Proboscis monkey

Life span: >25 years (captive) Total population: Unknown Regions: Borneo Gestation: 166-200 days Height: 73 to 76 cm (M), 61 to 64 cm (F) Weight: 20 kg (M), 10 kg (F)

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MORPHOLOGY

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).

RANGE

CURRENT RANGE MAPS (IUCN REDLIST): Nasalis larvatus 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).

HABITAT

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).

ECOLOGY

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.