Nyctiphrynus poorwills are small nightjars, with chest feathers that often are fluffed to form an "apron". The sexes are similar in Yucatan Poorwill, but there are two color morphs, a brown morph, which occurs in both sexes, and a rufous morph, which largely is restricted to females. Yucatan Poorwill is cryptically colored, in general nightjar fashion. It has a small white throat patch, and white tips to the outer rectrices, but there is no white in the wings.
Eared Poorwill (Nyctiphrynus mcleodii) also occurs in Mexico, but only on the Pacific slope, so these two species do not overlap geographically. Eared Poorwill also is somewhat paler, with tawnier plumage, and more a distinct collar across the nape. Yucatan Poorwill overlaps geographically with Yucatan Nightjar (Caprimulgus badius), but the nightjar is larger, with longer wings and tail, a rufous collar across the nape, and the male nightjar has more extensive white in the tail than does the poorwill. The song of Yucatan Nightjar also differs from that of Yucatan Poorwill.
The following description is based on Ridgway (1914) and on Cleere (1998):
Adult: Sexes similar. Brown morph: Upperparts generally deep grayish brown, sides of the crown more grayish. The upperparts overall are finely vermiculated with dusky and with more or less medial black streaks; these streaks are broader on the center of the crown and even more so on the scapulars (especially the posterior scapulars). Narrow, indistinct buffy collar on nape. The median wing coverts have small, irregular, terminal white spots. The inner secondaries are light brown, finely vermiculated or sprinkled with dusky and with a very distinct central black stripe; rest of secondaries dusky, crossed by four bands of pale cinnamon spots, these spots more or less broken by dusky vermiculations. Primaries dusky, spotted with cinnamon buff, the tips of the primaries pale brown vermiculated with dusky. Rectrices dull black freckled or mottled with pale grayish buffy, tips of the four outer pairs of rectrices broadly white. Lores, auriculars, chin and upper throat dark sooty brown or brownish black, very finely vermiculated with brown. Lower throat white, forming a conspicuous white patch. "Apron" on breast brownish black, these feathers tipped with grayish vinaceous brown, finely vermiculated with dusky and with a black shaft streak; these brownish tips are smaller anteriorly, but are larger posteriorly. Underparts coarsely vermiculated brown and light grayish, the feathers with a central black streak, and many with a sagittate white terminal spot. Flanks and undertail coverts barred with black and pale dull buffy.
Rufous morph (female only?): Similar to the brown morph, but the overall grayish brown color is replaced with rufescent brown; the black streaks on the crown are narrower; and the white tips to the outer rectrices are slightly narrower.
Little information. Cleere (1968) noted a specimen from early August in molt of the primaries and rectrices, indicative of a complete prebasic molt.
Iris: dark brown
Bill: blackish, brown
Tarsi and toes: brown
Bare parts color data from Ridgway (1914) and Cleere (1998).
Total length: 19.8-20.0 cm (Ridgway 1914), 19.5-22 cm (Cleere 1998), 20.5-21.5 cm (Howell and Webb 1995)
Linear measurements (from Cleere 1998):
male (n not specified, but a minimum of 5)
wing length, range 110-117 mm
tail length, range 101-108 mm
bill length, range 12.7-13.8 mm
tarsus length, range 16.2-17.5 mm
female (n not specified, but a minimum of 5)
wing length, range 109-114 mm
tail length, range 91-108 mm
bill length, range 13.6-14.7 mm
tarsus length, ca 16.0 mm
Mass: male, 21.3 (n = 1; Paynter 1955); female, 27.7 g (n = 1; Russell 1964).