Tonkin Snub-Nosed Monkey, Rhinopithecus avunculus
TONKIN SNUB-NOSED MONKEY
Rhinopithecus avunculus
Geographic Distribution and Habitat
The Tonkin snub-nosed monkey (Rhinopithecus avunculus) is endemic to Vietnam, which means that it is found nowhere else on Earth. As some of the rarest and most endangered primates in the world, there are only a few subpopulations of the monkeys remaining, residing in Vietnam’s Ha Giang and Tuyen Quang Provinces, east of the Red River.
They make their homes in the tropical evergreen forests among Vietnam’s karst limestone hills and mountains. Karst is a unique topographic feature that is shaped by the erosion of limestone, resulting in a landscape of caves, underground streams, sinkholes, and large rock formations that can resemble stone trees or pillars. Tonkin snub-nosed monkeys live at elevations between 650 to 4,600 feet (200 and 1,400 m) above sea level.
Tonkin snub-nosed monkeys were formerly classified in the genus Pygathrix, with the douc langurs. They have since been moved to their current genus, Rhinopithecus, with the three other species of snub-nosed monkeys. The genus is aptly named, as the prefix “rhino-” means “of the nose”, and the members of the genus are known for their interesting noses!
Size, Weight, and Lifespan
Tonkin snub-nosed monkeys are the largest primates in Vietnam and the smallest species of their genus, the other members of which all live in China. They measure 20 to 24 inches (51-62 cm) from their head to the base of their tail. Their tail adds another 26 to 36 inches (66-92 cm) to their overall length. Males are considerably larger than females, averaging 31 lbs (14 kg) compared to the females’ 19 lbs (8.5 kg). Though data on their lifespan is not available, based on closely related species, they likely live into their late teens and twenties.
Appearance
The most striking feature of a Tonkin snub-nosed monkey is undoubtedly its face. The bright colors make the monkeys look a bit like they’re donning some hastily-applied clown makeup. Their eyes are framed in powder blue and they have a dark blue-gray triangle around their nose beneath their eyes. Their lips are puffy and pink, like a clown’s big red lips. Their nose is dainty and so upturned that it looks a bit skeletal– truly the other end of the spectrum from a fellow Afro-Eurasian primate, the proboscis monkey (Nasalis larvatus). Their bodies are mostly slate gray or black, with their bellies, inner arms, and inner legs a creamy white. They also have a prominent orange patch on their throat. Their tail is extremely long and covered in a mix of black and white fur, except for the tip which is pure white. Their fingers and toes are longer and more slender than the other members of their genus. They exhibit subtle sexual dimorphism– that is, visual differences between males and females– as the males are larger and have a more apparent orange throat patch than females. Infants look similar to their parents, though their back is more gray than black and they do not have an orange throat patch.
Diet
Tonkin snub-nosed monkeys eat a wide variety of foods, including both young and mature leaves, ripe and unripe fruits, flowers, and seeds. Like other colobine monkeys, those in the subfamily Colobinae, they possess a sacculated stomach in which food is fermented with bacteria. This allows them to digest mature leaves which other primates often have a difficult time digesting.
Behavior and Lifestyle
Tonkin snub-nosed monkeys are diurnal, which means that they are awake during the day and sleep at night. They are primarily arboreal, meaning that they spend nearly all their time in the trees. Although they usually spend the day high in the canopy, at night, they sleep in trees rather low to the ground. They tend to pick sleeping trees that protect them from the strong, cold mountain winds. They move about quadrupedally—on all fours—though occasionally they may hang under a branch from their arms in what’s known as a suspensory posture. The monkeys are known to be shy: researchers have observed that while they do not flee immediately upon spotting humans, they usually do shortly thereafter.
Though they were first identified in 1912, Tonkin snub-nosed monkeys number so few that they were later thought to be extinct by the scientific community. It wasn’t until the 1990s that they were “rediscovered” to the wider world.
Tonkin snub-nosed monkeys live in groups of up to 30 individuals, though 12-15 is more common. For this reason, they are an oddity within their genus, as the other three snub-nosed monkey species all collect into huge troops of up to 500 members, among the largest primate groups in the world. Because of this, some experts speculate that the Tonkin snub-nosed monkey’s relatively small group size is a reflection of their small and fragmented population, and would be larger if the species was doing better. A group’s home range is estimated to be about 940 to 1,400 acres (380-560 ha). Groups are composed of one adult male, several adult females, and their offspring. The groups usually come together as one to sleep and to feed, and may otherwise spread out. Occasionally, multiple groups may join together, though it is not clear what prompts this behavior. All-male bachelor groups also form, usually consisting of two to three adult males and several more juvenile males. These groups form as males mature and leave the groups they were born into—their natal groups—before finding mates and forming their own groups. Bachelor groups often join up with mixed-sex groups at sleeping sites and feeding trees, suggesting a lack of territoriality among the groups.
Allogrooming is an important behavior that Tonkin snub-nosed monkeys engage in regularly. Allogrooming is the grooming of another groupmate. It serves the practical purpose of removing parasites and debris but is also very important for group bonding. One study recorded that a group spent about 10% of their time grooming, about 70% of which was allogrooming (the remaining 30% was self-grooming). In all observations of allogrooming, in which troop members groom one another, it was an adult female grooming either a juvenile or another adult. Play is also an important behavior for young monkeys. It is not only a form of bonding, but it can help to develop muscles, coordination, and skills in the young.
One documented vocalization used by Tonkin snub-nosed monkeys has been described as a hiccup-like “huu chhk”. This sound was used as an alarm call when the monkeys were surprised by human researchers. It may also be used as a contact call, which helps to keep the monkeys near their group as they spread out to forage. At least two snub-nosed monkey species, the gray snub-nosed monkey (R. brelichi), and the golden snub-nosed monkey (R. roxellana), are known to vocalize in a ventriloquial manner, meaning that they do not need to open their mouths to do so. Though this hasn’t been documented in Tonkin snub-nosed monkeys, it may well be a capability of theirs as well. Other communication methods likely include body posturing and facial expressions, as well as olfactory communication—through smell.
Unfortunately, we know very little about the specifics of Tonkin snub-nosed monkey reproduction. However, we can glean the basics from its better-studied relatives. Tonkin snub-nosed monkeys likely have a polygynous mating system, in which each male mates with multiple females, but, for the most part, each female only mates with one male– occasional extra-group “affairs” notwithstanding. A female initiates copulation by presenting her rear end to her mate when she is receptive. Gestation lasts about six months, after which she gives birth to a single baby, usually at night. Among other snub-nosed monkeys, births tend to peak during times of the year when food is most abundant. Based on these species, the mother likely takes on most, if not all, parental care early on, though as the baby grows, other females in the group may help to provide care—a behavior called alloparenting. Although fathers do not tend to do much parenting, they have been observed to have a positive relationship with their young, tolerating their playful antics and protecting them from harm. Young snub-nosed monkeys begin to wean starting at a year old and are fully weaned by their second birthday.
As fruit eaters, Tonkin snub-nosed monkeys may help to disperse seeds of the plants they eat. Though their predators are not documented, they likely include animals such as birds of prey, wild cats, and civets, which are cat-like mammals.
The International Union for Conservation of Nature lists the Tonkin snub-nosed monkey as Critically Endangered (IUCN, 2015) appearing on the IUCN’s Red List of Threatened Species. They are truly teetering on the edge of extinction, with just 150-250 individuals believed to be remaining. In the last generation, about 12 years, they’ve experienced a 30% drop in population. Over three generations, or about 38 years, their population has dropped by 80%. However, the most recent data suggests that there may have been an uptick in the population over the last few years, sparking a glimmer of hope—a sign of the many dedicated conservationists who are working tirelessly behind the scenes to save the species.
The two main causes of Tonkin snub-nosed monkey decline are habitat loss and unsustainable hunting. Hunting pressure is the more immediate threat. Although Tonkin snub-nosed monkeys are not typically sought after by hunters due to their foul taste, they are shot opportunistically and sometimes targeted for use in traditional medicinals. In most areas where they live, hunting pressure is high.
Habitat loss and degradation have been caused by legal and illegal logging and gold mining operations, and, more recently, the development of hydroelectric infrastructure and the cultivation of black cardamom. A hydroelectric power operation along the Gam River in Na Hang is a recent development that has significantly impacted the habitat there. Increased human population in the monkeys’ range has resulted in increased human development and hunting pressure as well.
Black cardamom, or thao qua, is a spice that is common in Vietnamese cuisine and used in traditional Chinese medicine. Although it is grown in the forest subcanopy and does not involve clear-cutting forests, cardamom cultivation is environmentally intense. Its practitioners often practice “shade lopping”—the aggressive thinning of the canopy to maintain the right amount of shade and airflow for their plants—which significantly impacts the microclimates within the forest plot. Part of the cultivation process also involves drying the cardamom pods over a fire, so trees are felled to be used as firewood. This thinning of the forest, albeit less destructive than total clearing, still places a significant burden on the Tonkin snub-nosed monkeys, who rely heavily on “canopy pathways” for access to food resources and reproduction. The forest thinning required for cardamom cultivation has negatively impacted these canopy pathways, and, by extension, the monkeys themselves. While in more resilient habitats, cultivation of this type might be sustainable, it is unfortunately taking a toll on the critically endangered Tonkin snub-nosed monkeys that live nearby.
Tonkin snub-nosed monkeys are listed in Appendix I of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival.
Tonkin snub-nosed monkeys have been confirmed to live in two protected areas, the Na Hang Nature Reserve and the Khau Ca Species and Habitat Conservation Area of the Du Gia–Dong Van Plateau National Park, though there are unconfirmed reports of some groups living in other protected areas. The non-profit conservation group Fauna and Flora International has been heavily involved in conservation work in the Khau Ca area, supporting activities such as training community patrol groups, population monitoring, and conservation education. Fauna and Flora International has also joined with local research teams as well as the University of Colorado, the Denver Zoo, and the San Diego Zoological Society to enact long-term ecological studies in the habitat.
The Denver Zoo has also been involved in a surprising conservation initiative in Vietnam– promoting the use of “Rocket Stoves” to the local farming families living in and near the monkeys’ habitat. While this may seem entirely uncorrelated, Rocket Stoves are designed to use significantly less fuel than traditional stoves. This cuts down the demand for timber while also improving the quality of life for the local people. Less timber being cut down helps to preserve and protect the forest.
Recommended actions to further Tonkin snub-nosed monkey conservation include the establishment of new protected areas, habitat restoration projects, protection of important corridors between forests where the monkeys reside, population surveys to better understand where the monkeys live, and development of new livelihood models to help the local people improve their living standards while reducing their impact on the surrounding forests.
- Bach, L., Goldstone, R., Blanton, K., Harrison-Levine, A. 2023. Long-term partnerships offer hope for the “Critically Endangered” Tonkin snub-nosed monkeys (Rhinopithecus avunculus) of Ha Giang Province. Vietnamese Journal of Primatology 3(4):13-24.
- Boonratana, R. and L. Canh. 1998. Preliminary observations of the ecology and behavior of the Tonkin snub-nosed monkey (Rhinopithecus avunculus) in Northern Vietnam. In The Natural History of the Doucs and Snub-Nosed Monkeys 207-215.
- James, N. 2017. Cardamom sub-canopy crop cultivation threatens critically endangered Tonkin snub-nosed monkey (Rhinopithecus avunculus) in Vietnam. [Poster presentation]. Oxford Brookes University.
- Murugan, M., et al. 2022. Understanding the effects of cardamom cultivation on its local environment using novel systems thinking approach-the case of Indian cardamom hills. Front. Sustain. Food Syst. 6.
- Nguyen, T., Nguyen, D., Nguyen, X. 2023. An assessment of impacts of local communities on the habitat of the Tonkin snub-nosed monkey (Rhinopithecus avunculus) population in Quan Ba district, Ga Giang Province. VNU Journal of Science: Natural Sciences and Technology 39(2).
- https://www.iucnredlist.org/species/19594/17944213
- https://www.fauna-flora.org/projects/conserving-tonkin-snub-nosed-monkey-vietnam/
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- https://www.britannica.com/animal/snub-nosed-monkey#ref827559
- https://primate.wisc.edu/primate-info-net/pin-factsheets/pin-factsheet-golden-snub-nosed-monkey/
- https://www.ecologyasia.com/verts/mammals/tonkin-snub-nosed-monkey.htm
https://denverzoo.org/vietnam/
Written by K. Clare Quinlan, October 2024