The average body mass for an adult male proboscis monkey is between 16 and 22 kilograms, and for the females it is between 7 and 12 kilograms. This is a sexually dimorphic species, especially in body size (Kern, 1964). The males of this species has a large pendulous nose which is smaller and more turned up in females. This nose of the male assists in enhancing vocalizations, acting as an organ of resonance (Ankel-Simons, 2000). The proboscis monkey has interdigital webbing, and may be an adaptation for swimming. The pelage color is pink and brown with red around the crown, nape, and shoulders, and with gray on the arms, legs, and tail (Kern, 1964). There are cream-colored patches on the cheeks and throat. The males have a black colored scrotum and a penis that is red in color (Ankel-Simons, 2000). When the infants are born their faces are a vivid blue color (Pournelle, 1967). At age 2.5 months the facial color of the infant darkens to a sooty dark gray color, and then at 8.5 months the gray color starts to lighten to the flesh color of the adult (Pournelle, 1967).
The proboscis monkey is found on the island of Borneo. This species prefers to live in nipa-mangrove-mixed forest, mangrove forest, and lowland forest (Kawabe and Mano, 1972). In Sarawak it was found that this species prefers to live in riverain and mixed diterocarp/high kerangas forests (Salter et al., 1985). It has been suggested that this species is restricted to the coastal areas and areas nears rivers because the interior has soils that are low in minerals and salts, which are needed in the diet (Bennett and Sebastian, 1988). This species avoids areas with heavy deforestation, such as agricultural land (Salter et al., 1985).
|Group sizes range from 3 to 32 individuals. This is not a territorial species, with group ranges overlapping many groups (Kawabe and Mano, 1972; Boonratana, 2000). Groups of proboscis monkeys will usually never move father than 600 meters from a river or stream (Bennett and Sebastian, 1988). The greatest times of activity for this species is from late afternoon to dark (Kern, 1964; Ruhiyat, 1986). Groups will move away from the riverain forest in the morning and into the tree mangrove forest in the afternoon, and back to the riverain forest in the evening (Salter et al., 1985; Boonratana, 2000). This species has a high dependency on habitats that adjoin rivers (Boonratana, 2000). At Sukau, in Northern Borneo, was found to travel at a mean height of 12.25 meters, and at Abai the mean height for traveling was found to be 6.91 meters (Boonratana, 2000). This a diurnal and semi-terrestrial species.
It was found that in Brunei Bay that the favorite sleeping tree for the proboscis monkey is the pedada, Sonneratia alba (Kern, 1964). Kern (1964) suggests that this tree species is chosen because the upper branches protect the monkeys from predators during the night. This species is always found to sleep near rivers, 0 to 15 meters from the river's edge (Ruhiyat, 1986). At Gunung Palung Nature Reserve the favorite trees used for sleeping were the dungun, Heritiera sp. and the pisang-pisang, Mezzetia parviflora (Ruhiyat, 1986). This species will rarely sleeping in the same tree on consecutive nights (Ruhiyat, 1986). When leaving sleeping trees, males are usually the last individuals to leave (Yeager, 1990a). When sleeping the all-male groups tend to be more spread out in the trees than the unimale groups (Rajanathan and Bennett, 1990).
growls: These calls are made by adult males and this functions to calm another member of group down.
honks: These calls are made by adult males of the group. This functions as an aggressive call which threats other members of the group, and is also made in the presence of predators.
shrieks: These calls are given by juveniles of both sexes and adult females. This is emitted when the individual is agitated or excited.
scream: This vocalization is heard during agonistic interactions (Ruhiyat, 1986). This call is heard during feeding bouts and at night during sleep (Ruhiyat, 1986).
Ankel-Simons, F. 2000. Primate Anatomy: An Introduction. Academic Press: San Diego.
Bennett, E.L. and Sebastian, A.C. 1988. Social organization and ecology of proboscis monkeys (Nasalis larvatus) in mixed coastal forest in Sarawak. International Journal of Primatology. Vol. 9, 233-255.
Boonratana, R. 1994. The ecology and behaviour of the proboscis monkey (Nasalis larvatus) in the Lower Kinabatangan, Sabah. Asian Primates. Vol. 4(1), 13-14.
Boonratana, R. 2000. Ranging behavior of proboscis monkeys (Nasalis larvatus) in the Lower Kinabatangan, Northern Borneo. International Journal of Primatology. Vol. 21, 497-518.
Burton, F. 1995. The Multimedia Guide to the Non-human Primates. Prentice-Hall Canada Inc.
Estes, R.D. 1991. The Behavior Guide to African Mammals. University of California Press.