PROBOSCIS MONKEYS
Proboscis monkeys (Scientific Name: Nasalis larvatus) are named for their long bulbous noses. Native to the rivers, swamps and coastal lowlands of Borneo in Malaysia, Brunei and Indonesia, they prefer coastal regions to inland areas and inhabit mangrove forests along rivers and estuaries, swamp-land, and lowland rainforests. Indonesians call them "Belanda," which means "white man."[Source: Tim Laman, National Geographic, August 2002]
About 8,000 proboscis monkeys are estimated o be living in the wild. They need relatively large areas to live in to collected all the food need. Proboscis monkeys have had their numbers reduced by poaching and loss of habitat resulting from clearing of the rain forest. Particularly damaging for them has been the drainage of swamps and shrimp farming in coastal habitats.
Proboscis monkeys are one of Asia’s largest monkeys. Adult males can reach lengths of two feet, excluding their tail, and weigh 50 pounds. Females are about half the size. They have long tails which are not used for gripping but may provide balance when then the monkeys fly through the air. They also have very long limbs, ideal for swinging in branches and moving from tree to tree. Infants have dark fur and bluish faces. Twins are rare.
Only their lifespan in captivity is known. The record is 23 years. Their average lifespan in captivity is 13.6 years. [Source: Max Planck Institute for Demographic Research]
Proboscis monkeys are great leapers. They can leap great distances from one branch to branch and tree to tree. They push off with their powerful hind legs and fly through the air with their arms extended over their heads, ready to grasp a branch. Mothers leap with their offspring clinging to their stomachs.
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Studies by Elizabeth Bennett and Carey Yeager
Proboscis Monkey Characteristics
Males have the largest noses. They are long, bulbous and drop downward below the chin. When males grunt their nose jerk upwards. Female noses are significantly smaller and turned up and look like the noses on clowns. Youngsters have short, turned-up button nose. The large male noses are believed to be help them attract females and possible dissipate excess heat.
Proboscis monkeys range in weight from seven to 22 kilograms (15.42 to 48.46 pounds) and range in length from 60 to 70 centimeters (23.62 to 27.56 inches). There is webbing between their digits which allow they to swimming. They are endothermic (use their metabolism to generate heat and regulate body temperature independent of the temperatures around them), homoiothermic (warm-blooded, having a constant body temperature, usually higher than the temperature of their surroundings) and have bilateral symmetry (both sides of the animal are the same). [Source: Amy Woltanski, Animal Diversity Web (ADW) /=]
Proboscis monkeys They are sexually dimorphic. Sexual Dimorphism (differences between males and females): Males are larger than females. Sexes are colored or patterned differently with the male being more colorful. Ornamentation is different. /=\, with males having an average length of 70 centimeters and weight of between 16 and 22 kilograms. Females have an average length of 60 centimeters and weigh between seven and 12 kilograms. Males have a large protruding nose, which enhances vocalizations through resonance. The nose of the female is smaller.
The fur of the adult proboscis monkey is pink and brown with red around the head and shoulders. The arms, legs, and tail are gray. Males have a black scrotum and a red penis. Infants are born with a blue colored face that at 2.5 months darkens to gray. By 8.5 months of age, the face has become cream colored as in the adults.
Proboscis Monkey Feeding Habits
Proboscis monkeys have chamber stomachs like ruminants such as cows. They eat large quantities of leaves and rely on bacteria in their stomachs to break down the cellulose in the leaves. These monkeys often spend several hours eating and several hours relaxing while food in their stomachs digests.
Proboscis monkeys are herbivores (eat plants or plants parts), folivores (eat leaves) and frugivores (eat fruits). They prefer fruits, seeds, young leaves, and shoots of mangrove plants. They may also eat some invertebrates such as caterpillars and larvae. They are more frugivorous from January through May and more folivorous (leaf-eating) from June through December. [Source: Amy Woltanski, Animal Diversity Web (ADW) /=]
Proboscis monkeys have a permanent pot belly, which encloses a large chambered stomach necessary to process all the fibrous food they eat. They avoid sweet fruits which could cause deadly bloating from rapid fermentation. Male proboscis monkeys sometimes move their noses out of the way when they eat.
Proboscis Monkey Swimming
Proboscis monkeys are regarded as the best swimmers among primates . They have partly webbed hands and feet, which helps them swim and may help them walk better on mud. They have been observed swimming on the surface and underwater and making their across large rivers. Proboscis monkeys will leap out of the trees into the water. They are capable of swimming 20 meters underwater. They may cross rivers by swimming if alone or they may cross by jumping from a tree on one bank to one on the other side at narrow points if in a group.
One male proboscis monkeys described in National Geographic crossed a 400-foot-wide river by climbing a 30-meter-high tree and, with a running start, leapt as far as he could, hitting the water with a huge belly flop, and almost knocking himself out in the process. He then swam quickly to the shore. Once a group of proboscis monkeys observed leaping in unison from 15-meter-high trees into the water. The strategy is thought to be a way of staying clear of crocodiles.
Proboscis monkeys don’t have a very good sense of direction. Once a fisherman fished one out of the water that was swimming toward China 500 miles away. They also miss their marks. They are Sometimes end up swimming when they attempt to leap from one tree to another and fall short, into the water.
Proboscis Monkey Behavior and Communication
Proboscis monkeys are arboreal (lives mainly in trees), diurnal (active during the daytime), motile (move around as opposed to being stationary), sedentary (remain in the same area), social (associates with others of its species; forms social groups), and have dominance hierarchies (ranking systems or pecking orders among members of a long-term social group, where dominance status affects access to resources or mates). [Source: Amy Woltanski, Animal Diversity Web (ADW) /=]
Proboscis monkeys are most active from late afternoon until dark and generally are never more than 600 meters from a river. When moving through the trees, they are quadrupedal (use all four limbs). They are relatively unafraid of humans due their contract with researchers. This is good for tourists who can get close without upsetting them.
Proboscis monkeys groups generally live in a territory that covers about two square kilometers and stay within 400 meters of a river. They spend most of the day foraging for food. At night they gather in the upper canopy of tree along the edge of rivers to sleep. It is unclear why they sleep near rivers. Sometimes different groups sleep relatively close to one another, an unusual habit among monkeys.
Proboscis monkeys communicate with vision, touch and sound and sense using vision, touch, sound and chemicals usually detected with smell. They make several sounds for communication. Growls are made by males and are used to calm the group members. Honks are made by males as a threat or to warn of predators. Shrieks are made by females and both sexes of juveniles to show agitation or excitement, and screams are given during agonistic encounters. Social grooming is performed, usually between females. The grooming usually last 1 to five minutes and is performed by both individuals.
Proboscis Monkey Group Behavior
According to Animal Diversity Web: There are two types of groups within the proboscis monkey society: unimale and all-male. These groups number three to 32 individuals. Several of the groups will come together in the evening to sleep. These multigroup gatherings are called bands. Proboscis monkeys sleep zero to 15 meters from the river's edge. They do not sleep in the same place on consecutive nights. The same groups associate regularly and there is little aggression between males in unimale groups. Adult males coordinate the group's movements and lead the group. Females do not leave their natal group. Males disperse at 18 months of age.
Proboscis monkeys live in groups of 10 to 30 members. They have highly organized social structures. Harem groups, with one male and several females and their offspring, are the basic social units. Males, who are usually kicked out of the group at an early age, form all-male groups that hang out together until they are mature enough to challenge other males and form their own harem groups.
Females generally get along well but they do bicker and squabble over choice sleeping and feeding spots. They often chose the feeding spots and males follow them. Although young proboscis stay pretty close to their mothers, females shar in infant care. Mothers may pass their infants off to one another or older siblings.
Proboscis Monkey Mating, Reproduction and Offspring
Proboscis monkeys are polygynous (males having more than one female as a mate at one time). The basic social unit in proboscis monkeys is a single adult male with from two to seven adult females. The males mate with females in their social group. [Source: Amy Woltanski, Animal Diversity Web (ADW) /=]
There seems to be no single breeding season with breeding taking place from February to November. Male proboscis monkeys try to scare off rivals with bellowing roars and honks. If that doesn’t work they will jump around aggressively shaking trees and branches. Rarely do they actually fight. Copulation is initiated by the female through pursing of the lips, shaking of the head from side to side, and presentation of the hindquarters to the male. Females will continue to initiate copulations even after they have conceived.
Usually a single young is born after a 166 day gestation period. Births usually occur at night. The female sits on a tree branch during the birth. After the infant is born, the mother consumes the placenta. Young proboscis monkeys have dark hair and a bluish face when they are infants. Families often take turns and help each other take care of their offspring. Infants stay close to their mothers for about one year.
Females can produce offspring each year. The age in which they are weaned ranges to seven months and the average time to independence is 12 months. On average females reach sexual or reproductive maturity at around four years of age. On average males reach sexual or reproductive maturity at seven years.
As is the case for most primates, newborn proboscis monkeys are fairly helpless. They must be carried by their mother until they are able to walk on their own. Mothers provide their offspring with milk. They also keep their infants clean through grooming. The role of the male in parental care is less direct. Although males do not care for infants the way females do, it can be argued that they provide important protection for the young by excluding potentially infanticidal rival males from the group. /=\
Proboscis Monkey Threats and Conservation
Known predators of proboscis monkeys includes leopards and crocodiles. The anti-predator behavior of these monkeys has not been described in detail. Adult males sometimes make sounds that seem to be meant to scare off potential predators. [Source: Amy Woltanski, Animal Diversity Web (ADW) /=]
Proboscis monkeys are considered a delicacy among some people although they are not heavily hunted. They are also desired for zoos because of their unique appearance. They are protected from hunting and capture in Borneo but the destruction of the mangrove forest has limited the population.
Proboscis monkeys are listed in Appendix I by the Convention on International Trade in Endangered Species (CITES). Appendix I species are defined as a species threatened with extinction with trade allowed only in extreme circumstances. They are listed as endangered by the International Trade in Endangered Species of Wild Fauna and Flora (IUCN). 'Endangered' is defined as an estimated 50 percent reduction in the population in the next 10 years.
Mystery Monkey — Silvery-Langur-Proboscis-Monkey Hybrid
A "mystery monkey" spotted in Borneo turned out to be a cross between a proboscis monkey and a silvery langur (Silvered leaf monkey). The hybrid was particularly rare because it came from two distantly related species that aren't in the same genus. Competition for forest space may be behind the unlikely mix, with shrinking habitats driving male proboscis monkeys to take over langur groups. Hybrids are usually infertile, but researchers noted that the proboscis-langur cross appeared to be nursing an infant. [Source: Patrick Pester, Live Science, October 25, 2023]
A study on the mystery monkey was published in the International Journal of Primatology. Business Insider reported: The mysterious primate spotted near the Kinabatangan River in Malaysian Borneo, is likely to be the offspring of a proboscis monkey and a silvery langur — two species that inhabit the same forest and are distantly related, researchers said. [Source: Alia Shoaib, Business Insider May 8, 2022]
While closely related species occasionally interbreed to create hybrids, hybridization between distantly related species is "rarely observed in the wild," according to the study. The two monkey species do not even belong to the same genus and visually look very different from each other. Adult proboscis monkeys have reddish-brown fur and elongated noses, while adult silvery langurs have gray-tipped dark fur and flatter faces.
The mysterious primate was first seen by researchers in photos on social media in 2017, while it was still a baby. Photos from 2020 suggest that the monkey is now a grown female and has a baby of her own. "She appeared to be nursing a baby," study co-author Nadine Ruppert, a primatologist at the University of Science Malaysia, told Live Science. "We were all in awe. It was quite surreal."
Most hybrids born from different species are sterile and unable to produce offspring, according to Live Science, which adds to the mystery of this monkey and her baby. While it's possible she was taking care of another female's baby, she appeared to have swollen breasts, suggesting she was lactating. Ruppert told Newsweek that the existence of the unusual hybrid could be evidence of an ecosystem out of balance. "Seeing this putative hybrid is per southeast not of concern to the balance of the ecosystem or the two species, however, it is an alarming symptom of an ecosystem that already seems out of balance," she said.
The males of both species typically disperse from their families once they mature to find mating opportunities. However, habitat decline due to deforestation is limiting mating opportunities for these species, which could explain how the hybrid came to be, Ruppert told Newsweek.
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Last updated December 2024