Characters.—Black all over, except a frontal band, continuous or interrupted, above the eyes. There is a good deal of variation in this species, more in the female than in the male, the black being in many individuals of a brownish tinge.
Young Males.—Often of a brownish-black, like many of the females.
Female.—With the black generally of a brownish tinge, but often pale or greyish-yellow; sometimes the upper parts are pale yellow and the under parts and side of the head brown, and the area round the nude parts of the face white. (Anderson.)
Distribution.—Lower ranges of Bhutan—its furthest western range—(Pemberton); hill ranges of Upper Assam (Blyth), Sylhet, Chittagong, Aracan.
Habits.—"I first met with this species in Upper Burma," Dr. Anderson relates, "in passing through the magnificent defile of the Irawaddy, below Bhamo, where the river is enclosed by high hills, covered with dense forest, for about fifteen miles of its course. It was early morning, and the air was resonant with the loud cries of this Gibbon; large troops were answering each other from the opposite banks, and the hills echoed and re-echoed the sound. The Hoolock is also common on the Kakhyen hills, on the eastern frontier of Yun-nan; and there, too, my attention was called to them at daybreak, when they passed up from their sheltered sleeping-ground in the deep and warm valleys to heights of about 4,000 feet. We, in the middle distance, first caught a faint murmur of voices, but every minute it became more and more distinct, till at last the whole troop rushed past in a storm of sound, vociferating Whoko! whoko! and in a few more minutes their cry was heard far up the mountain-side. Considering that their progress is almost exclusively arboreal, the rapidity with which they make their ascent is wonderful.
"Associated with this arboreal habit of progression, we find that H. hoolock derives its nourishment from leaves, insects, eggs, and birds, the essential features of sylvan life." It also eats the leaves of Ficus religiosa, the aquatic Convolvulus (Ipomœa reptans), and the brilliant red flowers of the Canna indica. It "has a marked partiality," continues the same naturalist, "for Spiders and their webs, which become tangled in its long slim fingers, and Orthopterous insects are regarded by it with special favour, and over which it utters its peculiar cry of satisfaction. Eggs also are to it a bonne bouche. It was first in the Calcutta gardens that I become aware of the circumstance that small living birds were devoured by it with a method and eagerness which has left no doubt in my mind that this species, in its natural state, must be a scourge to the feathery tribe."
The Hoolock lives in large flocks as a rule, keeping chiefly to the hill forests. Sometimes, however, an old male may be discovered living by himself.
They move chiefly by means of their long arms, by which they swing themselves for prodigious distances from branch to branch, and from tree to tree. They descend hill-sides at a surprising pace, their descent being accomplished by grasping bamboos or branches that bend beneath their weight, and allow them to drop until they can seize the ends of other bamboos or branches lower on the slope and take another mighty swing downwards. They also ascend with great rapidity, swinging themselves from tree to tree. (Blanford.)
When walking on the ground the Hoolock rests on its hind feet alone, with the sole flat on the ground and the great-toe widely separated from the other digits. "They walk erect," writes Dr. Borrough, "and when placed on the floor, or in an open field, balance themselves very prettily by raising their hands over their head and slightly bending the arm at the wrist and elbows, and then run tolerably fast, rocking from side to side; and if urged to greater speed they let fall their hands to the ground and assist themselves forward, rather jumping than running, still keeping the body, however, nearly erect."
VI. THE HAINAN GIBBON. HYLOBATES HAINANUS.