LANGURS AND LEAF MONKEYS OF NORTHERN INDONESIA, BORNEO AND MALAYSIA

LANGURS

Hose's langurs

Langurs are mostly leaf-eating, tree-residing, forest-dwelling monkeys. They are regarded as among the most arboreal of all Old World monkeys. They are active throughout the tree canopy and can be found in both primary and secondary forests. They rarely come to the ground. When they do it is mainly to gain access to mineral sources.

Most langurs are grayish, brownish or blackish, with paler underparts. Some have light colored markings on their head or stripes on their thighs. Langur adults weigh from five to eight kilograms and have a head and body length of 42 to 61 centimeters (16.5 to 24 inches) and a tail length of 50 to 85 centimeters (20 to 33.5 inches) .

Langur bodies are adapted for tree life. They have long tails, a slender body, strong slender hands, and well developed fingers. Although langurs eat leaves the their primary sources of nutrition come from fruits and seeds. On a daily basis they range through the forest between 500 and 800 meters to forage.

The Colobinae subfamily of the Old World monkey family includes 61 species in 11 genera, including the black-and-white colobus of Africa, the large-nosed proboscis monkey of Borneo, and the gray langurs of South Asia India. Some classifications split the colobine monkeys into two tribes, while others split them into three groups. Both classifications put the three African genera Colobus, Piliocolobus, and Procolobus in one group. The various Asian genera are placed into another one or two groups. [Source: Wikipedia]

Websites and Resources: Animal Diversity Web animaldiversity.org ; BBC Earth bbcearth.com; A-Z-Animals.com a-z-animals.com; Live Science Animals livescience.com; Animal Info animalinfo.org ; World Wildlife Fund (WWF) worldwildlife.org the world’s largest independent conservation body; National Geographic National Geographic ; Endangered Animals (IUCN Red List of Threatened Species) iucnredlist.org

Presbytis Genus Langurs of Sumatra, Borneo, Java and Malaysia

Presbytis is a genus of Old World monkeys also known as langurs, leaf monkeys, or surilis native to Sumatra, Borneo, Java and smaller nearby islands in Indonesia and the the Thai-Malay Peninsula. They are smallish, slimly built primates. Their fur at the top is brown, grey, black, or orange, and at the lower surface whitish or greyish, sometimes also orange, with some species having fur designs at the head or at the hips. Their German name of Mützenlanguren ("capped langurs") comes from the hair on their head, which forms a tuft. Surilis range in adult length from 40 to 60 centimeters (with a 50- to 85-centimeter-long tail) and a weight of five to eight kilograms. [Source: Wikipedia]

Langurs of the Presbytis Genus differ from the other langurs: 1) in head shape (particularly the poorly developed or absent brow ridges, and the prominent nasal bones), 2) in the teeth, and 3) by the size of their small thumbs. Two other genera, Trachypithecus and Semnopithecus, were formerly considered subgenera of Presbytis. The species-level taxonomy of Presbytis is complex, and significant changes have been proposed for several in recent years.

Diurnal forest dwellers, Langurs of the Presbytis Genus mainly eat leaves, fruits, and seeds and spend nearly their entire lives in the trees. They live in groups of up to 21 animals (typically 10 or fewer animals in most species) consisting of a male, several females, and their young. A few species have been observed in monogamous pairs. Lone males and all-male groups have also been observed. The groups have a hierarchical arrangement, with intergroup communication that is both vocal and postural. Their gestation period is five to six 5–6 months, producing a single offspring. Newborns are white colored and have a black strip at the back, although some have a cross-shaped mark. By one year old, the young are weaned and at an age of 4–5 years, they are fully mature. The typical life expectancy in the wild remains poorly known for most species, but captive Sumatran surilis have lived more than 18 years.

Langur Species in Malaysia

Selangor Silvered Langurs (Trachypithecus selangorensis, Roos, Nadler, Walter, 2008) are gray monkeys. They live in peninsular Malaysia They are 40–76 centimeters (16–30 inches) long, with a 57–110 centimeter (22–43 inch) tail. They eat leaves, flowers, and fruit. They are a near-threatened species. Their numbers are unknown. Their population is declining.

Raffles' banded langurs (Presbytis femoralis, Martin, 1838) are gray in color. They live Singapore and southern Peninsular Malaysia. They are 42–61 centimeters (17–24 inches) long, with a 50–85 centimeter (20–33 inch) tail. They live in the forest and eat fruit, seeds, and leaves. They are critically endangered. 200–250 Their population is declining.

Robinson's banded langurs (Presbytis robinsoni, Thomas, 1910) are gray in color. They live in southern Malay Peninsula and are 42–61 centimeters (17–24 inches) long, with a 50–85 centimeter (20–33 tail. They live in the forest and eat fruit, seeds, and leaves. They are not threatened. Their numbers are unknown. Their population is declining.

Langurs on Borneo

Distribution of Selangor Silvered Langurs (red), Silvery lutungs (green), West Javan langurs (blue) and East Javan langurs (yellow)

Miller's langurs (Presbytis canicrus, G. S. Miller, 1934) are gray in color. They live in Eastern Borneo. They are 42–61 centimeters (17–24 inches) long, with a 50–85 centimeter (20–33 inch) tail. They live in the forest and eat fruit, seeds, and leaves. They are endangered. Their numbers are unknown. Their population is declining.

Hose's langurs (Presbytis hosei, Thomas, 1889) live on Borneo. They are 42–61 centimeters (17–24 inches) long, with a 50–85 centimeter (20–33 inch) tail. They live in the forest and eat leaves,, unripe fruits, seeds, flowers, bird eggs and nestlings. They are critically vulnerable. Their numbers are unknown. Their population is declining.

Maroon leaf monkeys (Presbytis rubicunda, S. Müller, 1838) are brown in color. There are five subspecies: 1) P. r. carimatae; 2) P. r. chrysea; 3) P. r. ignita; 4) P. r. rubicunda; and 5) P. r. rubida. They live on Borneo and are 42–61 centimeters (17–24 inches) long, with a 50–85 centimeter (20–33 inch) tail. They live in the forest and inland wetlands and eat leaves,, seeds, and fruit, as well as flowers and pith. They are critically vulnerable. Their numbers are unknown. Their population is declining.

White-fronted surili (Presbytis frontata, S. Müller, 1838) are brown in color. They live on Borneo. They are 42–61 centimeters (17–24 inches) long, with a 50–85 centimeter (20–33 inch)tail. They live in the forest and eat fruit, seeds, and leaves. They are critically vulnerable. Their numbers are unknown. Their population is declining.

Sabah grizzled langurs (Presbytis sabana, Thomas, 1893) live in Eastern Borneo. They are 42–61 centimeters (17–24 inches) long, with a 50–85 centimeter (20–33 tail. They live in the forest and eat fruit, seeds, and leaves. They are endangered. Their numbers are unknown. Their population is declining.

Sarawak surili (Presbytis chrysomelas, S. Müller, 1838) are gray and brown monkeys. There are two subspecies: 1) P. c. chrysomelas; and 2) P. c. cruciger. They live in northern Borneo. They are 42–61 centimeters (17–24 inches) long, with a 50–85 centimeter (20–33 tail. They live in the forest and eat fruit, seeds, and leaves. They are critically endangered. Their numbers are unknown. Their population is declining.

Dusky Leaf Monkeys

Dusky leaf monkeys (Trachypithecus obscurus) are found primarily on the Malay Peninsula, including southern Myanmar (Burma) and parts of Thailand. They also inhabit the islands of Langkawi, Penang, and Perhentian Besar in Malaysia. Their average lifespan in captivity is 25.0 years. Similar species have lived longer[Source: Lata Viswanathan, Animal Diversity Web (ADW) /=]

Also known as spectacled langurs or spectacled leaf monkeys, Dusky leaf monkeys range in weight from five to nine kilograms (11 to 20 pounds). Their head and body ranges from 42 to 61 centimeters (16.5 to 24 inches), with a tail that is between length from 50 to 85 centimeters (20 to 33.5 inches). Sexual Dimorphism (differences between males and females) is present: males tend to be slightly larger and heavier than females but there are no significant morphological differences between the two sexes. On average, an adult male weighs 7.4 kilograms, while adult females weigh approximately 6.5 kilograms. /=\

dusky leaf monkey mother and child

Dusky leaf monkeys are widely variable in color. According to Animal Diversity Web: Their upper parts may be any shade of brown, grey, or black, whereas the under parts, hind legs, and tail are paler. The face is grey and is often marked with a patch of white fur located around the eyes and mouth. Newly born dusky leaf monkeys are bright yellow or orange in color, and have a pink face; the fur changes to a greyish color within six months. The hands and feet are capable of grasping and closely resemble those of humans. The palms and soles are hairless and usually black. The fingers of dusky leaf monkeys are well developed, but are distinct because of their opposable thumb. The nonprehensile tail varies in length and fur coverage from short and hairless, to long and hairy. /=\

Dusky leaf monkeys can be found in a wide range of habitats but they have traditionally been forest dwellers and prefer dense forests with tall trees. They are primarily herbivores (primarily eat plants or plants parts), and folivores (eat mainly leaves). Their diet consists of young leaves, shoots, and seedlings. They feed from 87 different species of trees, ingesting both leaves and fruit. In general, a dusky leaf monkey eats up to two kilograms of food per day. In in captivity they eat sweet potato shoots, lettuce, cabbage, kangkong, grean beans, maize, carrots, and soft fruits. Meat was refused, but certain insects were occasionally accepted. /=\

On the International Union for Conservation of Nature (IUCN) Red List dusky leaf monkeys are listed as Near Threatened. In CITES (Convention on International Trade in Endangered Species of Wild) they are in Appendix II, which lists species not necessarily threatened with extinction now but that may become so unless trade is closely controlled. Dusky leaf monkeys are confined within a relatively small area of southeast Asia. It is probable that these forested areas are under threat of development or logging. Therefore, there is reason to believe that the species is threatened to some extent because of habitat loss, but there are no studies to support this. It is also seems plausible dusky leaf monkeys are hunted for food by humans. /=\

Dusky Leaf Monkey Behavior and Reproduction

Dusky leaf monkeys are arboreal (lives mainly in trees), scansorial (able to or good at climbing), diurnal (active during the daytime), motile (move around as opposed to being stationary), sedentary (remain in the same area), territorial (defend an area within the home range), colonial (living together in groups or in close proximity to each other), 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). The size of their range territory is 5000 to 12,000 square meters. Group territories between five and 12 hectares have been reported for animals inhabiting the Malay penninsula. /=\

Dusky leaf monkeys are very active during the day, but return to their roosts in the trees by night. In the tree canopy, they prefer to stay at heights of 35 meters or higher in trees. They move from tree to tree by climbing, leaping, and running quadripedally along branches. When feeding, dusky leaf monkeys pluck leaves and shoots off by hand. They also pull down leafy branches and browse on them directly. The motion of the tail plays a significant role in maintaining balance.

Dusky leaf monkeys are very social animals and travel in groups that consist of five to 20 individuals. Social groups usually have one or more adult males, and two or more adult females. The adult male has three main responsibilities, which include detecting predators, holding the group together, and patrolling the boundaries of the territories. Young monkeys play in groups near the vicinity of an adult female.

Dusky leaf monkeys have a wide range of calls that are considered to be quite complex. A variety of snorts, hoots, murmurs, and squeaks are used to communicate with other members of their social group. Details on communication in these monkeys are scant. However, we know that they use vocalizations to protect their territories from other members of the species. Like other primates, tactile communication (e.g. grooming, playing, mating, aggression) and visual communication (e.g. facial expressions and body postures) are probably both inmportant in these monkeys. /=\

Dusky leaf monkeys are polygynous (males having more than one female as a mate at one time). They engage in year-round breeding. Females have a menstual cycle lasting approximately three weeks. Oestrus is often accompanied by a swelling of the genitalia. The normal interbirth interval is about two years. Sexual maturity is reached between three and four years of age. The number of offspring is usually one. The average gestation period is 145 days. Births usually occur during the months of January, February, and March, but have been documented taking to during the summer months too.

Mitered Langurs

Mitrred langurs (Presbytis melalophos) are found in the rainforests of the Malay Peninsula, Sumatra, and western Borneo. They inhabit lowland and submontane dipterocarp and evergreen forests and areas on the margins of rivers. They prefer discontinuous understory at approximately 27 meters (90 feet) above the ground, but occasionally are found in the continuous main canopy and highest, emergent layers of the forest. Their average lifespan in captivity is 16 years. [Source: Dana Tedesco, Animal Diversity Web (ADW) /=]

The average weight of mitered langurs is six kilograms (13.2 pounds) and have long, bicolored tails. Sexual Dimorphism (differences between males and females) is present: Males are slightly larger than females. Like all members of the genus Presbytis, mitered leaf-monkeys have a short rostrum (hard, beak-like structures projecting out from the head or mouth) and weakly-developed brow ridges. They have long forelimbs and relatively long hindlimbs, which aid in their preferred means of locomotion, leaping and brachiation (swinging from tree limb to tree limb using their arms). Mitered leaf-monkeys are distinguished from other Presbytis species by their single-phrase call, fur characters, and skull features such as long nasals and narrow interorbitals. /=\

Mitered langurs have brownish-gray fur with the ventral side lighter than the dorsum. The tail is bicolored and the head has a distinct black crest. There are four subspecies of Mietred langur based on fur differences, distinctions in vocalizations, and geographic location: 1) P. m. bicolor is the whitest subspecies and 2) P. m. sumatrana is the darkest subspecies. The fur color of 3) P. m. mitrata and 4) P. m. sumatrana is intermediate. Neonates are white with a pale face and a dark, reddish-brown spinal stripe. /=\

Mitered langurs are frugivorous (fruit eating) and folivorous (leaf eating). Fruit comprises 50 to 60 percent of the diet; the rest consists of leaves and, occasionally, seed and flowers. The foregut is enlarged and has the capacity for microbial fermentation. Mitered langurs feed on up to 197 different tree species. It prefers new leaves to mature leaves.

On the International Union for Conservation of Nature (IUCN) Red List Mitered langurs are listed as Endangered. In CITES (Convention on International Trade in Endangered Species of Wild) they have no special status. Mitered langurs are mainly threatened vulnerable to habitat loss, especially due to logging and palm oil plantations. In areas where logging has occurred, groups have range more widely or fission into smaller subgroups to forage for food. After selective logging, groups often reoccupy forested territories. Habitat loss also occurs as a result of spreading agriculture and human development. /=\

Mitered Langur Behavior, Communication and Reproduction

Yellow-handed Mitered Langur (Presbytis melalophos melalophos), a subspecies of the Sumatran Surili

Mitered langurs are arboreal (lives mainly in trees), scansorial (able to or good at climbing), diurnal (active during the daytime), motile (move around as opposed to being stationary), sedentary (remain in the same area), territorial (defend an area within the home range) and social (associates with others of its species; forms social groups). They spend most of their time in the understory of the forest, leaping between small branch supports and are primarily active during the day. The size of their range territory is 14 to 30 hectares. Groups travel up to 950 meters in a day. There is usually an overlap of home ranges of a 20-30 percent when they occur but an overlap of 79 percent has been recorded. Habitat destruction has resulted in greater home range overlap and increased territoriality. [Source: Dana Tedesco, Animal Diversity Web (ADW) /=]

According to Animal Diversity Web: Mitered langurs live in groups consisting of one male and five to seven females. Groups with smaller home ranges are generally more territorial (defend an area within the home range), than groups with larger home ranges; territoriality is directly related to the supply of resources. Males identify the group's territory with vocalizations and displays. When groups approach each other, harem males will call to each other and may become physically agressive. Males may also be solitary or live in all-male bands. Solitary males are chased away from females by harem males and are generally confined to a resource-poor area of the forest. Females determine their group's movement and are responsible for encounters with another group. However, females remain uninvolved in intergroup conflicts. Females in a group show no evidence of a dominance hierarchy. /=\

Mitered langurs sense using vision, touch, sound and chemicals usually detected with smell. They communicate with vision and sound and employ choruses (joint displays, usually with sounds). Males announce their territory to other groups in the area with loud calls and distinct leaps. Males of neighboring groups call in chorus at intervals throughout the night. Males also call when two groups approach each other. These territorial calls are quite distinct from the alert calls sounded by a group member when a predator is spotted. Their main predators are birds of prey and , including the crested serpent eagle, and pythons. When a member of the group detects a predator, it issues an alert cry to other members of the group. The harem male attempts to distract the predator with loud cries and leaps, drawing the predator away from the rest of the group by as much as 73 meters (240 feet).

Mitered langurs are polygynous (males having more than one female as a mate at one time). They engage in year-round breeding and live in single-male groups with five to seventeen females. The single male of the group mates with females in the group. Females exhibit no external sign of estrus and solicit copulation. General reproductive behavior has not been studied in Mitered langur. In other colobines, males reach maturity at 34-47 months and females reach maturity at 35-60 months. Gestation period is 155-226 days. Most colobines that have been studied breed throughout the year, with 16-25 month interbirth intervals. In Presbytis thomasi, a close relative of Mitered langur, females give birth to one offspring per interval. The young are weaned at 12-15 months. In many colobines, infants are transferred between the mother and other group females; however, this behavior has not been observed in the mitered langur. Females nurse and care for their young until they become independent. Immature males disperse from their natal group when they are half-grown, while females remain in their natal group. The role of male mitered langurs is unclear in raising young./=\

Silvery Lutungs

silvery lutung

Silvery lutungs (Trachypithecus cristatus) are found throughout southern Southeast Asia and Indonesia — including in the Malayan Peninsula, Borneo, Sumatra, Java, Thailand, and the Natuna Islands. They are known by different common names in different countries. In English, they are referred to as silvered leaf monkeys, whereas in India they are referred to as silvered langurs. In their endemic area of Malaya, they are called lutong. One subspecies, T. c. vigilans, is found only on the Natuna Islands. The other subspecies, T. c. cristatus, is found in all areas to which the species is endemic. The lifespan of these monkey in captivity has been up to 29 years. It is estimated that their average lifespan in the wild is 20 years.[Source: Christine Bedore, Animal Diversity Web (ADW) /=]

First described by Sir Thomas Stamford Raffles in 1821, silvery lutungs live in tropical areas in forests, rainforests, scrub forests, wetlands, swamps and agricultural areas. Their habitat is similar to that of other members of its subfamily Colobinae but their habitat varies somewhat depending on the region. On the Malaysian Peninsula they live mangrove and sub-coastal forests whereas on Java and Sumatra they live in the trees of inland forests. They have also been found in bamboo forests, on plantations, and in swamp forests. They rarely leave the trees. When they occasionally do come down to the ground, they do so quickly and retreat to the trees if they sense a threat.

Silvery lutungs are not endangered. On the International Union for Conservation of Nature (IUCN) Red List they are listed as Near Threatened. In CITES (Convention on International Trade in Endangered Species of Wild) they are in Appendix II, which lists species not necessarily threatened with extinction now but that may become so unless trade is closely controlled. Their main threatened is habitat destruction of the forests where they live for agriculture. Among the natural predators of silvery lutungs are snakes, tigers, leapords, and jackals.

Silvery Lutung Characteristics and Feeding

Silvery lutungs range in weight from 4.9 to 8.0 kilograms (10.8 to 17.6 pounds). Their head and body length ranges from 46.5 to 56 centimeters (18.3 to 22 inches). Sexual Dimorphism (differences between males and females) is present:The sexes look alike but males are larger, with the average weight of males being 7.1 kilograms and females being 6.2 kilograms. The head and body length of males ranges from 52.4 to 56 centimeters, whereas that of females is typically 46.5 to 49.6 centimeters. Both sexes have a tail that is longer than their body; tail length ranges from 63 centimeters to 84 centimeters. Newborns are about 20 centimeters and 0.4 kilograms at birth. They reach their adult size at about five years of age. [Source:Christine Bedore, Animal Diversity Web (ADW) /=]

Christine Bedore wrote in Animal Diversity Web: Silvery lutungs get their name from the coloring of their fur. There is some variation in the color of their fur, including brown, gray, brownish-gray, or black. No matter what the color, some hairs are gray-white and give a silver appearance. Polymorphisms are very rare; the best known is a red morph that exists in Borneo. The hands and feet are prehensile, hairless, and usually black in color. Males and females are difficult to distinguish from one another. The only visible difference is irregular white patching on the inside of the flanks of females. Males are also slightly larger than females: females are 89 percent of the body weight of the males. Newborns have orange fur and white colored hands, feet, and face. The skin changes color within days of birth to black, as in the adults of this species. The orange fur changes to the adult color within three to five months. /=\

Silvery lutungs, as their name suggests are folivores (eat mainly leaves). They are also classified as herbivores (primarily eat plants or plants parts). Among the plant foods they eat are fruit, seeds, shoots, flowers, and buds. Some adaptations have been made to increase efficiency of digesting and processing plant materials. The teeth have pointed cusps on their two transverse ridges, and are referred to as bilophodont. The stomach has become sacculated and contains bacteria for fermentation of the plants. The stomach is also enlarged to hold a large amount of food, given that the food they eat is nutritionally poor. They also contain large salivary glands that act to neutralize stomach acid that may cause damage if seepage from the stomach occurs. /=\

Silvery Lutung Behavior and Communication

Silvery lutungs are arboreal (lives mainly in trees), scansorial (able to or good at climbing), diurnal (active during the daytime), motile (move around as opposed to being stationary), nomadic (move from place to place, generally within a well-defined range), sedentary (remain in the same area), territorial (defend an area within the home range) and social (associates with others of its species; forms social groups). They travel about 200 to 500 meters throughout their territory daily. The male of the group leads the females while guiding them with vocalizations. The territory a group occupies averages 43 hectares. [Source: Christine Bedore, Animal Diversity Web (ADW) /=]

According to Animal Diversity Web: The behavior of silvery lutung is not well known. Like many primates, silvery lutung is a social species. Individuals form groups consisting of one male and nine to 48 females, depending on the location. Juveniles usually disperse from their natal group at maturity. Silvery lutung is a very shy species. Individuals are occasionally seen in the vicinity of human settlements, but retreat quickly if they feel threatened. /=\

Silvery lutung travels primarily via brachiation (swinging from tree limb to tree limb using their arms), although individuals may walk on the ground when traveling with the group. They show a low level of aggression within the social group. Sociosexual, gestural, and vocal interactions are the common features of the social relationships of these monkeys. This may be due to the abundance of food in their habitat and their feeding behavior of facing toward the tree while eating. These both decrease the frequency of interaction with other members of the group, resulting in less need for tight group cooperation. /=\

Although the species is fairly peaceful, there is occasionally conflict with neighboring groups of the same species over territory. Many times, the groups will live in peace with each other in close proximity after the initial conflict. There is some aggression within groups, and this may be related to sex. Generally, there are only intraspecific conflicts. Silvery lutung tends to co-exist comfortably with other species such crab-eating macaquesthat inhabit the same regions. /=\

Silvery lutung communicate with vision, touch, sound and chemicals usually detected by smelling and sense using vision, touch and chemicals usually detected with smell. They are the most silent of the colobine species. Researchers describe them as being grave, serious, expressionless, and slow moving. They make 13 different vocalizations, which are most common at dusk and dawn. They vocalize to signal conflict, fear, warnings, alarms, and salutation. In addition to these vocalizations, males make threatening calls and young call for their mothers. Although members of the species are relatively quiet, individuals also communicate nonvocally with each other in social play, grooming, and light fighting. /=\

Silvery Lutung Reproduction and Offspring

Silvery lutungs are polygynous (males having more than one female as a mate at one time). They are also cooperative breeders (helpers provide assistance in raising young that are not their own). They typically breed once every year. Breeding does not appear to be strictly limited by season although there are more births from December to May when food is more abundant. The average number of offspring is one. The estrous cycle is 24 days. Females reach sexual maturity at four years of age, whereas males mature between four and five years of age. /=\

Groups of Silvery lutung are generally one-male groups in which one male defends and mates with multiple females. All-male groups as well as single males are also found. Occasionally, a male from an all-male unit or an individual male will challenge the male of a male/female group. If the challenger presides over the defending male, infanticide usually occurs. Females commonly care for young of other mothers in the group, and often even allow other young to nurse.

The average gestation period is six months. Mothers nurse their young for months after birth. Females, as well as males, teach their young, play with them, and protect them from danger. However, typically infants approach males to be carried and to play. Young are well developed when born. Their eyes are open and their forearms are strong, allowing them to cling to the mother. /=\

Mystery Monkey — Silvery-Lutung-Proboscis-Monkey Hybrid

A "mystery monkey" spotted in Borneo turned out to be a cross between a proboscis monkey — famous for its oversized nose — and a silvery lutung (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.

Image Sources: Wikimedia Commons

Text Sources: Animal Diversity Web animaldiversity.org ; National Geographic, Live Science, Natural History magazine, David Attenborough books, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Discover magazine, The New Yorker, Time, Reuters, Associated Press, AFP, Lonely Planet Guides, Wikipedia, The Guardian, Top Secret Animal Attack Files website and various books and other publications.

Last updated December 2024