Tarsius bancanus
western tarsier

Tarsius bancanus is found in the Melay archipelago, on the islands of Sumatra and Borneo, as well as on several smaller islands. It can also be found on southern Sumatra, but its range is thought to be restricted in the north by teh Musi River. ("Tarsiidae (Tarsiers)", 2003; Niemitz, 1984; Shekelle and Yustian, 2010)

Preferred habitat of Tarsius bancanus is primary and secondary forest, although it can also be found in mangroves and forest edges. It is a vertical clinger and leaper, and generally does not venture into more open areas unless both prey and small-diameter trees to cling to are present. It can also be found along the forest edge and in fruit plantations. Although it is generally described as a lowland species, residing below 100 m in elevation, sightings above 1200 m have been documented. ("Tarsiidae (Tarsiers)", 2003; Niemitz, 1984)

The most striking feature of tarsiers is their large eyes, which are larger than those of any other mammal, with respect to body size. Tarsius bancanus is small. Males are 12 cm in length on average and range in mass from 122 to 134 g. This species is sexually dimorphic, as females are on average 10 grams lighter than males. Its fur is grey and/or brown and does not help distinguish it from the other tarsiers species. It has a very long tail, nearly twice as long as its head and body. The tale is scaly in appearance, with the exception of a tuft of hair near the distal end. In general, tarsiers have extraordinarily long hind legs (the longest legs of any mammal in proportion to body length), which contributes to their primary mode of locomotion as vertical clingers and leapers. The forelimbs are rather shorter. All four limbs end in long, thin digits, and the front digits have disc-like pads. (Crompton and Andau, 1986a; Niemitz, 1984)

It was previously assumed that tarsiers, including Tarsius bancanus, had a high incidence of monogamy. However, recent evidence suggests that the mating system is highly dependent on prey availability, and that T.bancanus is most likely polygynous. Females signal their readiness to mate both chemically and visually. When in estrus, females exhibit labial swelling and scent-rubbing near territorial borders shared with males. Once males identify estrous females, the often perform "courtship calls." (Niemitz, 1984; Roberts, 1994; Simons, 1986)

Tarsius bancanus mates non-seasonally, and gestation lasts 178 days on average. It has 1 offspring per mating period, which can be up to 25% of the mother body weight. This species generally has slightly more than one birth per year, with an average inter-birth timespan of 258 days. Tarsius bancanus are moderately precocial at birth, as they are able to climb but not leap. Most young are weaned by 80 days after parturition. (Roberts, 1994; Simons, 1986)

After parturition, male western tarsiers are aggressively chased away by the mother until the baby reaches maturity. Captive males have been known to kill their young. Young do not develop locomotor independence for about four weeks; until then, they are "parked" while mothers forage for prey. Unlike many other primates, mother's rarely carry young, which may be due to the large-size of newborns. Other than providing milk and protection from the father, mothers offer limited care to their offspring. (Niemitz, 1984; Roberts, 1994)

Little is known about tarsiers' lifespan, but is estimated for T. bancanus at 12 years. The relative lack of predators and limited fecundity of tarsiers points to a relatively long lifespan. ("Tarsiidae (Tarsiers)", 2003; Roberts, 1994)

Tarsius bancanus is a vertical clinger and leaper. It uses its tail and hind limbs to support itself on vertical surfaces, normally saplings. They strongly prefer trees with trunks smaller than 4 cm in diameter, with the majority being about 2 cm. Its upper vertebrae are modified to allow the head to rotate 180 degrees. Leaping makes up the majority of its locomotion, and it spends only 5% of its time on the ground. Tarsius bancanus is able to leap horizontal distances up to 45 times its body length, or about 5.8 meters. It is completely carnivorous and often captures prey by leaping. It prefers prey that are on tree trunks rather than on the ground, where it is less mobile. Regardless of where its prey is caught, T. bancanus returns to a tree to perch to consume its prey. ("Tarsiidae (Tarsiers)", 2003; Crompton and Andau, 1986a; Crompton and Andau, 1986b; Niemitz, 1984; Roberts and Kohn, 1993)

Western tarsiers are nocturnal and sometimes crepuscular and are most active in the hours immediately after dusk. The tarsier's gigantic eyes allow it to hunt at night. Differing from other tarsiers, the western tarsier is quite solitary, coming in contact with other members of its species only for mating, establishing territory, or raising young. Western tarsiers often return to the same general area to sleep, if not to the same perch. They tend to hunt within 1 m of the ground, and sleeping perches are usually found on a vertical or near-vertical structure over 4 m high. ("Tarsiidae (Tarsiers)", 2003; Crompton and Andau, 1986a; Crompton and Andau, 1986b; Niemitz, 1984; Roberts and Kohn, 1993)

The home range of western tarsiers ranges from 0.045 km^2 to 0.113 km^2, with an average of 0.085 km^2, and male territories tend to be slightly larger than those of females. Radio-telemetry data of western tarsiers showed that males traveled farther during the night than females. ("Tarsiidae (Tarsiers)", 2003; Crompton and Andau, 1986a; Crompton and Andau, 1986b)

Tarsius bancanus relies mostly on sight for foraging and depends upon sound and smell for intraspecific communication. Of all tarsier species, T. bancanus is the least communicative. Where touching and grooming are common in most other species, it has only been documented between mothers with young and mating pairs. Territory is marked with urine, scent from glands in the ano-genital region, and secretions from the epigastric gland. Tarsius bancanus communicates with potential mates via squeaks and whistles, and physical contact prior to copulation is usually initiated by grasping the tail. (Niemitz, 1984)

Western Tarsiers are exclusively carnivorous, most commonly feeding on insects. They consume almost any kind of insect, as well as some small vertebrates, including birds, mammals and reptiles. The prey upon anything that moves, including animals as large as themselves. They have even been sighted preying upon spotted-winged fruit bats tangled in mist nets. ("Tarsiidae (Tarsiers)", 2003; Hodgkison and Kunz, 2006; Jablonski, 1994; Niemitz, 1984; Roberts and Kohn, 1993; Rosenberger, 2010)

There is little information available on the major predators of western tarsiers. Their brown/grey pelage allows them a certain degree of camouflage and helps decrease risk of predation. More importantly, their arboreal nature keeps them out of reach of most predators, however, snakes and arboreal mammals (e.g., slow lorises) are likely their primary predators. They are likely most vulnerable when they are chewing, as they are unable to hear approaching predators. ("Tarsiidae (Tarsiers)", 2003; Niemitz, 1984)

Western tarsier are primarily insectivorous, and may help control insect pest populations. In addition, they are host to various species of intestinal worm (Moniliformes tarsii and Moniliformes echinosorexi), tapeworms and roundworms. Little else is known of parasites specific to this species. ("Tarsiidae (Tarsiers)", 2003; Deveaux, et al., 1988; Niemitz, 1984; Roberts, 1994)

Although Tarsius bancanus may help control insect pest populations throughout its range, there are no known positive effects of this species on humans

There are no known adverse effects of Tarsius bancanus on humans.

Tarsius bancanus is classified as "vulnerable" on the IUCN's Red List of Threatened Species, primarily due to a 30% habitat loss over the last 20 years. Despite this, more information is needed to determine overall population trends. Major threats include habitat loss due to forest conversion to palm plantations and collection of individuals for the illegal pet trade. Despite the fact that this species is 100% carnivorous, it is sometimes considered an agricultural pest and appears to be especially vulnerable to contamination from agricultural pesticides. This species is listed under Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and is protected by law in Indonesia and Malaysia. ("Tarsiidae (Tarsiers)", 2003; Shekelle and Yustian, 2010)