Rhinopithecus avunculus

Geographic Range

Tonkin snub-nosed monkeys are found in subtropical areas of Vietnam with evergreen forests. These areas are typically associated with karst limestone hills and mountains. Populations have been confirmed in the past in seven provinces of Northern Vietnam: Ha Giang, Tuyen Quang, Cao Bang, Yen Bai, Bac Kan, Thai Nguyen, and Quang Ninh. They have been found recently in Ha Giang, Tuyen Quang, and Bac Kan Provinces, and possibly in Thai Nguyen Province.

• Biogeographic Regions
• oriental oriental
  • native native

Habitat

Tonkin snub-nosed monkeys only occur in subtropical broad-leaf and bamboo forests that have monsoon rainfall and tropical temperatures. These forests are usually found on top of limestone hills at elevations of less than 1000 m above sea level. Tonkin snub-nosed monkeys are the only snub-nosed monkeys that occur in subtropical areas.

• Habitat Regions
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• rainforest rainforest

Physical Description

Both sexes of adult Tonkin snub-nosed monkeys have upturned noses. They also have fairly slender bodies with slender digits on the hands and feet in comparison to other species in the genus Rhinopithecus . Coat color and pattern variation has been reported among populations and individuals. The general pattern is black fur on the outer limbs and back, the dorsal surface of the tail, and the hands and feet. The elbows, chest, ventral side of the tail, inside surfaces of the limbs and parts of the face are creamy-white. Parts of the face are hairless, particularly around the nose and eyes, and have pale blue skin. They also have orange coloration on the throat and dark coloration that outlines the mouth. Males and females differ slightly in coloration. Males show more pronounced orange around the throat and darker black around the mouth. In juveniles, the black parts of the fur appear gray, they lack the orange in the throat region, and the black around the mouth is not as pronounced as it is in adults. The average mass of males is 13.8 kg and the average mass of females is 8.3 kg. The length from the top of the head to the end of the body ranges from 51 cm and 65 cm, and the length of the tail ranges from 66 to 92 cm. Dental formula in the genus Rhinopithecus is I 2/2, C 1/1, P 2/2, M 3/3, for a total of 32 teeth. There is also sexual dimorphism in terms of canine size, with males having larger canines on both top and bottom jaw.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger
• sexes colored or patterned differently

Reproduction

The social structure Tonkin snub-nosed monkeys has been described as being one male monkey with multiple females and juveniles or groups of all males, suggesting a polygynous mating system. A female will engage the male by getting him to follow her to various branches; she will then move her tail above and to one side of her body prior to male mounting. Once the male has positioned his feet on the branch he will mount the female from the rear initiating copulation which was reported to have lasted approximately 43 seconds. In one case, after copulation the female moved to a neighboring tree and the male moved to a lower branch where he moved his forelimb in front to of his face and briefly shook his head. This description is the only observed mating event in Tonkin snub-nosed monkeys.

• Mating System
• polygynous polygynous

There has been little research on the reproductive behavior of these monkeys as they are rare and difficult to observe. After a gestation period of about 200 days, females give birth to 1 or 2 offspring in the spring or summer. Males become sexually mature at about 7 years of age and females at about 4 years of age. There is nothing reported about the lactation period of this species.

• Key Reproductive Features
• iteroparous iteroparous
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• viviparous viviparous

There is not much known about the level of parental care exhibited by this species of snub-nosed monkey . Adult females allogroom other members of the group. Allo-parental care has been observed in golden and black snub-nosed monkeys, ( Rhinopithecus roxellana and Rhinopithecus bieti ) respectively, so it is possibly an alement of social behavior in Tonkin snub-nosed monkeys also. It is likely that females invest heavily in young, as this is typical of other species in this group.

• Parental Investment
• female parental care female parental care
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female
• pre-independence
  • protecting
    • female
• post-independence association with parents

Lifespan/Longevity

The typical lifespan in colobine monkeys is about 20 years, with a lifespan of about 29 years in captivity. Lifespans of Tonkin snub-nosed monkeys are not reported.

Behavior

Tonkin snub-nosed monkeys typically organize themselves into either all male groups or groups of a single male with multiple females and juveniles; these groups typically feed, sleep, and travel together. These monkeys are diurnal and sleeping sites for this species are usually on lower branches of trees near steep mountain sides so as to be protected from cold winds at night. Groups sometimes split into separate groups or some groups come together to form a larger group; this group fission-fusion suggests that there is inter-group tolerance. Because groups fragment at times and fuse with other groups at other times, this species does not appear to be territorial. Females allogroom other members of the group. The type of locomotion used to move between trees is almost always by quadrupedal walking, but they also use climbing and leaping. Other types of behavior associated with adult movement being leaping between trees, hanging from the branches, and occasional brachiation.

• Key Behaviors
• arboreal arboreal
• scansorial
• diurnal diurnal
• motile motile
• sedentary sedentary
• social social

Home Range

Home range size is not reported for Tonkin snub-nosed monkeys. Some observations suggest that they will spend most of their time within a range of roughly 10 square kilometers.

Communication and Perception

Vocalizations are the primary means of communication. The main vocalization of this species sounds a lot like a hiccup (“huu chhhk”) and is used either in alarm calls or to communicate with other individuals. This kind of communication usually occurs during traveling or when locating a resource. Alarm calls are usually done in the presence of researchers. These monkeys, like other primates, probably perceive the world well with binocular, color vision and use pheromones to communicate with other members of this species, but there has been no research on communication and perception in Tonkin snub-nosed monkeys.

• Communication Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Tonkin snub-nosed monkeys eat leaves from trees, mainly bamboo or other evergreen leaves. They are not strictly folivorous, as they eat a variety of plant parts and fruits as well. The diet is comprised of 28% leaf stems, 28% fruits, 11% young leaves, 22% unripe fruit, 8% flowers, and 3% seeds. Thirty-one food species have been identified belonging to 21 families make up the diet of the Tonkin sub-nosed monkey. The plant species Iodes seguini , Garcinia fagraeoides , Acer tonkinensis , Excentrodendron tonkinensis , and Brassaiopsis stellate are consumed the most. They have a specialized digestive system that is adapted for the digestion of leaves, including a sacculated stomach. Their strong jaw musculature is related to their dietary preferences for tough plant foods.

• Primary Diet
• herbivore herbivore
  • folivore folivore
  • frugivore frugivore

• Plant Foods
• leaves
• wood, bark, or stems
• seeds, grains, and nuts
• fruit
• flowers

Predation

Humans have been known to hunt and eat Tonkin snub-nosed monkeys despite the meat’s apparently bad taste. No other predators of Tonkin snub-nosed monkeys are known, but it is likely that they are preyed on by arboreal snakes and large birds of prey as well as forest cats.

Ecosystem Roles

It is unclear what role these animals play in the ecosystem as they are rare. Tonkin snub-nosed monkeys are herbivores so they may impact vegetation in their habitat. Since they eat fruits, they could aid in the dispersal of seeds.

• Ecosystem Impact
• disperses seeds

Economic Importance for Humans: Positive

Tonkin snub-nosed monkeys have been used by locals as a food source and also to for traditional "medicines," which have no true medicinal value. It is reported that body parts are sometimes traded the borders of Vietnam and China. The hunting of this species for these purposes poses one of the biggest threats to its conservation and has therefore been made illegal.

• Positive Impacts
• food food
• body parts are source of valuable material

Economic Importance for Humans: Negative

Tonkin snub-nosed monkeys do not negatively impact humans.

Conservation Status

Tonkin snub-nosed monkeys are critically endangered and completely restricted to northern Vietnam. The biggest threats to this species are hunting and habitat degradation caused by humans. Humans hunt and trap these monkeys for food, medicine and trade. All of these acts are deemed illegal but still occurs. Habitat destruction is also causing a decline in the population of the species. People who live in these areas harvest bamboo and cut down trees to harvest the wood and fruit. Gold mining in the area has also destroyed parts of the habitat by clearing and excavating the land. Tonkin snub-nosed monkeys have been recognized as one of the world’s 25 most endangered primates since 2000 and were ranked as number 8 in the 2006 to 2008 report. A survey in 2006 estimated the total population for the entire species was about 150 individuals, but it is possible that it is lower.

Additional Links

Encyclopedia of Life

Contributors

Rachel Cherka (author), University of Manitoba, Jane Waterman (editor), University of Manitoba, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

Boonratana, R., X. Le. 1998. Conservation of Tonkin Snub-nosed Monkeys (Rhinopithecus [Presbyticus] avunculus) in Vietnam. Pp. 315-322 in The Natural History of the Doucs and Snub-nosed Monkeys . Singapore: World Scientific Publishing Co. Ltd..

Boonratana, R., X. Le. 1998. Preliminary Observations on the Ecology and Behaviour of the Tonkin Snub-nosed Monkey (Rhinopithecus [Presbyticus] avunculus) in Northern Vietnam. Pp. 207-215 in The Natural History of the Doucs and Snub-nosed Monkeys . Singapore: World Scientific Publishing Co. Ltd..

Covert, H., L. Quyet, B. Wright. 2008. On the Brink of Extinction: Research for the Conservation of the Tonkin Snub-nosed Monkey (Rhinopithecus avunculus). Pp. 409-427 in Elwyn Simons: A Search for Origins . New York: Springer Science and Business Media, LLC.

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A Conservation Action Plan for the Tonkin Snub-nosed Monkey in Vietnam

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