Horsfield's Tarsier (Ta rsius
bancanus), also known as the Western Tarsier, is a species of tarsier.
The taxonomy of this species is in doubt, with some subspecies
considered unsure.In fact, over 20 years few studies have been done
on T. bancanus and a taxonomic revision based upon intensive and
systematic field surveys is overdue.These species should be treated as
distinct and named as separate taxa until more definitive evidence is
available.
There are three recognized subspecies of Horfield's Tarsier:
* Tarsius bancanus bancanus
* Belitung Island Tarsier, Tarsius bancanus saltator
* Bornean Tarsier, Tarsius bancanus borneanus
Evolution
There are 3 theories of origin of primates. The first and the oldest
being the arboreal theory which suggests that early primates evolved to
meet the needs of living an arboreal life . They have evolved full
stereoscopic vision to be better able to move through the environment.
The orbits of these early primates underwent orbital convergence to
achieve stereoscopic vision . The reduction of olfaction and the
shortening of the snout occurred corresponding to this increase in
reliance on vision. Also grasping hands and feet with nails instead of
claws were thought to be adaptations to living in an arboreal world.
The visual predation theory puts forward the notion that orbital
convergence, grasping hands and feet, and reduced claws were an
adaptation for nocturnal foraging for fruit and insects on terminal
branches in the shrub layer of the forest. Orbital convergence would
assist in determining the prey's distance without having to move the
head, much like we see in modern day owls.
The last, more recent angiosperm radiation theory stated that the
adaptive radiation primates occurred with the radiation of angiosperms
(flowering plants) that offered new opportunities and an unexplored
niche [13]. The early primates were omnivores that were able to feed on
objects such as fruits, flowers, gums, nectars, and insects that fed
upon these plant parts . The stereoscopic vision evolved to discriminate
between food items at low levels of light and handling them would have
necessitated better hand-eye coordination[15]. Problems with this theory
come from that angiosperms first appeared in the fossil record millions
of years before the first primates and that orbital convergence and the
correlated neurological specializations occurring with are not found in
the early Paleocene primates .
Morphology
The pelage coloration range from pale-olive or reddish brown to pale
or dark grey-brown. The coloration possibly varying with age.Based on 12
collected specimens , the range measurement from head to body is 121-154
mm. T.bancanus have an extremely long tail, which can reach 181 to 224
mm, is hairless except for tufts of hair at the end [18]. This species
has two grooming claws on each foot .The fingers are very long and have
pads on the tips. The toes have flattened nails except for the second
and third toes on hind feet, which bear claw-like nails [19]. It has
large eyes thus do not reflect torchlight. The membranous ears are
slender and almost bare. The molars of this species have high-cusps and
are almost tritubercular . The dental formula of T.bancanus are 2:1:3:3
on the upper jaw and 1:1:3:3 on the lower jaw .
Distributions
T.bancanus are found in Southern Sumatra, Borneo and nearby islands.
Bornean tarsier, T.b. borneanus known from many lowland sites in Sabah,
Brunei, Sarawak and West Kalimantan and above 900m in the Kelabit
uplands in Northern Sarawak. Other records that had been made only from
Kutai and Peleben in East Kalimantan and Tanjung Maruwe in Central
Kalimantan.
Ecology
T.bancanus is a nocturnal species. It sleeps alone during the day in
a tangle of vines or creepers at a height of 3.5 to 5 meters. This
species prefers to sleep, rest, or remain stationary on perches that are
angled 5 degrees from the vertical tree trunks, 1 to 4 cm in diameter
and it sleeps solitarily[26]. Before sunset, T.bancanus will wake up and
waits 10 to 20 minutes then begins moving around the understory and
spend 2 to 1.5 hours of the night foraging for food.T.bancanus can be
found from ground level up at least 7m in the understory.
This species is a carnivorous species. It mainly eats insects by
consuming beetles, grasshoppers, cockroaches, butterflies, moths,
praying mantis, ants, phasmids, and cicadas, but also will eat small
vertebrates such as bats (Chiroptera) which are the horseshoe bat,
Taphozus sp., the lesser short-nosed fruit bat, Cynopterus
brachyotis,and the spotted-winged fruit bat, Balionycteris maculata. and
snakes, of which poisonous snakes have been found to be consumed. For
example the poisonous snake Manticora intestinalis was found to be
hunted for by this species. This species was also found to consume
birds, including: spider-hunters, warblers ,kingfishers,and pittas. It
locates prey primarily by sound and catches the prey with its hands when
foraging.The prey items get killed by bites to the back of the neck and
the eyes are shut when attacking. It will consume the prey start with
the head and work its way down the body.This species drinks by two
different ways, one by drinking from a pool or steam, and two by licking
water from bamboo leaves or from trunks of trees when water is running
down the bark.
T.bancanus is a vertical clinger and leaper hence they known for
their extraordinary leaping abilities by having the elongated tarsus,
the fibula and tibia is fused on the lower third part going towards the
foot. An individual will mainly support itself with its feet and the
tail exerts enough force to hold the individual in place without using
the hands as much because of the pads located on the feet except when
resting the hands are usually placed no higher than nose[38]. The hands
only placed higher up if to maintaining the position of the individual.
Other modes of locomotion of this species are
climbing,quadrupedal,walking,hopping and "cantilevering".
Horsfield's tarsiers are monogamous; by that the frequency of
copulation during estrus is only once per night (Wright et al., 1986a).
Courtship call are performed by the male and he emits 2-3 chirrups while
opening and closing the mouth (Wright et al., 1986a). This call happens
within 5 minutes of looking at the female and the male does during
courtship after the female will perform genital displays to him .If the
female is not in estrus it will emit agonistic call is often followed by
biting and pushing the male away (Wright et al., 1986a). Both of each
call lasts on average for 1 second and the interval between each call is
on average 3 seconds.
Infants are born with their eyes open and fully furred and are able
to groom themselves (Roberts, 1994). The mother will carry her infant in
her mouth and when she forages for food the mother will park the infant
on a branch . Clicks are the call that is uttered by the infant sounds
like "k", "tk", "ki", or a rapid "kooih" and can be
heard when the infant is left alone or is cold . The mother contact with
their infants through this high-pitched calls. Infants were found to
first use the tails as support during resting at 7–10 days . Young
Horsfield's tarsiers leave their range at the onset of puberty, and find
their own territory.
Social grooming in this species only occurs between mothers and
infants which are when one individual grooms another, removing dead skin
and parasites by scratching with their toe claws and licking their fur,
avoiding their faces. Faces are cleaned by rubbing on branches and it is
to reinforce social bonds.
Horsfield's tarsiers mark their territories with scents from urine
and glandular secretions on a substrate while scratching the surface
with its hindlimb toe claws.
Habitat
This species can live in both primary and secondary forests, and it
also lives in forests along the coasts or on the edge of plantations.
Conservation status
The habitat loss rapidly due to forest conversion, oil palm
plantations, fire and logging. Even the species are collected for the
illegal pet trade and wrongly considered a pest to agricultural crops,
and can suffer, directly and indirectly, from contamination from
agricultural pesticides.
Horsefield’s tarsier is listed as Vulnerable in 2008 IUCN Red List of
Threatened Species and protected by law in Indonesia and in Malaysia,
and is listed in CITES Appendix II.
In February 2007, the governments of Brunei, Malaysia, and Indonesia
agreed to protect roughly 220,000 square kilometers (85,000 square
miles) of tropical forest in the so-called "Heart of Borneo".
Environmental group WWF was particularly active in the establishment of
the protected area.In the "Heart of Borneo" project, non governmental
organizations have played role in promoting the critical Heart of Borneo
initiative and in assisting the transboundary nations in its
conceptualization, design, and implementation. The transboundary nations
is to improve biodiversity conservation in Bornean production forests,
and to ensure that such forests are not simply converted to agricultural
land-uses such as oil-palm plantations after logging |
