|
June 15, 2010
Proboscis Monkeys - Part 1: A Tree of Their Own
Travelling down the rivers of Borneo, you
may be lucky enough to catch a glimpse of
the unusual and distinct proboscis monkey.
Borneo is home to approximately 44 mammals
species while are endemic to Borneo, one of
which is the proboscis monkey (Nasalis
larvatus), who occupy some of the most
threatened habitat types in Borneo.
Proboscis monkeys are listed as Endangered
and under Appendix I on CITES, restricting
their trade. There are estimated to be less
than 20,000 proboscis monkeys remaining in
Borneo, however, due to their specific
habitat requirements, proboscis monkeys are
effectively restricted to forest strips
along rivers and the interlinking waterways
of swamp forests and coastal mangroves.
Although the total population size for
proboscis monkeys is an estimated 20,000, it
is comprised of many small, isolated
populations.
The most unusual thing you might notice when
you see a proboscis monkey is its nose.
These monkeys are sexually dimorphic --
meaning the males and females look different
-- and one of the main differences is in the
nose.
Adult males have large noses which hang down
over their mouths, and may even extend past
their chin, exceeding 10 cm (4 inches) in
length and reaching up to 17.5 cm (7
inches)! These large noses are used in
sexual displays, as well as amplifiers,
producing loud honking noises. Although
female noses are quite large compared to
other primates, they are considerably
smaller in relation to the nose of the adult
males, and are slightly pointed up.
Adult male and female proboscis monkeys are
also very different in size. Being one of
the largest colobines (leaf eating monkeys),
adult males can reach around 20-24 kg (44-53
lbs). Females, however, are considerably
smaller, reaching around half the weight of
males, weighing approximately 10-12kg (22-24
lbs).
Another feature of proboscis monkeys is
their large bellies, which is a result of
their diet and digestive system. Proboscis
monkeys are highly selective feeders, and
have a specialized chambered stomach
(sacculated) which allows them to eat food
other primates cannot. These chambered
stomachs digest leaves, an easily available
but difficult to digest food source, through
fermentation. However, because their
digestive system is so specialized, it also
means that they are restricted in what they
can eat -- eating foods with high sugar
(such as ripe pulpy fruits) can cause rapid
fermentation and bloat, which is fatal. An
improper diet can also cause the
fore-stomach to become too acidic for the
microflora within it to function properly;
liver and blood disorders; or obstructions
in the intestines or stomach, which also
result in death. This specialized diet is a
major cause of mortality of proboscis
monkeys in zoos, and is a crucial reason why
they are difficult to maintain and should
not be kept in captivity.
Proboscis monkeys live in stable social
groups, the sizes of which can vary from 3
to 26 individuals, and consist of one adult
male, several females and their infants and
juveniles; with groups of males occurring as
well. These groups may also join up with
other groups, and travel together in "bands"
throughout the day.
In the late afternoon, proboscis monkeys
congregate along the waterways to feed,
play, communicate with other groups, and are
where all male groups can check out their
competition and the females in those groups,
before settling in for the night. The
following morning, after feeding, groups
move away from the waterways back into the
forest where they spend their day before
heading back to the water in the afternoon.
As proboscis monkeys live in waterways
throughout the coastal areas of Borneo, with
more than half the population living within
50 km (31 miles) of the coast, they are
adapted to swim. With webbing between their
2nd and 3rd toes, proboscis monkeys are able
to walk on soft mangrove ground, as well as
swim, having been observed to swim fully
submerged for 20 meters (65 feet). Due to
this adaptation, more forest patches are
made available for a proboscis monkey group,
as their movement is not restricted by
water, as it is for most primates. However,
forested areas along water ways are those
that are first habituated by people --
therefore proboscis monkeys are living in
some of the most threatened habitat in
Borneo.
In my next blog, I will talk about some of
the major threats proboscis monkeys are
facing, why they have been labeled as
Endangered, and why local extinctions of
groups are expected to continue unless there
are major changes made in Borneo, and my
consumers all over the world.
|
