204-234 mm
Tail: nacunda 112-116 mm; minor 91-110 mm
Bill: nacunda 13.5-14.9 mm
Tarsus: nacunda 22.9-25.4 mm
Mass, nacunda: 1 male 188 g, 1 female 170 g (Belton 1984; female (n=?), 161-170 g (Cleere 1998); minor: 1 male 142. g, female (n=4), mean 135 g (range 124-141 g; Haverschmidt and Mees 1994).