Tonkin Snub-Nosed Monkey, Rhinopithecus avunculus

TONKIN SNUB-NOSED MONKEY

Rhinopithecus avunculus

Geographic Distribution and Habitat

Presumed extinct before its rediscovery in 1989, the Tonkin snub-nosed monkey, also called Dollman’s snub-nosed monkey, is one of the world’s most endangered primates. Found only in northern Vietnam, this rare and elusive Old World monkey is one of two Rhinopithecus species found in Southeast Asia, the other being the newly discovered (in 2010) Burmese (or Myanmar) snub-nosed monkey (Rhinopithecus strykeri), who, like the Tonkin snub-nosed monkey, is already Critically Endangered.

As the only Rhinopithecus species to occur in subtropical areas, the Tonkin snub-nosed monkey’s range once included areas east of Vietnam’s Red River. Today’s populations of Tonkin snub-nosed monkeys are relegated to small areas within Tuyen Quang, Bac Kan, Ha Giang, and Thai Nguyen provinces.

The monkeys reside in primary forests (those that have remained undisturbed for a long time and have reached a mature condition) of broadleaf evergreen and bamboo. These forests are typically located on hilltops and mountains created from karst limestone (areas of irregular limestone in which erosion has produced fissures, sinkholes, underground streams, and caverns) at elevations between 656 and 3,937 ft (200 to 1,200 m). Monsoon rainfall and tropical temperatures further define the Tonkin snub-nosed monkey’s environment.

Tonkin Snub-nosed monkey range, IUCN 2008

Size, Weight, and Lifespan

The Tonkin snub-nosed monkey has the distinction of being Vietnam’s largest nonhuman primate. Males carry more girth than females, an example of sexual dimorphism (differences in appearance between males and females of the same species). An adult male Tonkin snub-nosed monkey weighs a robust 30 lb (13.7 kg), with females weighing a much daintier 18 lb (8.2 kg).

Head-to-body length in the species ranges from 1.67 to 2.13 ft (51 to 65 cm); the monkey’s tail adds another 2.17 to 3.02 ft (66 to 92 cm).

Compared to the four other species of snub-nosed monkeys—black snub-nosed monkey (Rhinopithecus bieti), gray snub-nosed monkey (Rhinopithecus brelichi), golden snub-nosed monkey (Rhinopithecus roxellana), and the Burmese (or Myanmar) snub-nosed monkey (Rhinopithecus strykeri)—the Tonkin snub-nosed monkey is more slender, is fitted with longer fingers and toes, and exhibits a lesser degree of sexual dimorphism.

Natural lifespan of Tonkin snub-nosed monkeys has not been recorded. The lifespan of wild colobine monkeys, who share the same subfamily, Colobinae, as Tonkin snub-nosed monkeys, is about 20 years.

Appearance

Mother nature has a sense of humor and flair. Or perhaps she had the day off and, in her absence, a makeup artist and a costume designer collaborated to create this most unusual-looking primate.

As the name indicates, a tiny upturned nose sits in the center of the monkey’s face. Pale blue rings encircle deeply set eyes. A hairless and flat, bluish-black triangle muzzle is stopped short by exaggerated pink lips that rival those of a circus clown. As if the lips were not pronounced enough on their own, they are outlined by bluish-black skin, which is darker in males. Creamy white fur adorns the face and trims the ears. A splash of orange fur, brighter in males, decorates the throat, adding contrast to the cream-colored fur on the monkey’s chest. Elbows, inner limbs, back of thighs, and the ventral side (underside) of the monkey’s long tail are also cream colored, with the tail ending in a creamy tuft. The back, outer limbs, hands, feet, and dorsal side (top) of the tail, which is accented by long strands of creamy-white hairs, are cloaked in black fur.

Variations in fur coat color and pattern have been reported among populations and individuals. There is some scientific speculation, however, based on museum specimens of this species, that color variations in the fur might be due to the monkeys’ contact with chemical preservatives or insecticides, combined with long exposure to sunlight.

Newborn Tonkin snub-nosed monkeys are cloaked in a grayish white or light-yellow fur coat, before grayish white patches develop on the back of their head and back. As older infants, these patches turn gray and remain so through the juvenile stage, eventually turning black when these monkeys reach adulthood. Similarly, the striking orange throat patch does not appear until adulthood, nor do the strands of white hair in the dark dorsal side of the tail. The blue-black “lip liner” is less pronounced in juvenile Tonkin snub-nosed monkeys.

In another example of sexual dimorphism, male Tonkin snub-nosed monkeys are fitted with larger canine teeth, on both the top and bottom jaw. And they have a black-colored penis with a white-colored scrotum.

Photo courtesy of ©Le Khac Quyet
Diet

Tonkin snub-nosed monkeys are largely folivorous, a fancy way of saying that they eat a lot of leaves—mostly from bamboo and evergreen trees. They eat a variety of fruits, too, making them frugivorous (another fancy term!). Seeds, both young and mature leaves, and flowers complement their meal plan.

The monkeys’ strong jaws help them to chew tough plant foods.

A specialized digestive system includes a sacculated stomach which aids in the digestion of leaves. Food is fermented in the stomach’s sack-like compartments, where bacteria slowly breaks down plant cellulose and counters any toxic substances, thereby providing the monkeys with more useable calories.

Behavior and Lifestyle

Tonkin snub-nosed monkeys are an arboreal and diurnal species, meaning that they spend most of their time in the trees and are active during daylight hours. They move through the forest canopy by walking on all fours (quadrupedally), climbing, leaping from tree to tree, hanging from tree branches, or by swinging from tree limb to tree limb using only their arms (a feat known as “brachiation”). In rare instances, the monkeys might walk upright (bipedally) along a supporting branch.

Researchers report that the monkeys spend almost 40 percent of each day resting, about 23 percent at vigilance (that is, on guard for potential threats), about 10 percent grooming one another (known as “allogrooming”), and about 3 percent in play. Tonkin snub-nosed monkeys construct their nighttime nests on a tree’s lower branches near a steep mountainside, for protection from cold winds.

Fun Facts

The Tonkin snub-nosed monkey is monotypic; that is, it has no subspecies.

Daily Life and Group Dynamics

Groups are organized into either all-male groups or groups with a single male and multiple females and juveniles. Foraging, feeding, and sleeping are activities performed as a group. In a phenomenon known as “fission-fusion,” groups might split into smaller groups (fission) to perform a specific activity such as foraging, and then come together again (fusion) once an activity is completed. Or, a group might temporarily join another group, forming a secondary level of social organization, for a specific activity. Scientists speculate that the Tonkin snub-nosed monkey’s propensity to a dynamic fission-fusion society suggests an intergroup tolerance and a lack of territoriality toward outside groups.

Home range size has been reported to be about 3.86 sq mi (10 sq km), and home ranges of different Tonkin snub-nosed monkeys often overlap. Range size suggests widely distributed food sources, and overlapping boundaries with other groups further suggests intergroup tolerance and a cooperation for food sources.

Communication

Vocalizations are the primary means of communication used by Tonkin snub-nosed monkeys. Their repertoire includes four distinct calls.

  • A soft “hoo” is sounded by individuals when they regroup after being separated because of a disturbance.
  • A soft “huu chhhk” is a contact call that sounds a bit like a hiccup, sounded by traveling individuals who are spread across a distance of 16.4 ft (5 m) or greater.
  • A loud and rapid “huu chhhk” is an alarm call that sounds like a loud hiccup, repeated by individuals when humans, or other potential threats, are detected.
  • A rapid “chit” is repeatedly sounded by individuals while fleeing unexpected encounters with humans or other potential threats.

In addition to vocalizations, allogrooming plays an important part in forming social bonds with one another. Scientists speculate that Tonkin snub-nosed monkeys may also use pheromones (chemical secretions) to communicate with one another.

Reproduction and Family

Male Tonkin snub-nosed monkeys reach reproductive maturity at about 7 years old. Females reach reproductive maturity earlier, at about 4 years old.

Scientists speculate that the social structure of Tonkin snub-nosed monkeys suggests a polygynous mating system (that is, the male or males mate with multiple females). But these monkeys are rare and difficult to observe; little research has been conducted on their romantic escapades (or their “reproductive behavior,” to be scientifically correct). Scientific conclusion about the monkeys’ reproductive behavior is based on one recorded observation.

Apparently, the female Tonkin snub-nosed monkey initiates copulation, enticing the male to “come hither” (follow her) as she leaps from branch to branch. As he approaches, the female moves her tail above and to one side of her body as invitation for the male to mount her. The male mounts the female from the rear, while positioning his feet firmly on a branch.

In the unromantic, sole scientific record of this perfunctory event, copulation lasted only 43 seconds. Afterward, the female moved to a neighboring tree and the male moved to a lower branch. Scientists report that the male then moved his forelimb in front of his face and briefly shook his head. No post-coital cuddling was observed.

If copulation proves reproductively successful, a female gives birth to one or two offspring after a 200-day gestation period, or just under 7 months. Births typically occur during the spring or summer. The breeding interval for Tonkin snub-nosed monkeys has not been reported.

Little is known about the level of parental care that Tonkin snub-nosed monkeys show their offspring. Because golden and black snub-nosed monkeys practice alloparenting (whereby other individuals in a group help care for one another’s infants), scientists conjecture that Tonkin snub-nosed monkeys might also practice alloparenting. And because the females of other snub-nosed monkey species are highly attentive to their young, scientists conjecture that female Tonkin snub-nosed monkeys (whom they are certain practice allogrooming with all other individuals in their group) are likely to be just as attentive to their young.

Ecological Role

Like other monkeys who are herbivores, Tonkin snub-nosed monkeys disperse seeds through their feces—thereby helping to regenerate their forest habitat.

Conservation Status and Threats

The Tonkin snub-nosed monkey is one of the most endangered primates in the world, with fewer than 80-100 mature individuals remaining. It is classified as Critically Endangered by the International Union for Conservation of Nature (IUCN, 2015), appearing on the IUCN Red List of Threatened Species. The species is also listed as Critically Endangered in the Red Data Book of Vietnam. And it has earned the ignoble distinction of appearing on the 2017 listing of “Primates in Peril – The World’s 25 Most Endangered Species.”

An October 2021 Facebook post by the Flora and Fauna International-Vietman Program stated the following: “From the initial number of 60 individuals in 2002, Tonkin snub-nosed monkey population at Khau Ca Species and Habitat Conservation Area (Ha Giang) has so far grown to about 160. The result comes from the local government’s will, local people’s participation and FFI’s efforts.”

Humans are the reason that Tonkin snub-nosed monkeys are on the verge of becoming extinct. This primate species has no other known predators, although scientists say arboreal snakes, large birds of prey, and wild cats might prey on these monkeys.

Intense hunting and massive habitat loss pose the biggest threats to the species’ survival.

Locals have traditionally hunted Tonkin snub-nosed monkeys as a food source, even though the monkeys’ flesh is reported to have a foul taste. Locals have also hunted the monkeys for use in folkloric medicines, which scientists state have no true medicinal value. Nevertheless, the monkeys’ dismembered body parts are traded in local markets and with neighboring China—despite conservation laws that deem this trade illegal.

A long history of logging, gold mining, and deforestation has had a cumulative and devastating impact on the Tonkin snub-nosed monkey population. Smaller subpopulations who live in fragmented, isolated areas are unable to interbreed, further jeopardizing the species’ survival.

In contrast, the local human population continues to grow. Settlements are being constructed within protected areas where these monkeys are known to live. And forestland is increasingly transformed into agricultural tracts of land.

The recent development of a hydroelectric project along Vietnam’s Gam River in Na Hang Nature Reserve has resulted in further habitat loss. With the construction of roads has come flooding and an influx of construction workers and a demand for wild meat. Monkey meat has shown up on the menus of Na Hang restaurants. 

Conservation Efforts

The Tonkin snub-nosed monkey is 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. In theory, the Tonkin snub-nosed monkey is also protected by Vietnam law, which prohibits the killing, capture, and trade of this species. However, as is often the case with endangered species, laws created to protect them are largely ignored and difficult to enforce.

Besides the Na Hang Nature Reserve, two other conservation areas—the Du Gia Nature Reserve and Cham Chu Nature Reserve—were established to protect the Tonkin snub-nosed monkey and its habitat. Yet hunting continues within these three “protected” areas and throughout the species’ range.

Conservationists warn that such blatant and continued disregard will be the species’ death knell. Fauna & Flora International, the Institute of Ecology and Biological Resources (IEBR), and other concerned conservation groups have put forth specific measures to save the Tonkin snub-nosed monkey from extinction. These measures include:

  • Additional surveys and continued research, conducted by field primatologists
  • The creation of trained patrol groups inside the nature reserves
  • Stricter law enforcement and heavier penalties for the illegal possession of protected species and their body parts
  • Enforced gun control laws
  • Expansion of protected areas
  • Habitat restoration
  • Consideration of a captive breeding program
  • Efforts to raise local awareness through education programs and active involvement in protecting the Tonkin snub-nosed monkeys

The importance of engaging the local community cannot be overstated. Conservationists know that getting local citizens to appreciate the natural resources of their environment, the values of biodiversity, and, specifically, saving the Tonkin snub-nosed monkey, is huge. But if their socioeconomic standards remain low—that is, if locals continue to struggle to earn a living—then awareness and education programs are not going to matter. So conservationists have come up with some innovative approaches to engage local citizens, improve their lives, and save the Tonkin snub-nosed monkey from extinction.

Foremost, conservationists attest that providing training and employment to local citizens—who are the primary “stakeholders” of the community, after the Tonkin snub-nosed monkeys themselves, is an effective way of ensuring support. Citizens could be offered positions as members of protection teams, monitoring teams, as field assistants on long-term studies, and as employees of the nature reserves.

Similarly, development projects (such as a hydroelectric dam) built close to protected areas should include a clause in employees’ contracts requiring employees to respect laws on species and habitat protection.

By tapping the skills and expertise of local citizens, giving them a role in helping save their environment and endangered species, and recognizing citizens with economic incentives, perhaps the Tonkin snub-nosed monkey will not disappear from our world.

In the words of one researcher, “conservation is primarily about a change in attitude.”

References:
  • Le, X.C. and R. Boonratana. 2006. A conservation action plan for the Tonkin snub-nosed monkey in Viet Nam. Hanoi/New York: IEBR/PCI.
  • Noel Rowe, Marc Myers, eds. All the World’s Primates, www.alltheworldsprimates.org. Primate Conservation Inc., Charlestown RI.
  • ​https://www.arkive.org/tonkin-snub-nosed-monkey/rhinopithecus-avunculus/
  • http://animaldiversity.org/accounts/Rhinopithecus_avunculus/
  • https://www.andieang.org/tonkin-snub-nosed-monkey
  • http://www.primatewatching.com/r-avunculus
  • http://www.iucnredlist.org/details/19594/0
  • https://www.fauna-flora.org/news/tonkin-snub-nosed-monkey-sighting-in-vietnam
  • https://en.wikipedia.org/wiki/Tonkin_snub-nosed_monkey
  • http://pin.primate.wisc.edu/factsheets/links/rhinopithecus
  • http://www.ecologyasia.com/verts/mammals/tonkin-snub-nosed-monkey.htm

Written by Kathleen Downey, February 2018