The Tonkin snub-nosed monkey or Dollman's snub-nosed monkey (Rhinopithecus avunculus) is a slender-bodied arboreal Old World monkey endemic to northern Vietnam. It has black and white fur, a pink nose and lips, and blue patches around the eyes. It is found at elevations from 200 to 1,200 m (700 to 3,900 ft) on fragmentary patches of forest on craggy limestone areas. First described in 1912, the monkey was rediscovered in 1989 but is exceedingly rare. Out of the five snub-nosed monkey species in the world, the Tonkin snub-nosed monkey is the rarest. In 2008, fewer than 250 individuals were thought to exist, and the species was the subject of intense conservation effort. The main threats faced by these monkeys are habitat loss and hunting, and the International Union for Conservation of Nature has rated the species as "critically endangered".
Description The Tonkin snub-nosed monkey has a flattened face with a pink upturned nose, thickened pink lips and areas of blue skin around its eyes. The upper parts are black, the underparts creamy-white, and there is an orange patch on the throat which is particularly obvious in breeding males. The tail has a white tip. Its head-and-body length is 51 to 65 cm (20 to 26 in) and its tail 66 to 92 cm (26 to 36 in). Females weigh about 8 kg (18 lb) while males weigh 14 kg (31 lb). Juveniles are grey rather than black, and lack the orange throat patch. Compared to the other four species of snub-nosed monkeys, the Tonkin snub-nosed monkey exhibits a smaller degree of sexual dimorphism. It is more slender and has longer fingers and toes.
Biology
Diet The Tonkin snub-nosed monkey's diet consists of a range of leaves, fruits, flowers and seeds. It is a largely folivorous species with its diet consisting mainly of leaves that come from bamboo and evergreen trees. The Tonkin snub-nosed monkey has a strong jaw which allows it to chew the tough plant-based food that is part of its diet. The monkey also has a specialized digestive stomach that aids in the digestion of its plant-based diet. Bacteria in the stomach break down plant cellulose and provide it with more calories that can be expended into more energy.
Reproduction The Tonkin snub-nosed monkey is a polygynous species, with one male mating with multiple females. Females reach reproductive maturity at about the age of four years old, while males reach reproductive maturity at about seven years old. A female can give birth to one or two offspring after a 200-day gestation period, with births typically occurring during the spring or summer months. It is speculated that female Tonkin snub-nosed monkeys are highly likely to be attentive to their young due to the observation of other female snub-nosed monkeys being attentive to their young. Tonkin snub-nosed monkeys are likely eaten by arboreal snakes and large birds of prey as well as forest cats.
Lifespan The typical lifespan recorded in colobine monkeys is about twenty years, with an age of twenty-nine years recorded in captivity. The lifespan of Tonkin snub-nosed monkeys has not been recorded as of yet.
Behavior Tonkin snub-nosed monkeys are diurnal creatures, meaning they are active throughout the day and sleep during the night. They often sleep on lower tree branches near mountain slopes, so as to provide a barrier against cold winds. The monkey moves about the canopy of the forest in small groups. The Tonkin snub-nosed monkey commonly lives in an extended family group that includes an adult male and several females, and their offspring. The family often comes together to sleep and feed, but sightings of families have become rare due to decreased habitat and population over the past years. Reports recorded by researchers have observed that these monkeys spend about forty percent of each day resting, about ten percent grooming one another, about twenty-three percent on guard for potential threats, and about three percent at play. It has also been observed by researchers, hunters, and local residents that the Tonkin snub-nosed monkey often does not flee immediately upon human detection. Instead the monkey begins emitting loud and rapid alarm calls, with the lead male of the group often approaching the people. This behavior places the Tonkin snub-nosed monkey at a higher risk of being killed by hunters.
Genetics A genetic diversity experiment based on mitochondrial information on the Tonkin snub-nosed monkey population in 2016 showed that there is a low amount of genetic variability in the population. This low diversity is likely a result of deforestation and intensive hunting of the species which led to population bottlenecks and restricted gene flow. A low amount of genetic diversity in a population is often associated with an increase in extinction, though there are examples of species that have persisted regardless of low genetic diversity.
Habitat The Tonkin snub-nosed monkey resides in primary forests which consist of bamboo and broadleaf evergreen. Recorded at elevations between 200 and 1,200 m (660 and 3,940 ft), its distribution is currently restricted to these forests which are located on hilltops and mountains created from karst limestone. The species' environment is also defined by its monsoon rainfall and tropical temperatures.
Ecological role The ecological role of the Tonkin snub-nosed monkey is very similar to that of other herbivorous monkeys, in that they disperse seeds through their feces and help to regenerate the forest environment.
Status
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