Nightjars are cryptically patterened nocturnal birds, usually in shades of grays and browns. Pygmy Nightjar is a very small, pale nightjar. The upperparts generally are grayish brown, densely speckled with grayish white or with tawny and buff; this species does not have a rufous or tawny nuchal collar. There is a large white patch on the throat, speckled with dusky, and bordered below by a broad cinnamon buff band. The breast is brown, densely spotted and barred with pale buff and with grayish white; the belly and flanks are buff, barred with brown. Males have white tips to the two outer pairs of rectrices. The male also has a white spot on the middle of the four outer primaries, forming a short white band across the open wing; these spots are smaller in the female.
Little Nightjar (Setopagis parvula) is another species of small nightjar that overlaps broadly with Pygmy Nightjar. Little Nightjar differs by having a tawny buff nuchal collar, a broad pale supercilium, andhaving a more contrasting pattern on the wing covers and scapulars. The white wing band of male Little Nightjar is more restricted than in Pygmy, and male Little lacks white in the tail.
Least Nighthawk (Chordeiles pusillus) is typically browner, and has a smaller white throat patch, paler underparts, more pointed wings, and a slightly forked tail. The male Least Nighthawk has a more defined white band across the four outer primaries, which is slightly thinner in females. Least Nighthawk also has a narrow but distinct pale trailing edge to the inner wing.
The following description is based on Cleere (1998), and refers to nominate hirundinaceus; see also Geographic Variation:
Adult male: Forecrown, crown, and nape brown, densely speckled with grayish white and cinnamon. Indistinct thin, white supercilium. Lores and auriculars brown, speckled with grayish white and buff. Back, rump, and uppertail coverts brown, densely speckled with grayish white and cinnamon. Scapulars brown, speckled with grayish white, with a grayish brown or buff spot on the tip of the outer web. Rectrices brown, densely speckled with grayish white, buff, and cinnamon. The outermost rectrix (R5) has a white spot (ca 15 mm across) at the tip of the inner web; the next rectrix (R4) has a broader (15-18 mm) white tip across both webs; the two inner pairs (R3-R2) indistinctly barred with grayish white; and the central pair (R1) broadly barred with grayish white mottling. Wing coverts brown, densely speckled with grayish white, buff, and cinnamon, and spotted with grayish white, grayish brown, and buff. Primaries brown; white spot, about half way out the length of the feather, on the inner web of the outermost primary (P10), on the inner or on both webs of P9, and across both webs of P8-P7. Innermost primaries (P1-P4) narrowly tipped with dirty buff. Secondaries brown, barred with buff on the inner webs. Tertials brown, densely speckled with grayish white, buff, and cinnamon. Narrow lateral throat stripe buffish. Chin and upper throat white, barred with brown. Throat with a triangular white patch, merging into a broad cinnamon buff band, spotted with brown, on upper breast. Breast brown, spotted and barred with pale buff and grayish white. Belly and flanks buff barred with brown. Undertail coverts buff, lightly barred with brown. Underwing coverts buff, barred with brown.
Adult female: Similar to adult male, but slightly paler. Smaller spots on the four outer primaries. Tail lacks white, and is speckled and barred tawny buff.
Immature: Paler than adult. Often heavily tinged with cinnamon. Broad buffish tips on the primaries.
Juvenile: not described.
Little information. The primaries are molted in a descending fashion, from the innermost out. Specimens with primary molt collected in March (cearae), late June, late November, and early December (Cleere 1998). Tail molt noted in museum specimens collected in late June and November (Cleere 1998).
Iris: dark brown
Bill: blackish brown
Tarsi and toes: blackish brown
Bare parts color data from Cleere (1998).
Total length: 16-20 cm (Cleere 1998), 18 cm (van Perlo 2009)
Linear measurements (from Cleere 1998):
wing length: male, range 119-130 mm; female, range 121-129 mm
tail length: male, range 77-94 mm; female, range 88-93 mm
bill length: male, ca 11 mm; female, ca 12 mm
tarsus length: male, 16.5 mm (n = 1); female, 15.6 mm (n = 1)
Mass: male, 32 g (n = 1; Mazar Barnett et al. 2014)