24 – 31 cm. Polytypic. Relatively large, sexually dimorphic nightjar with rounded wings and tail. Males have a distinctive white collar and have white on the tips of the outer rectrices; the white is replaced by buff in females. There is no white on the wings in either sex. Birds have overall dark barring on body and tail with black spots on wing-coverts.
Cleere (1998) describes similar species that include two monotypic Mexican nightjars (both of which are allopatric to sericocaudatus).
The Yucatan Nightjar (Caprimulgus badius) of the Yucatan Penninsula, Central America, is smaller, paler and has a narrower, more conspicuous, tawny or rufescent collar on its hindneck; the male Yucatan Nightjar also has broader white tips to the three outer tail feathers. Vocalizations of C. badius are similar to the nominate form of C. sericocaudatus.
The Tawny-collared Nightjar (Caprimulgus salvini) of eastern Mexico is also similar but by appearances only. It is smaller and the male has broader white tips to the three outer tail feathers.
C.s. sericocaudaus (descriptions are based on those in Cleere 1998)
Adult male: Forehead, crown and nape are brown, profusely speckled grayish-white, buff and cinnamon, broadly streaked blackish-brown. Very broad, indistinct collar on hindneck tawny-buff barred brown. The mantle, back, rump and uppertail-coverts are brown, lightly barred and speckled cinnamon. The wing-coverts are brown, spotted buff and cinnamon. The scapulars are brown and buff, and boldly spotted blackish-brown, with two small cinnamon spots on feather-tips. The outer primaries are brown, with spotted tawny on outerwebs and barred tawny on innerwebs; inner primaries and all secondaries are brown barred tawny. The tertials are brown mottled grayish-white, buff and cinnamon. The tail is dark brown, faintly and indistinctly barred tawny. The tips of three outermost pairs of rectrices (R5-R3) are white, in band (ca. 20 mm wide), edged buff, extent of white greater on the outer webs; the next pair of rectrices (R2) very narrowly tipped buff; the central pair (R1) densely barred with grayish brown mottling. The lores and ear-coverts are rufous speckled dark brown. The chin and throat are brown with buff barring. There is a large buff patch across lower throat. The breast is brown, spotted with buff and white. The belly and flanks are buff, densely barred brown and heavily spotted white. The undertail-coverts are buff, lightly barred or vermiculated brown. The underwing-coverts are buff, barred and brown.
Adult female: Similar to the male, but is perhaps slightly more brown and paler. The three outermost pairs of rectrices (R5-R3) are narrower (5-10mm) and are tipped buff.
C.s. mengeli (descriptions based on captured adults at CCBS)
Adults (sexes alike): similar to nominate form but contra the description in Cleere (1998) the male has a prominent white collar. The collar of the female is overall buff in color but some of the tips of individual feathers are lighter, sometimes white. Rictal bristles are blackish brown.
Immature: Similar to adults.
Juveniles: Much paler than adults. Crown, scapulars, and wing coverts are grayish brown with distinguishable brown circular markings. The light colored tips on the outer tail feathers are visible in flight.
Chick: covered with golden down; dark brown pin feathers begin to appear by day 3.
Iris dark brown, bill brownish black, darker toward tip; legs and feet blackish-brown.
Measurements are based on a combined data set from literature and from museum specimens from the following museums: Los Angeles County Museum of Natural History; Field Museum of Natural History; Louisiana State University Museum of Natural Science; American Museum of Natural History; Academy of Natural Sciences of Philadelphia; Museum of Vertebrate Zoology, University of California, Berkeley; University of Michigan Museum of Zoology. The data given are expressed as the mean (range; # of individuals measured) with linear measurements in mm and in grams (mass). * = presumably from 1st year adult (Dickerman 1975)
| ||C.s. sericocaudatus ||C.s. mengeli |
| ||male ||female ||male ||female |
| wing || 176 (r=171-185; n=5) || 176.4 (r=166-190.2; n=5) || 158 (r=155-161; n=2) || 161.1 (r=156-166.2; n=2) |
| tail || 145.4 (r=140-148; n=5) || 137.5 (r=130.3-144; n=5) || 128.5 (r=128-129; n=2) || 115.8 (r=115.6-116*; n=2) |
| bill || 10.1 (r=7.5-15.1; n=4) || 10.6 (r=7.8-14.9; n=5) || 8.3 (r=8-8.6; n=2) || 6.2 (n=1) |
| rictal bristle || || 25 (n=1) || || 26 (n=1) |
| tarsus || 15.0 (r = 11.9-18; n=4) || 16.6 (r=14.2-20.9; n=4) || 12.6 (r=11.7-13.5; n=2) || 13.7 (n=1) |
| overall length || 283.2 (r=276.3-287.5; n=3) || 270.7 (r=266.7-276.5; n=4) || 266.8 (r=266.6-267; n=2) || |
| mass || 83 (n=1) || 99 (n=1) || 62 (n=1) || 66 (n=1) |
The following measurements are of live birds which include four adults (two males; two females) captured by Wilkinson at Cocha Cashu Biological Station.
| ||C.s. mengeli|
| wing|| 170 (n=1)|| 171.5 (r=170-173; n=2) |
| tail|| 135.5 (r=135-136; n=2) || 132 (r=129-135; n=2)|
| bill|| 8.7 (r=8.4-9; n=2)|| 9.5 (r=9-10; n=2)|
| rictal bristle|| 26.5 (r=23-30; n=2)|| 29.3 (r=28-30.5; n=2)|
| tarsus|| 19.4 (r=17-21.8; n=2)|| 15.6 (r=14-17.3; n=2)|
| overall length|| || 294 (n=1)|
| mass|| 69.7 (r=69-70.5; n=2)|| 75.2 (r=74.5-76; n=2)|