(_Hylobates lar_)
The name gibbon, which is of unknown origin, and appears to have
been first used by the French naturalist Buffon, is applied to the
members of the smallest representatives of the man-like apes, all of
which differ from their larger cousins, the chimpanzi, gorilla, and
orang-utan, by retaining small bare patches on the buttocks. In this
respect they show evidence of kinship to ordinary monkeys and baboons,
in which, however, these naked callosities, as they are called by
naturalists, attain much greater development.
Gibbons agree with the larger man-like apes in the complete absence
of the tail, but are distinguished by the great length of the limbs,
more especially the front pair, so that when these curious pigmies
are standing upright on their feet, their hands touch the ground.
It is very interesting to note in this connection that gibbons are
the only man-like apes which habitually assume the erect posture in
walking, when the arms are usually elevated and in some cases extended
horizontally, thus giving a most remarkable appearance to their owners.
All the members of the group are confined to tropical south-eastern
Asia, where they range from the eastern portion of the Himalaya
through Burma and the Malay countries to the island of Hainan,
off the southern coast of China. The largest species, the siaman
(_Hylobates syndactylus_) of Borneo, does not much exceed one yard
in height. In colour they are very generally black, often, as in the
species represented in the Plate, with a narrow white band or fillet
surrounding the greater part of the face, or making merely a line
above the eyebrows. In the white-handed species, forming the subject
of the illustration, the white fillet attains its fullest development,
and the hands and feet are likewise white. This species inhabits the
mountain-forests of Tenasserim at elevations between three thousand and
five thousand feet, whence it extends through the Malay Peninsula. Its
near relative the hulok (_H. hulok_), whose range extends from Assam to
Arakan and the neighbouring districts, lacks the white hands and feet,
while the fillet on the face merely forms a band over the eyebrow. In
the Hainan gibbon (_H. hainanus_) even the eyebrow-band is wanting.
A specimen of this last-named species, which is very near akin to
the hulok, afforded a surprise to naturalists in that it changed the
colour of its coat during its sojourn in the London Zoological Gardens.
When obtained in 1897, at an age of about six months, its colour was
dark smoky grey, but this soon changed to black, which persisted till
after the animal’s arrival in London in January 1904. In February
of that year the fur began to assume a greyish tinge; and by autumn
the entire coat had become silvery, or stone, grey, except for a
black stripe down the middle line of the head. It does not, however,
appear that this colour-change is universal in the species; for another
captive specimen believed to be about a dozen years old was wholly
black.
[Illustration]
This is confirmed by the observations of a French traveller in the case
of the white-cheeked gibbon (_H. leucogenys_) of Annam and Siam, in
which two distinct colour-phases are noticeable.
These gibbons commonly go about in parties of six or seven; and while
some individuals are black with white whiskers and a band on the sides
and lower part of the face, in others the general colour is golden
yellow with no white on the face. That the two phases are specifically
identical is certain, and it does not appear that the light-coloured
individuals eventually become dark, or _vice versa_. The natives, it is
true, have an idea that the light-coloured individuals are the females,
but this seems to be disproved by the fact that they are much less
numerous than the black ones; and it thus appears probable that the
species exhibits two distinct colour-phases.
Gibbons are almost wholly arboreal apes; and in the trees they move
about mainly with the aid of their long arms, by means of which
they swing themselves from bough to bough, and thus from one tree
to another, so that a whole troop will traverse the forest without
descending to the ground. So active and agile indeed are these apes,
that when confined in open cages they will catch birds on the wing,
which apparently form part of their food. In addition to these, gibbons
subsist on fruits of various kinds, leaves, young shoots, insects, and
spiders.
All gibbons have a remarkably powerful double-note cry, like _hu-lok_,
which has a wailing sound, and awakes the echoes in the early morning
and again at evening in the forests inhabited by these apes. At a
distance the cry has some faint resemblance to the human voice; but at
close quarters it is enough to drive the traveller, when resting in his
tent, well-nigh distracted.