Horsfield's tarsier (Cephalopachus bancanus) is the only species of tarsier in the genus Cephalopachus. Named by American naturalist Thomas Horsfield, it is also referred to as western tarsier. The species occurs on Borneo, Sumatra and nearby islands and is, like other members of the group, entirely nocturnal.
Taxonomy
Although Horsfield's tarsier was usually placed in the genus Tarsius with all other living tarsiers, it is quite distinct from the Philippine tarsier and the various tarsiers of Sulawesi and nearby islands; therefore, scientists have placed it in a separate genus, Cephalopachus.
The taxonomy of this species is in doubt, with some subspecies considered unsure. In fact, over 20 years few studies have been done on C. bancanus and a taxonomic revision based upon intensive and systematic field surveys is overdue. The IUCN believes that these subspecies should be treated as distinct and named as separate taxa until more definitive evidence is available. When splitting the species into its own genus, Colin Groves and Myron Shekelle recognized the natunensis population as a distinct subspecies. the head to body measurement range from . Horsfield's tarsier has an extremely long tail which can reach and is hairless except for tufts of hair at the end. 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. The dental formula of Horsfield's tarsier is 2:1:3:3 on the upper jaw and 1:1:3:3 on the lower jaw.
Biology
Horsfield's tarsiers are nocturnal, sleeping alone during the day in a tangle of vines or lianas at a height of . This species prefers to sleep, rest, or remain stationary on perches that are angled 5 degrees from the vertical tree trunks, in diameter, and it sleeps solitarily. Before sunset, Horsfield's tarsier will wake up and wait 10 to 20 minutes before moving around the understory and spending 1.5 to 2 hours of the night foraging for food. Horsfield's tarsier can be found from ground level up to a height of or more in the understory. but also will eat small vertebrates such as flying frogs, It will consume the prey starting with the head and working its way down the body. Horsfield's tarsier is a host of the acanthocephalan intestinal parasite Moniliformis tarsii.
Like all tarsiers, Horsfield's tarsiers are vertical clingers and leapers, known for extraordinary leaping abilities. An individual will mainly support itself with its feet and the tail, both exerting enough force to hold the individual in place. The hands are not always used because of the pads located on the feet provide adequate grip. The hands are usually placed no higher than its nose except when resting; the hands are only placed higher up to maintain the position of the individual. If the female is not in estrus, she will emit an agonistic call which is often followed by biting and pushing the male away. The mother will carry her infant in her mouth and when she forages for food the mother will park the infant on a branch. Infant sounds are mostly clicks: "k", "tk", "ki", or a rapid "kooih" and can be heard when the infant is left alone or is cold. 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. Additionally, the species is also collected for the illegal pet trade and wrongly considered a pest to agricultural crops. It can suffer, directly and indirectly, from the use of agricultural pesticides.
Horsfield's tarsier is listed as vulnerable in the 2008 IUCN Red List of Threatened Species, In the "Heart of Borneo" project, non-governmental organizations (NGOs) have played a role in promoting the critical initiative and in assisting the neighboring nations in its conceptualization, design, and implementation. The countries are 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.
Gallery
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File:Tarsier - Tarsius tarsius - NHMI.jpg|Cephalopachus bancanus bancanus from Bangka in National Museum of Ireland, Dublin
File:Tarsius di Belitung 06.jpg|Cephalopachus bancanus saltator from Belitung
File:Bornean Tarsier (Cephalopachus bancanus borneanus) (8067063777).jpg|Cephalopachus bancanus borneanus
File:Stamp of Indonesia - 2010 - Colnect 248262 - Belitung Island Tarsier Tarsius bancanus saltator.jpeg|Postage stamp
File:Sofyan Efendi Tarsius Mencari Mangsa DSC 0837.jpg
File:Stamp of Sarawak - 1950 - Colnect 306198 - Western Tarsier Cephalopachus bancanus.jpeg|Postage stamp featuring the western tarsier and George VI (top left)
File:Tarsius Fransiskus Simbolon.jpg
File:Cephalopachus bancanus borneanus 49161649.jpg|In darkness
</gallery>