I first met with this species in Upper Burma, in passing through the magnificent
defile of the Irawady, below Bham6, where the river is enclosed by high hills,
covered with dense forest, for about fifteen miles of its course. I t was early morning
and the air was resonant with the loud calls of this Gibbon; large troops were
answering each other from the opposite banks, and the bills echoed and re-echoed
the sound. The Hoolock is also common on the Kakhyen hills, on the eastern
frontier of Yunnan; 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 a t 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 th a t H. hoolock
derives its nourishment from leaves, insects, eggs and birds, the essential features
of sylvan life. From a series of observations made in the Zoological Gardens,
Calcutta, on the food of this species, we learn that it eats, with evident satisfaction,
the leaves of the following trees : Mormga pterygosperma, Gaertn., Spondias mcmgi-
fe ra , Pers., and Ficus religiosa, Linn. Like the leaf-eating monkeys, suoh as Senrno-
pitheous entell/us, it devours with avidity the leaves of Beta, vulgaris, Mog., and
those of the aquatic convolvulus, I . repta/ns, Poir. With the Ourang-outän it also
manifests a decided predilection for the bright-coloured flowers of Ga/nna mdica,
Linn.
I t is no new fact th a t JET. hoolock, like its congener H . lar, has a marked partiality
for spiders and their webs, which become tangled in its long slim fingers, and
th a t orthopterous insects are regarded by it with special favour, over Which it utters
its peculiar cry of satisfaction. Eggs also are to it a bonne bouche. I t was first in
the Calcutta gardens tha t I became 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 th a t this species, in its natural state, must be a scourge to the feathery
tribe. The living bird being seized by the body, the work of destruction is begun
at the head. The hoolock in so doing forcibly reminded me of the course pursued by
th a t nocturnal nest-harrier Nycticebus tardigradus.
As is well known, this species has the most westerly distribution of the members
of the genus. Pemberton,1 who was an accurate observer, records th a t it
occurs in the lower ranges of Bhutan; and a remark of Hodgson’s® would seem to
favour the supposition th a t it occasionally finds its way even to the sheltered valleys
of Nepal, as he mentions th a t his collectors were alarmed in the Kachar3 by the
1-Journ. As. Soc. Beng. vol. viii. 1839, p. 272. i L . c., 1832, p. 339, foot-note,
3 L . c., p. 339. Hodgson applied the name Kachar to the northern region of Nepal.
HYLOBATES. 3
apparition of a wild man, from which, instead of shooting it, they fled away. This
animal, they said, moved erectly, and was covered with long dark hair, and had no
tail. Blyth1 also observes that it exists in the hill ranges to the eastward of Upper
Assam, in the region inhabited by the JNagas and Ahors, where it abounds in the
upland forests in parties of from 100 to 150 individuals. From thence it ranges in
a south-westerly direction through the hill region of Assam to Sylhet and Kachar,
and the Khasia and Garo hills, in the last of which it is prevalent;® it is also
apparently found in some parts of Mymensing. I t spreads through the mountains
to the north and east of Chittagong, through Arracan, and is distributed southwards
as far as Martaban. From Assam and Munipore it crosses the valley of the
Irawady, and penetrates into the range of mountains tha t define its eastern lim it;
but it does not pass into the high, but treeless, country to the east of Nantin.
Swinhoe3 mentions a species of Black Gibbon said to exist in the country to the
west of Canton, and suggests th a t it may be the same as the a r iim a .1 found in
Hainan, and which he had attempted to identify with H. pileatus *
In Arracan and M artaban i t is associated with H . lar; the latter, however, does
not appear to extend into the northern portion of the Irawady valley.5
The variation of colour, which is so observable in this species throughout the
area of its range, seems to be more distinctive of the female than of the male sex,
as it would appear to be a rare circumstance to find an adult male otherwise tbpn
deep black, whereas females of mature age are not unfrequently pale yellow.
At the same time it is a well-ascertained fact th a t young males occasionally present
a similar variation, but whether they become black as they grow older has not been
determined. Even in females adhering most to the characteristic hue of the
species, the black is always of a less deep tin t than in the adult male, and they
generally have a brownish tinge.
I have observed females from Assam and Cachar in which the upper parts were
pale yellow and the under parts and the sides of the head brown, whilst the area
immediately surrounding the nude parts of the face was so white as to contrast
with the surrounding yellow. This type of coloration approaches that of the
“ Ungka puti ” or H. agilis. In other females from the same region, the fur instead
of being pure yellow is greyish yellow, and their resemblance to H. leuciscus
is such that I have seen hoolocks of this type referred to tha t species by able
zoologists.
Black would seem to be the prevailing colour of the young at birth, but the
not unfrequent occurrence of bright yellow individuals in a species the adults of
1 Journ. As. Soo. Beng. 1844, p. 464.
2 l i p tyP0 was probably obtained from these hills, as Dr. Harlan’s specimen came from Goalpara.
8 Proe. Zool. Soc. Lond. 1870, p. 615.
4 I b id , p. 225. Du Halde (Descrip. Emp. Chin. vol. 1, p. 1181, in his description of the kingdom of Mansi, men-
tions a great black ape.
5 Tiokell states that S . la r extends to the northern confines of Pegu, and limits its westerly distribution to the
east of the spur dividing British Burma from Arracan' (Journ. As. Soc. Beng. 1864, p. 196).