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Species: N. larvatus
Other names: long-nosed monkey; næseabe (Danish); neusaap (Dutch); Nenäapina (Finnish); nasique (French); bekantan, bangkatan, monyet belanda (Indonesian); mono narigudo, násico (Spanish); näsapa (Swedish).
Total population: Unknown
Gestation: 166-200 days
Height: 73 to 76 cm (M), 61 to 64 cm (F)
Weight: 20 kg (M), 10 kg (F)
Proboscis monkeys are among the larger colobines and are sexually dimorphic, with males’ head-body length measuring 75.5 cm (29.7 in) (range 73-76 cm (28.7-29.9 in)), and females measuring 62 cm (24.4 in)(range 61-64 cm (24.0-25.2 in)) (Napier & Napier 1985; Bennett & Sebastian 1988; Ankel-Simons 2007). Males weigh around 20kg (44.1 lb) while females weigh half of that (Napier & Napier 1985; Bennett & Gombek 1993). The face of adults is orange-pink. Females have a very large nose for a primate, but the noses of males dwarf even those of the females and often hang lower than the mouth (Payne et al. 1985; Ankel-Simons 2007). The nose of an adult male can exceed 10cm (3.9 in) in length (Ellis 1986). Overall, the pelage is somewhat long, and is bright orange, reddish brown, yellowish brown, or brick-red dorsally (Kern 1964; Payne et al. 1985; Groves 2001; Ankel-Simons 2007). The ventral surfaces are light-gray, yellowish, or grayish to light-orange (Kern 1964; Payne et al. 1985; Ankel-Simons 2007). The penis is red and the scrotum is black. Several of the toes are webbed (Kern 1964; Ankel-Simons 2007). Adult males have a dark brown mane on their back (Bennett & Gombek 1993). The species possesses large ischial callosities and both sexes look perpetually pregnant, due to oversized, protruding stomachs (Bennett & Gombek 1993; Groves 2001; Ankel-Simons 2007).
Proboscis monkeys are avid swimmers, capable of swimming up to 20m (65.6 ft) completely submerged, and may leap from high branches into water (Kern 1964; Bennett & Sebastian 1988; Boonratana 1993). In fact, among the primates they have the most aquatic lifestyle, and often swim across rivers (Yeager 1989b; Sebastian 2000). Depending on the habitat type, proboscis monkeys are predominantly arboreal and occasionally terrestrial; moving quadrupedally and through leaping (Kawabe & Mano 1972; Napier & Napier 1985). Modes of locomotion include semi-brachiation, climbing, leaping, quadrupedal and suspensory movement and rare bipedalism (Ramesh Boonratana pers comm.).
In captivity, proboscis monkeys have lived over 25 years (Weigl 2005).
CURRENT RANGE MAPS (IUCN REDLIST):
Proboscis monkeys are only found on Borneo, and in parts of all three nations that divide the island; Brunei, Indonesia, and Malaysia (Bennett & Sebastian 1988; Brandon-Jones et al. 2004). They are not found throughout the island however, and are often concentrated in coastal regions. Inland, they are seen along rivers that are scattered throughout the Bornean interior, sometimes over 200 km (124.3 mi), from the coast (Bennett & Gombek 1993; Meijaard & Nijman 2000a). They are not present in much of the Bornean rainforest and much of their distribution within Borneo is unknown (Bennett & Gombek 1993).
Proboscis monkeys are only found in lowland habitats including several types of coastal and riparian habitats, many that are tidally flooded (Kawabe & Mano 1972; Salter et al. 1985; Sebastian 2000). The species is generally not found above 200 m (656.2 ft) above sea level (Meijaard & Nijman 2000a). Habitats are usually near water or rivers, as proboscis monkeys rarely range more than a kilometer from water and sleep predominantly but not exclusively near it (Salter et al. 1985; Ruhiyat 1986; Yeager 1989a; Bennett & Gombek 1993; Boonratana 2000; review in Sebastian 2000; Onuma 2002). The species is also found in wetlands not directly connected with the coast (Sebastian 2000). Preferred habitats include certain dipterocarp forests, mangrove forest, or riverine forest (Salter & Aken 1983; Salter et al. 1985; Yeager 1989a; Benett & Gombek 1993; Sebastian 2000; Tuen & Pandong 2007). When both are available, tall forests are preferred over tidal or coastal habitats (Salter et al. 1985; Sebastian 2000). Availability of food is a strong factor in habitat choice, and in some cases, where high forest is unavailable, tidal forests are preferred (Salter et al. 1985). Several other types of proboscis habitat include dwarf swamp forest, stunted swamp forest, rubber forest, rubber plantations, limestone hill forest, nipa swamp, nibong swamp, and tall swamp forest as well as tropical heath forest and steep cliffs (Salter et al. 1985; see Sebastian 2000; Onuma 2002; Soendjoto 2004; Tuen & Pandong 2007). Occasionally, degraded tidal forests, logged peat swamps and logged high forest are utilized (Salter et al. 1985). More rarely, proboscis monkeys are also found in nipa vegetation or scrubby vegetation found on rocky headlands and exposed cliffs and have even been seen on agricultural land (Salter & Aken 1983; Salter et al. 1985). Proboscis monkeys may be precluded from living in many Bornean inland and hill forests by nutritional or food requirements that such habitat types cannot provide (Bennett & Sebastian 1988). In one study at Samunsam Wildlife Sanctuary in western Borneo, habitat use is seasonal, with a wider range of habitat types used during the wet season (November) as opposed to the dry season (August) (Tuen & Pandong 2007).
At the long-term study site at the Tanjung Putting National Park in southern Borneo, average temperatures remained relatively constant year-round, with highs averaging around 29°C (84.2°F) and lows averaging 22°C (71.6°F). Here, over 15 cm (5.9 in) of rain fell monthly, but less fell between July and October than during the rest of the year (Yeager 1989b). At a different study site in northern Borneo in eastern Sabah, temperatures were also relatively constant year-round, ranging from average lows of 23.7°C (74.7°F) to average highs around 33°C (91.4°F) (Boonratana 1993). Recorded annual rainfall totals at this site ranged from around 182 cm (71.7 in) to 298 cm (117.3 in) (Boonratana 1993).
Proboscis monkeys are seasonal folivore/frugivores, eating foods from over 90 species of plant including predominantly fruit and leaves (Salter et al. 1985; Boonratana 1993; Yeager 1989a). Annually, they consume fruits (40.33%), and flowers (2.97%) in addition to leaves (51.94%), insects and bark (<1%) and unknown foods (4.68%) (Yeager 1989a). Boonratana (1993; 2003) gives the following food data: mature leaves (0.3%), young leaves (72.7%), unripe fruits (6.6%), ripe fruits (1.7%), seeds (2.4%), flowers (7.8%), flower buds (0.5%), and unknown items (8.0%). Leaves that are eaten are usually young (although other parts are eaten as well), and of the fruit, seeds and flesh/seeds make up the majority of the consumed parts (Ruhiyat 1986; Yeager 1989a; Boonratana 1993). Ferns are also sometimes eaten and crops such as bananas are raided (Soendjoto 2004; Agoramoorthy 2007). Rarely, proboscis monkeys will drink directly from rivers (Boonratana 1993). Seasonally, there are shifts in food consumption; from mostly fruit (January-May) to mostly leaves (June-December) (Yeager 1989a).
Home ranges overlap extensively with those of other groups, but territorial behavior is largely absent (Yeager 1989a; Bennett & Gombek 1993; Boonratana 1993; 2000). Recorded group home ranges usually vary between 1.3 and 9 km² (0.5 and 3.5 mi²) with similar estimates in other studies (Kawabe & Mano 1972; Salter et al. 1985; Yeager 1989a; Bennett & Gombek 1993; Boonratana 1993; see review in Boonratana 2000). Home range size variation can be attributed to population densities and habitat type (Sebastian 2000). Day ranges average 910 m-2000 m (2985.6-6561.7 ft) (Salter et al. 1985; Bennett & Gombek 1993; Boonratana 2000). In habitats associated with rivers, proboscis monkeys usually sleep by the river and move inland during the day, and then back to the river late in the day (Salter et al. 1985; Rajanthan & Bennett 1990). However, they never move more than a kilometer away from water (Salter et al. 1985; Ruhiyat 1986; review in Sebastian 2000).
Groups usually sleep in one or several nearby trees (Yeager 1990b).
Daily, predominant activities include resting, traveling, vigilance, and feeding (Salter & Aken 1983; Boonratana 1993). Upon awakening, proboscis monkeys will generally feed then move inland and rest. The majority of the day is spent feeding, resting, and traveling and at dusk, the animals will move back to the riverside and feed before dark (Bennett & Gombek 1993). On a daily basis, feeding peaks in the morning and at dusk (Boonratana 1993).
The false gavial (Tomistoma schlegeli), a crocodile-like reptile, is a major predator of proboscis monkeys and has been seen taking adult males and immature individuals from low branches over water (Galdikas 1985; Yeager 1989b; 1991). Another predator is the clouded leopard (Neofelis nebulosa) which has also been seen attacking the monkeys, especially immature individuals (Kern 1964; Matsuda et al. 2008a). In mid-1992, a clouded leopard with a freshly killed adult male proboscis monkey was seen and photographed (J. C. Prudente pers comm. cited in Boonratana 1993). Monitor lizards and pythons are potential predators, as well as estuarine crocodiles (Crocodylus porosus), and crested serpent eagles (Spilornis cheela) all of which can potentially take infants and young juveniles (Yeager 1989b; 1991; Sebastian 2000). When crossing rivers, the species will do so at narrows or areas where the crossing can be completed arboreally, possibly to avoid predation (Yeager 1991; Matsuda et al. 2008b).
Proboscis monkeys can be sympatric with a number of other primate species; as is the case in eastern Sabah, where the species is sympatric with Presbytis hosei, P. rubicunda, Hylobates muelleri, Pongo pygmaeus, Trachypithecus cristatus, Macaca nemestrina, M. fascicularis, Nycticebus coucang, and Tarsius bancanus. In fact, this is one of only two sites in the world that four species of colobine call home (Boonratana 1993). If a sympatric primate species is encountered, the other species is usually ignored, although both long-tailed macaques and orangutans displace proboscis monkeys at feeding sites (Yeager 1989a; Rajanthan & Bennett 1990). There is potential competition with long-tailed macaques (Macaca fascicularis) due to food resource overlap, especially between January-June and November-December (Yeager 1989a).
Content last modified: February 25, 2009
Written by Kurt Gron. Reviewed by Ramesh Boonratana.
Cite this page as:
Gron KJ. 2009 February 25. Primate Factsheets: Proboscis monkey (Nasalis larvatus) Taxonomy, Morphology, & Ecology . <http://pin.primate.wisc.edu/factsheets/entry/proboscis_monkey/taxon>. Accessed 2020 July 14.
For individual primate species conservation status, please search the IUCN Red List.
Also search the current scientific literature for primate conservation status (overall as well as for individual species), and visit CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora).
Conservation information last updated in 2009 follows, for comparison:
It is very difficult to keep proboscis monkeys in captivity and few zoos have been successful. However, with very careful husbandry, it is possible keep proboscis monkeys in captivity and thus there is potential for ex situ conservation (Agoramoorthy et al. 2004). Proboscis monkeys are particularly threatened because one of their preferred habitats is coastal lowland forests, locations which are also often preferentially developed or cultivated by people. In sum, most of their habitat is threatened or already disturbed (Sebastian 2000). Compounding the problem, most proboscis monkeys are found outside of protected reserves (Boonratana & Sharma 1992).
Threat: Human-Induced Habitat Loss and Degradation
As with many primate species, habitat loss is a major threat to proboscis monkeys and much of their former habitat has already been lost (Bennett 1988; Boonratana & Sharma 1992; Sebastian 2000). In addition, extensive proboscis habitats are being targeted for development, as is the case in Central Kalimantan, Indonesia (Meijaard & Nijman 2000a). Human land use, including clearance for agriculture, plantation development (including for coca and oil palm production), mining, for human resettlement and for industrial sites, as well as burning, swamp reclamation, commercial aquaculture (fish and shrimp farming), and logging destroys habitats and also isolates populations from one another (Bennett 1988; Boonratana & Sharma 1992; Yeager 1992a; Sebastian 2000; Meijaard & Nijman 2000a; Soendjoto 2004; Agoramoorthy 2007). These problems are also made worse by access roads, which fragment populations and increases inbreeding (Soendjoto 2004). Also, many plantations have electric fences around them, which may prevent normal proboscis monkey ranging (Boonratana & Sharma 1992). Selective logging sometimes destroys preferred sleeping and feeding trees (Yeager 1992a). After logging, forests are sometimes poisoned to prevent undesirable vegetation from regrowing with the goal of increasing timber productivity as the forest regenerates. This likely affects proboscis monkeys adversely and prevents them from living in those habitats (Bennett 1988). In addition, human immigration from other areas is increasing land use and other sources of disturbance (Sebastian 2000).
Threat: Harvesting (hunting/gathering)
In some areas, proboscis monkeys are persecuted as crop raiders and are poisoned. In some regions, they are hunted for food, and in others, they are hunted recreationally, and as bait or feed for lizards, snakes and crocodiles (Bennett et al. 1987; Bennett 1988; Boonratana & Sharma 1992; Meijaard & Nijman 2000a; Soendjoto 2004). Hunting has already significantly reduced proboscis monkey numbers at some localities (Meijaard & Nijman 2000a). Also, even though they might not be the target species, firearm hunting of other game has the potential to disturb proboscis monkeys and alter their behavior (Tuen & Pandong 2007). However, hunting for food and persecution as crop pests is not always the case, as local Muslim inhabitants will not eat monkey meat for religious reasons (Boonratana & Sharma 1992). Proboscis monkeys are also kept illegally as pets (Meijaard & Nijman 2000b). Their sleeping habits near rivers also make them especially susceptible to hunting from boats (Tuen & Pandong 2007).
In riverine areas of increased human activity, pollution may increase, especially due to spilled oil and fuel from boats, but also from human septic waste (Yeager 1992a). All of these types of pollution have the potential to alter proboscis monkey habitats.
Threat: Natural Disasters
Natural droughts increase the susceptibility of proboscis monkey habitats to destructive fires (Yeager 1992a).
Threat: Human Disturbance
Summertime activities of humans, such as fishing, fish-salting and smoking, trapping, and encampments, all disturb proboscis monkeys, keeping them away from preferred areas along rivers. Other activities that also disturb proboscis monkeys include rattan collection, the collection of honey from bees, and firewood gathering (Sebastian 1994 cited in Sebastian 2000). Further, increasing boat traffic, sometimes as a result of gold extraction along rivers, disturbs proboscis river crossing behavior and causes declines in population density and group size. Also, increased boat traffic threatens proboscis monkeys due to the potential for collisions while they are crossing rivers (Yeager 1992a). In Sabah, some proboscis monkey populations are threatened by unmanaged tourism (Ramesh Boonratana pers comm.).
LINKS TO MORE ABOUT CONSERVATION
- No current links for Nasalis larvatus
- Links for all species
- Can Heavily Deforested Sebangau National Park Be Saved? (Jakarta Globe; July 21, 2012)
- Wildlife official: palm oil plantations behind decline in proboscis monkeys (Mongabay; December 5, 2011)
- Animals of the Disappearing Mangroves (Scientific American; July 3, 2009)
- Malaysia: Face to face with orangutans (Salt Lake Tribune; November 11, 2008)
- Proboscis monkeys also found in Pulau Gaya (Daily Express, Malaysia; April 2, 2008)
- Endangered monkeys found in Indonesia (The Hindu; September 10, 2007)
- Sebangau National Park in need of all-inclusive management (Jakarta Post; September 11, 2007)
- Links for all species
ORGANIZATIONS INVOLVED IN Nasalis larvatus CONSERVATION
Content last modified: February 25, 2009
Written by Kurt Gron. Reviewed by Ramesh Boonratana.
Cite this page as:
Gron KJ. 2009 February 25. Primate Factsheets: Proboscis monkey (Nasalis larvatus) Conservation . <http://pin.primate.wisc.edu/factsheets/entry/proboscis_monkey/cons>. Accessed 2020 July 14.
The following references were used in the writing of this factsheet. To find current references for Nasalis larvatus, search PrimateLit.
Agoramoorthy G. 2007. Conservation status of proboscis monkeys in disturbed mangrove forests in Sabah, northern Borneo. Tigerpaper 34(3):1-4.
Agoramoorthy G, Hsu MJ. 2004. Occurrence of infanticide among wild proboscis monkeys (Nasalis larvatus) in Sabah, Northern Borneo. Folia Primatol 76(3):177-9.
Ankel-Simons F. 2007. Primate Anatomy: an introduction, 3rd Edition. San Diego: Elsevier Acad Pr. 724 p.
Bennett EL, Caldecott JO, Kavanagh M, Sebastian AC. 1987. Current status of primates in Sarawak. Primate Conserv 8:184-6.
Bennett EL. 1988. Proboscis monkeys and their swamp forests in Sarawak. Oryx 22(2):69-74.
Bennett EL, Gombek F. 1993. Proboscis monkeys of Borneo. Sabah (MY):Koktas Sabah Berhad Ranau. 75p.
Bennett EL, Sebastian AC. 1988. Social organization and ecology of Proboscis monkeys (Nasalis larvatus) in mixed coastal forest in Sarawak. Int J Primatol 9(3):233-55.
Boonratana R, Sharma DS. 1992. Conservation of proboscis monkeys in the lower Kinabatangan, Sabah. In: Thierry B, Anderson JR, Roeder JJ, Herrenschmidt N, editors. Current primatology, volume I: ecology and evolution. Strasbourg (FR):Universite Louis Pasteur. p93-100.
Boonratana R. 1999. Dispersal in proboscis monkeys (Nasalis larvatus) in the lower Kinabatangan, Northern Borneo. Tropic Biodiv 6(3):179-87.
Boonratana R. 1993. The ecology and behaviour of the proboscis monkey (Nasalis larvatus) in the lower Kinabatangan, Sabah. PhD dissertation, Mahidol University. 275p.
Boonratana R. 2003. Feeding ecology of proboscis monkeys (Nasalis larvatus) in the lower Kinabatangan, Sabah, Malaysia. Sabah Parks Nat J 6:1-26.
Boonratana R. 2000. Ranging behavior of proboscis monkeys (Nasalis larvatus) in the lower Kinabatangan, northern Borneo. Int J Primatol 21(3):497-518.
Boonratana R. 2002. Social ooranisation of proboscis monkeys (Nasalis larvatus) in the lower Kinabatangan, Sabah, Malaysia. Malay Nat J 56(1):57-75.
Brandon-Jones D, Eudey AA, Geissmann T, Groves CP, Melnick DJ, Morales JC, Shekelle M, Stewart C-B. 2004. Asian primate classification. Int J Primatol 25(1):97-164.
Ellis D. 1986. Proboscis monkey and aquatic ape. Sarawak Mus J 36(57):251-62.
Galdikas BMF. 1985. Crocodile predation on a proboscis monkey in Borneo. Primates 26(4):495-6.
Gorzitze AB. 1996. Birth-related behavior in wild proboscis monkeys (Nasalis larvatus). Primates 37(1):75-8.
Griner LA. 1980. East Bornean proboscis monkey, Nasalis larvatus orientalis. Zool Gart 50:73-81.
Groves C. 2001. Primate taxonomy. Washington DC: Smithsonian Inst Pr. 350 p.
Hollihn U. 1973. Remarks on the breeding and maintenance of colobus monkeys Colobus guereza, proboscis monkeys Nasalis larvatus and douc langurs Pygathrix nemaeus in zoos. Int Zoo Yearb 13:185-8.
Kawabe M, Mano T. 1972. Ecology and behavior of the wild proboscis monkey, Nasalis larvatus (Wurmb) in Sabah, Malaysia. Primates 13(2):213-28.
Kern JA. 1964. Observations on the habits of the proboscis monkey, Nasalis larvatus (Wurmb), made in the Brunei Bay area, Borneo. Zoologica 49:183-92.
Macdonald DW. 1982. Notes on the size and composition of groups of proboscis monkey, Nasalis larvatus. Folia Primatol 37:95-8.
Matsuda I, Tuuga A, Higashi S. 2008a. Clouded leopard (Neofelis diardi) predation on proboscis monkeys (Nasalis larvatus) in Sabah, Malaysia. Primates 49(3):227-31.
Matsuda I, Tuuga A, Akiyama Y, Higashi S. 2008b. Selection of river crossing location and sleeping site by proboscis monkeys (Nasalis larvatus) in Sabah, Malaysia. Am J Primatol 70(11):1097-101.
Meijaard E, Nijman V. 2000a. Distribution and conservation of the proboscis monkey (Nasalis larvatus) in Kalimantan, Indonesia. Biol Conserv 92(1):15-24.
Meijaard E, Nijman V. 2000b. The local extinction of the proboscis monkey Nasalis larvatus in Pulau Kaget Nature Reserve, Indonesia. Oryx 34(1):66-70.
Messeri P, Trombi M. 2000. Vocal repertoire of proboscis monkey (Nasalis larvatus, L.) in Sarawak. Folia Primatol 71(4):268-87.
Murai T, Mohamed M, Bernard H, Mahedi AP, Saburi R, Higashi S. 2007. Female transfer between one-male groups of proboscis monkey (Nasalis larvatus). Primates 48(2):117-21.
Murai T. 2006. Mating behaviors of the proboscis monkey (Nasalis larvatus). Am J Primatol 68(8):832-7.
Murai T. 2004. Social behaviors of all-male proboscis monkeys when joined by females. Ecol Res 19(4):451-4.
Onuma M. 2002. Daily ranging patterns of the proboscis monkey, Nasalis larvatus, in coastal areas of Sarawak, Malaysia. Mammal Study 27(2):141-4.
Payne J, Francis CM, Phillips K. 1985. A field guide to the mammals of Borneo. Kuala Lumpur (MY): World Wildlife Fund Malaysia & The Sabah Society.
Pournelle GH. 1967. Observations on reproductive behaviour and early postnatal development of the proboscis monkey Nasalis larvatus orientalis. Int Zoo Yearb 7:90-2.
Rajanathan R, Bennett EL. 1990. Notes on the social behaviour of wild proboscis monkeys (Nasalis larvatus). Malay Nat J 44(1):35-44.
Ruhiyat Y. 1986. Preliminary study of proboscis monkey (Nasalis larvatus) in Gunung Palung Nature Reserve, West Kalimantan. Kyoto U Overseas Res Rep Studies Asian Non-Hum Prim 5:59-69.
Salter RE, MacKenzie NA, Nightingale N, Aken KM, Chai PK P. 1985. Habitat use, ranging behaviour, and food habits of the proboscis monkey, Nasalis larvatus (van Wurmb), in Sarawak. Primates 26(4):436-51.
Salter RE, Aken KM. 1983. The proboscis monkey in Bako National Park, Sarawak. Tigerpaper 10(3):6-8.
Schultz AH. 1942. Growth and development of the proboscis monkey. Bull Museum Comp Zool Harvard U 89:279-314.
Sebastian AC. 2000. Proboscis monkeys in Danau Sentarum National Park. Borneo Res Bull 31:359-71.
Soendjoto MA. 2004. A new record on habitat of the proboscis monkey (Nasalis larvatus) and its problems in south Kalimantan, Indonesia. Tigerpaper 31(2):17-8.
Tuen AA, Pandong JJAG. 2007. Habitat use and population density of proboscis monkeys (Nasalis larvatus) at Samunsam Wildlife Sanctuary, Sarawal. Malay Nat J 59(3):269-79.
Weigl R. 2005. Longevity of mammals in captivity; from the living collections of the world. Stuttgart (DE): E. Schweizerbartsche. 214 p.
Yeager CP. 1992a. Changes in proboscis monkey (Nasalis larvatus) group size and density at Tanjung Putting National Park, Kalimantan Tengah, Indonesia. Trop Biodiv 1(1):49-55.
Yeager CP. 1995. Does intraspecific variation in social systems explain reported differences in the social structure of the proboscis monkey (Nasalis larvatus)? Primates 36(4):575-82.
Yeager CP. 1989a. Feeding ecology of the proboscis monkey (Nasalis larvatus). Int J Primatol 10(6):497-530.
Yeager CP. 1991. Possible antipredator behavior associated with river crossings by proboscis monkeys (Nasalis larvatus). Am J Primatol 24(1):61-6.
Yeager CP. 1989b. Proboscis monkey (Nasalis larvatus) social organization and ecology. PhD dissertation, University of California-Davis. 140p.
Yeager CP. 1990a. Notes on the sexual behavior of the proboscis monkey (Nasalis larvatus). Am J Primatol 21(3):233-7.
Yeager CP. 1990b. Proboscis monkey (Nasalis larvatus) social organization: group structure. Am J Primatol 20(2):95-106.
Yeager CP. 1992b. Proboscis monkey (Nasalis larvatus) social organization: nature and possible functions of intergroup patterns of association. Am J Primatol 26(2):133-7.
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