(520) Enicurus immaculatus.
The Black-backed Forktail.
Enicurus immaculatus Hodgs, As. Res., xix, p. 190 (1836) (Nepal). Henicurus immaculatus. Blanf. & Oates, ii, p. 85.
Vernacular names. Inruidiba gajeba (Kacha Naga).
Description. Forehead, short supercilium and round the back of the eye white ; rest of head, chin, throat, back and wing-coverts black; rump and upper tail-coverts white; tail black with broad white bases and tips, the two outer pairs pure white; tips of greater coverts and bases of quills white forming a broad wing-bar; tips of secondaries white, broadly so on the innermost; below from lower throat to under tail-coverts white.
In many specimens the head and upper back have a faint slaty tinge, but this appears to be purely individual and in no way a geographical variation.
Colours of soft parts. Iris dark brown; bill black; legs and feet white, fleshy white or yellowish white.
Measurements. Wing 85 to 94 mm.; tail 100 to 118 mm.; tarsus 26 to 27 mm.; culmen 16 mm.
Distribution. Sub-Himalayas from Garhwal to Assam, Chin Hills, Burma South to the Malay Peninsula.
Nidification. Similar to that of the Slaty-backed Forktail. It breeds at low elevations in April and May, making a nest quite typical of the genus but generally laying only three eggs. These vary much but are typically pale and rather sparsely marked with bright pale reddish brown. 1 have one clutch with a pale green ground and another which is densely marked all over with small specks of dark reddish brown. Twenty-five eggs average 20.8x15.8 mm.: maxima 21.6x16.0 and 21.2x16.3 mm.; minima 20.0 X15.5 and 20.3 x 15.1 mm.
Habits. Those of the genus. In Assam we found them principally on the larger hill-streams close to the Plains, but where the current was still rapid. They remain below 2,500 feet and are more common below 1,000 feet than above that level.