Biology
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Hose's langur is a diurnal species with a primarily folivorous diet, equipped with a specialised sacculated stomach and enlarged salivary glands to assist in the breakdown of tough leaf material. However, the species will also feed on fruits, seeds and flowers, as well as on the eggs and nestlings of birds such as the gray-throated babbler (Stachyris nigriceps) (3).
In Sabah and Brunei, group sizes tend to range from six to eight individuals, although 12 or more have reported from Temburong and solitary individuals do occur (3) (7). Groups contain one adult male and two or more adult females, and mating is polygynous (3) (7). Hose's langurs give birth to single offspring (3), which are weaned by one year and fully mature by four to five (5), with males dispersing from their natal groups (7).
Conservation
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Hose's langur is fully protected in Sarawak, prohibiting individuals from keeping them as pets, or hunting, capturing, killing, selling, importing or exporting them, with stiff penalties of a fine and two years imprisonment if caught (7). The species appears in a few protected areas, such as Kutai National Park and Kayan Mentarang National Park, but the protection offered is frequently inadequate and laws remain unenforced. Indeed, despite being found in national parks, only an estimated 5% of the Kutai National Park forest has escaped logging, illegal settling, industrial development and fire (6), and active protection of Kayan Mentarang National Park has clearly been lacking, having suffered heavily from hunting pressure (8). In such cases, National Park 'protection' alone does not guarantee preservation, and more active protection of wildlife against hunting and habitat destruction is desperately required to prevent the extinction of this species. Sadly, it may already be too late for certain subspecies.
Description
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Hose's langur is a relatively small, slim-built primate (5), characterised by a high forehead and a prominent, forward-leaning crest down the centre of the crown (3) (6). The colour of the coat varies with the subspecies, but is predominantly grey on the back, white on the stomach and chest, and blackish on the hands and feet. The face is pink, with a distinct black band marking each cheek. Infants are easily distinguished, being white with black lines down the back and across the shoulders (3). Groups (probably the adult male) sometimes give a unique gargling call (7).
Habitat
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This arboreal monkey largely moves through the middle levels of the forest canopy, occasionally descending to the ground to visit natural mineral sources (3). Primary and, less abundantly, secondary forests are inhabited, in an altitudinal range of 1,000-1300 m. The species will also occasionally enter plantations (3) (7).
Range
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Endemic to the island of Borneo (6), in the countries of Brunei Darussalam, Indonesia (Kalimantan), and Malaysia (provinces of Sarawak and Sabah) (1). P. h. hosei occurs in Sarawak (1), but may only be found around the lower Baram river (3). P. h. everetti is found along the northwest coast of Sabah into Brunei, while P. h. sabana is confined to central and eastern Sabah and south-western to Kalabakan (3). This subspecies may also be found in far north-eastern Kalimantan. P. h. canicrus is recorded definitely only from Gunung Talisayan and Karangan in East Kalimantan, but is probably also present in Kutai (7).
Status
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Classified as Data Deficient (DD) on the IUCN Red List 2004 (1) and listed under Appendix II of CITES (4). Four subspecies are recognised: Hose's grizzled langur (P. h. hosei), Everett's grizzled langur (P. h. everetti) and the Miller's grizzled langur (P. h. canicrus) are all classified as Data Deficient while the crested grizzled langur or saban grizzled langur (P. h. sabana) is classified as Vulnerable (VU A2c) on the IUCN Red List 2004 (1).
Threats
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Hunting and deforestation pose critical threats to this species across its range. Indeed, the reputed medicinal value of the 'bezoar' stones sometimes formed in the monkey's guts makes this species a target even for hunters uninterested in its meat (6). Interviews with local hunters indicate that hunting for these bezoar stones was the primary reason for the 50 – 80% decline recorded for the species between 1996 and 2003 in Kayan Mentarang National Park, East Borneo, where the forest has remained in fairly pristine condition (8). In this case, a merchant calling at a nearby village in 1998 had reportedly guaranteed to purchase them, sparking excessive hunting of Hose's langur in the area, to such an extent that 3 years later this hunting was no longer economically viable (8). As a result of habitat loss and hunting pressure, Miller's grizzled langur (P. h. canicrus) is thought to be critically endangered, or even extinct. Thus, it is listed as one of the world's 25 most endangered species, although no quantitative surveys have yet been undertaken. Hose's grizzled langur (P. h. hosei) is considered by many to be in a worse predicament and even more likely to be extinct, although there is a small chance that it exists in the northern part of the Similajau National Park in central coastal Sarawak. Populations may also exist in Brunei, which has suffered much less hunting and deforestation, but hybridization with Everett's grizzled langur (P. h. everetti) could be a potential issue in this area (6).
Hose's langur
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Hose's langur (Presbytis hosei) is a species of primate in the family Cercopithecidae endemic to the island of Borneo, including Brunei, Kalimantan (Indonesia), and East Malaysia. Its natural habitat is subtropical or tropical dry forests. It is threatened by habitat loss.[2] It was first identified in Kutai National Park and Sangkulirang Peninsula, East Kalimantan, Indonesia, in 1985.
Miller's langur (P. canicrus) and the Saban grizzled langur (P. sabana) were previously considered subspecies of Hose's langur.[3][4] There used to also be two additional forms that were considered separate subspecies, P. h. hosei and P. h. everetti. However, P. h. everetti is no longer considered to be a separate subspecies as the original identification of it as a separate subspecies appears to be the result of comparing a subadult female with an adult male.[5][6]
Threatened extinction
In 1996, Hose's langurs of East Kalimantan, Indonesia, were among the most common primates in the area. In 2003, their population densities have decreased by 50–80%.[7] The sudden drop in population arises from the rising demand for its bezoar stones and to prevent crop raiding, and the rapid deforestation and removal of the primate's habitat.
Densities of Hose's langurs positively correlate with tree height, height of the first bough, tree diameter, and canopy cover, and negatively with vegetation cover at low and ground level. With the constant deforestation and destruction of its habitat, Hose's langurs continue to lose their habitat. Every known area in which the primate resides has been affected severely, with the exception of the innermost areas of forests that have been relatively untouched by humans.[8]
References
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^ Groves, C. P. (2005). Wilson, D. E.; Reeder, D. M. (eds.). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Baltimore: Johns Hopkins University Press. p. 171. ISBN 0-801-88221-4. OCLC 62265494.
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^ a b Nijman, V.; Traeholt, C.; Setiawan, A.; Cheyne, S. (2021). "Presbytis hosei". IUCN Red List of Threatened Species. 2021: e.T175648870A195370322. doi:10.2305/IUCN.UK.2021-1.RLTS.T175648870A195370322.en. Retrieved 17 November 2021.
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^ "Presbytis canicrus". American Society of Mammalogists. Retrieved 10 April 2020.
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^ "Presbytis sabana". American Society of Mammalogists. Retrieved 10 April 2020.
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^ Groves, Colin; Roos, Christian (2013). Mittermeier, Russell A.; Rylands, Anthony B.; Wilson, Don E. (eds.). Handbook of Mammals of the World: Volume 3. pp. 716–717. ISBN 978-8496553897.
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^ Phillipps, Quentin; Phillipps, Karen (2016). Phillipps' Field Guide to the Mammals of Borneo. Princeton University Press. pp. 164–165. ISBN 9780691169415.
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^ Vincent Nijman Decline of the endemic Hose's langur Presbytis hosei in Kayan Mentarang National Park, East Borneo April 2005. Retrieved 26 October 2012
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^ Vincent Nijman Effects of habitat disturbance and hunting on the density and the biomass of the endemic Hose's leaf monkey Presbytis hosei (Thomas, 1889) (Mammalia: Primates: Cercopithecidae) in east Borneo 2004. Retrieved 26 October 2012
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Hose's langur: Brief Summary
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Hose's langur (Presbytis hosei) is a species of primate in the family Cercopithecidae endemic to the island of Borneo, including Brunei, Kalimantan (Indonesia), and East Malaysia. Its natural habitat is subtropical or tropical dry forests. It is threatened by habitat loss. It was first identified in Kutai National Park and Sangkulirang Peninsula, East Kalimantan, Indonesia, in 1985.
Miller's langur (P. canicrus) and the Saban grizzled langur (P. sabana) were previously considered subspecies of Hose's langur. There used to also be two additional forms that were considered separate subspecies, P. h. hosei and P. h. everetti. However, P. h. everetti is no longer considered to be a separate subspecies as the original identification of it as a separate subspecies appears to be the result of comparing a subadult female with an adult male.
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