Travel Reference
In-Depth Information
We hired a fl at-bottomed boat to take us up the Sekonyer River, to visit the
Canadian primatologist Birute Galdikas at her orangutan research station.
On the way we surprised a troop of proboscis monkeys in a tree overhanging
the river. The troop we encountered was a collection of several male-dom-
inated harems. Surplus males who do not have harems band together into
separate (and presumably frustrated) single-sex troops.
These monkeys, even the babies, have swollen stomachs, signs that they
are foregut fermenters like the hoatzins. The faces of the female and imma-
ture proboscis monkeys resemble those of their close relatives the langurs,
but the males have enormous fl eshy red noses that droop down over their
mouths and that swell when they are angry. When this happens they look
like bad-tempered, overweight comedians. As they scream at observers they
sometimes pile on another level of threat by displaying bright red erections.
Proboscis monkeys, like many primates, are endangered by habitat loss.
They are now found only in the lowland river systems of Borneo, though they
were almost certainly more widely distributed in the past. Like the hoatzins
these animals are ecological specialists. At the extreme, evolution can some-
times lead to adaptations so precise that they cut of any avenues of escape
if the environment changes. This seems to have happened to the proboscis
monkeys. They cannot even be raised in zoos, because they soon waste away
and die in captivity.
Two thirds of the diet of proboscis monkeys consists of leaves. They
spend most of their time in coastal mangrove forests, where leaves of man-
grove and pedada trees are plentiful. Some of them do spend part of their
time in the rich and diverse forests that lie just inland of the mangroves,
where many dif erent kinds of fruit are plentiful. But they tend to eat only
unripe fruits, ignoring the ripe and sugary fruit that abound in the forest.
The bitter, tannin-rich mangrove leaves are their chief source of food, except
during seasons when fruit is plentiful.
7
Why do these monkeys confi ne themselves to such a monotonous and—
at least to an omnivorous primate like myself—apparently unappealing diet,
Figure 27
(
opposite
) This male proboscis monkey,
Nasalis larvatus
, is on the Kinabatangan
River in Sabah, Borneo. Notice his fermentation-swollen stomach.
