402 BULLETIN 186, UNITED STATES NATIONAL MUSEUM 



down the rock-strewn slopes and where it temporarily followed a 

 more or less level course. The bird flits gracefully from stone to stone, 

 with a sharp, monosyllabic cry, rests for a moment with tail bobbed 

 rapidly up and down, runs this way and that across some wet shelf of 

 rock in pursuit of insect prey, and, finally alarmed, takes off with 

 dipping flight through the low, overhanging branches to vanish 

 around a bend, where the performance is repeated. It is rather less 

 shy than indicus and is much more likely to be seen where the brook 

 is comparatively wide and the rocks are unsheltered by the vegetation 

 of the banks. 



Gyldenstolpe took juveniles at Khun Tan, May 29, and at Doi Pha 

 Sakaeng, July 16 ; I have examples in postjuvenal molt from the coun- 

 try between Ban Choeng Doi and Doi Langka, July 21 and August 

 26. A specimen in postnuptial molt was collected at the base of Doi 

 Mae Kong Ka, October 22. 



Gyldenstolpe notes (1916) that his juveniles had the irides blackish 

 brown ; the bill black ; the feet and toes flesh color. 



The adult has the forehead white, this color continued as a super- 

 cilium above and down behind the eye; the crown, nape, upper and 

 lower back slaty blue-gray; the rump and upper tail coverts white; 

 the wings much as in the preceding species but with the primaries 

 narrowly tipped white (in unworn plumage) and with broad white 

 bases to form a speculum; the tail as in the preceding species; the 

 lores, chin, upper throat, and sides of the head and neck black; the 

 remaining underparts white, the feathers of the breast often with 

 faint, narrow dark tips. The juvenile lacks the white frontal area 

 and has the upper half of the head, nape, and back uniform dark 

 sooty gray; the chin, throat, and breast buffy, the feathers of the 

 last part narrowly edged darker ; the white wing band suffused with 

 buff. 



ENICURUS IMMACULATUS (Hodgson) 



Black-backed Forktail 



[M otacilla (Enicurus)] Immaculatus Hodgson, Asiatick Researches, vol. 19, 1836, 



p. 190 (Nepal). 

 Enicurus immaculatus, Riley, U. S. Nat. Mus. Bull. 172, 1938, p. 402 (Mae Kong 



Ka valley). 



A female collected by Smith at the base of Doi Mae Kong Ka, Janu- 

 ary 19, 1933, and two males and one female taken by me at the same 

 locality, October 18 and 19, 1936, are the only specimens of this fork- 

 tail yet known from Thailand. 



It seems to be restricted throughout its range to feeble elevations 

 but, like others of the genus, requires swift-flowing streams and is 

 not likely to be found away from the broken country at the foot of 

 the mountains. 



