Horsfield’s tarsier (Tarsius bancanus)

Also known as: Western tarsier
Synonyms: Tarsius natunensis
  
French: Tarsier De Bornéo
KingdomAnimalia
PhylumChordata
ClassMammalia
OrderPrimates
FamilyTarsiidae
GenusTarsius (1)
SizeHead-body length: 11.5 - 14.5 cm (2)
Tail length: 20 - 23.5 cm (2)
Female weight: 107 - 127 g (2)
Male weight: 122 - 134 g (2)

Horsfield's tarsier is classified as Vulnerable (VU) on the IUCN Red List (1) and listed on Appendix II of CITES (3).

Subspecies: Horsfield’s tarsier (Tarsius banacus bancanus) is classified as Endangered (EN), the Bornean tarsier (Tarsius banacus borneanus) is classified as Vulnerable (VU), the Natuna Islands tarsier (Tarsius banacus natunensis) is classified as Critically Endangered (CR) and the Belitung Island tarsier (Tarsius banacus saltator) is classified as Endangered (EN) on the IUCN Red List (1).

A bizarre-looking primate, Horsfield’s tarsier (Tarsius banacus) has, like other tarsiers, a number of extraordinary morphological adaptations (2). The unique shape of a tarsier’s spine means that it is capable of rotating its heads nearly 360 degrees (4) (5), while tarsiers are also remarkable in having the biggest eyes of any mammal, relative to their body weight (2). The characteristically large eyes measure around 1.6 centimetres in diameter and weigh around 3 grams, making the volume of one eyeball nearly as big as the volume of the tarsier’s entire brain (2) (5) (6). 

Like other tarsier species, Horsfield’s tarsier has a round head with a reduced muzzle and a rather short neck. The ears are thin and membranous (5). All tarsiers have short forelimbs, but the hind limbs are greatly elongated. In fact, the genus name ‘Tarsius’ and the common name ‘tarsier’ both refer to the elongated tarsal bones in the heel and ankle region, which are longer than those of any other primate (4) (5).

In general, tarsiers have slender fingers and toes with large pads on the ends, which enable them to tightly grasp trees and other surfaces. Like other tarsier species, Horsfield’s tarsier has flattened nails on most of the digits, except for the second and third toes on the hind feed which have claws for grooming (5) (6).

Horsfield’s tarsier is generally buff or grey-brown to brownish, sometimes varying to pale olive or reddish-brown (2) (5) (7). The underparts are buff or greyish (5), and the tail is hairless except for the end, which has a well-developed tuft of hairs (2) (7). The fur of Horsfield’s tarsier is soft and wavy (5) (7).

Horsfield’s tarsier occurs in South East Asia, where it is found in Brunei, Indonesia and Malaysia (1).

Four subspecies are recognised. The subspecies Tarsius bancanus bancanus occurs in south-eastern Sumatra and on the island of Bangka in Indonesia. Tarsius bancanus borneanus occurs in Brunei, Kalimantan and the Karimata Islands, Indonesia, as well as in Sabah, Sarawak and Borneo, Malaysia. Tarsius bancanus natunensis occurs on Serasan in the South Natuna Islands, and possibly nearby on Subi Island, Indonesia.Tarsius bancanus saltator is found only on the island of Belitung, Indonesia (1).

Tarsiers are known to occur in wide variety of habitats (4), and Horsfield’s tarsier may occur in both primary and secondary forest, as well as on the edge of plantations and in shrubby coastal areas (1) (2) (8). However, this species generally appears to prefer secondary forest edges with abundant young saplings and other secondary vegetation (8).

Horsfield’s tarsier is most commonly found in lowland areas below elevations of 100 metres, but has also been recorded up to elevations of 1,200 metres in the Bukit Baka-Bukit Raya National Park in western Kalimantan (1).

Horsfield’s tarsier is extremely agile and almost entirely arboreal (5). The tarsier’s limbs have a number of adaptations for life in the trees, including a unique arrangement of bones in the heel and powerful muscles in the legs which make up almost a quarter of the weight of the entire body (4). As a result, Horsfield’s tarsier is able to leap effortlessly between trees and shrubs, and will cling with ease to vertical objects by rigidly applying its tail for support and grasping with its well-adapted limbs (1) (5). Horsfield’s tarsier is capable of leaping over five metres (4), which is almost 40 times its own body length (2).

Horsfield’s tarsier is nocturnal (1) (4) (5) (7), spending much of the day sleeping in dense vegetation on a vertical branch, or occasionally in a hollow tree (5). Although Horsfield’s tarsier rarely moves on the ground, many of this species’ activities, such as foraging and sleeping, are usually done within two metres of the ground (1) (7).  

Tarsiers are the only entirely carnivorous primates (1) (2) (4). Although Horsfield's tarsier may make frequent, high-pitched calls as it searches for insects, it generally forages for food alone (7). A wide variety of insects are taken, including beetles, grasshoppers, cockroaches, locusts, butterflies, moths, ants and cicadas (1) (2) (4). Horsfield’s tarsier will also take small vertebrates, such as birds, bats, frogs and snakes (1) (2). This species captures its prey by reaching and grabbing it while remaining stationary on a vertical branch, or by leaping onto or towards it (4). In general, tarsiers will eat around 10 percent of their own body weight every 24 hours (2).

Horsfield’s tarsier becomes sexually mature at around a year old, although a young male may sometimes delay reproductive maturity until it is able to establish its own home range. Courtship is usually a rather energetic affair, with much chasing around, often accompanied by soft vocalisations (2).

Breeding occurs throughout the year. The gestation period of Horsfield’s tarsier is around 178 to 190 days (2) (5), which is an unusually long period for such a small mammal (5). The single young is born with its eyes open and a full coat of fur (2) (5). It is able to climb at just a day old (2), but it is around a month before it is able to leap between trees and shrubs (5). The young Horsfield’s tarsier usually clings to the female’s belly until it is weaned, which occurs shortly after it begins to capture its own prey at around 42 days old (5).

Horsfield’s tarsier is territorial, with pairs usually occupying a small home range. The pair will scent mark the territory with urine and a secretion from a gland on the chest (2) (5), and will actively chase and shriek loudly at intruders (5).

Habitat loss due to forest conversion is the biggest threat to Horsfield’s tarsier. Fires, logging and an increasing demand for palm oil, which has led to rapid expansion of oil palm plantations, have destroyed or degraded vast areas of forest in Brunei, Indonesia and Malaysia (1).

Although Horsfield’s tarsier appears to prefer secondary habitats and is able to tolerate some level of habitat disturbance, it does not migrate over long distances. Deforestation of large areas may therefore have an extremely adverse effect on this species’ population (5) (8).

Horsfield’s tarsier is also threatened by collection for the illegal pet trade, especially around Lampung and Way Kambas National Park in Indonesia (1) (5) (8). This species does not generally survive well in captivity when not properly cared for, and usually dies within three days of capture (8). Agricultural pesticides are a further threat to Horsfield’s tarsier (1) (8).

Horsfield’s tarsier is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning that all trade in this species should be carefully monitored (3). It is also protected by law in Indonesia and Malaysia (1).

This species occurs in a number of protected areas, national parks and reserves (1) (8). The subspecies T. b. bancanus occurs in Bukit Barisan Selatan, Kerinci Seblat and Way Kambas National Parks in Indonesia. T. b. borneanus occurs in several protected areas, including Tasek Merimbun Sanctuary in Brunei, Bukit Baka Bukit Raya and Kayan Mentarang National Parks in Indonesia, and Bako, Gunung Malu and Kinabalu National Parks and Sapagaya, Semengo and Sepilok Forest Reserves in Malaysia. T. b. saltator and T. b. natunensis do not occur in any protected areas (1).

Find out more about tarsiers:

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  1. IUCN Red List (September, 2011)
    http://www.iucnredlist.org/
  2. Macdonald, D.W. (2006) The Encyclopedia of Mammals. Oxford University Press, Oxford.
  3. CITES (September, 2011)
    http://www.cites.org/
  4. Primate Info Network - Tarsiers (September, 2011)
    http://pin.primate.wisc.edu/factsheets/entry/tarsier
  5. Nowak, R.M. (1991) Walker’s Mammals of the World. The Johns Hopkins University Press, Baltimore and London.
  6. Ankel-Simons, F. (1999) Primate Anatomy: An Introduction. Academic Press, San Diego, California.
  7. Forestry Department, Sarawak - Western tarsier (September, 2011)
    http://www.forestry.sarawak.gov.my/forweb/wildlife/mgmt/tpa/wtrasier.htm
  8. Wolfheim, J.H. (1983) Primates of the World: Distribution, Abundance and Conservation. University of Washington Press, London.