Tonkin Snub-nosed Langur (Pygathrix avunculus)


MORPHOLOGY:
The Tonkin snub-nosed langur has a dental formula of 2:1:2:3 on both the lower and upper jaws (Ankel-Simons, 2000). The canines of the male are longer than the female's. This species has a digestive system that is designed for the fermentation of fibrous plants (Kay and Davies, 1994; Lucas and Teaford, 1994; Peng et al., 1983; Kirkpatrick, 1998). The stomach is enlarged and complex, and has bacteria to assist in the breakdown of fibrous plants (Kay and Davies, 1994; Lucas and Teaford, 1994; Peng et al., 1983; Kirkpatrick, 1998). This species also possesses enlarged salivary glands (Kay and Davies, 1994; Lucas and Teaford, 1994; Peng et al., 1983; Kirkpatrick, 1998). Adult of both sexes have upturned noses, with the tip nearly reaching the forehead. Adult males have an average body mass of 14.0 kilograms and adult females have an average body mass of 8.5 kilograms (Ratajszczak et al., 1992; Rowe, 1996). Adult males have an average head and body length of 65 centimeters and a n average tail length of 83 centimeters, and adult females have an average head and body length of 54 centimeters and an average tail length of 68 centimeters (Ratajszczak et al., 1992). The pelage color for the adult Tonkin snub-nosed langur is black with the hair of the inner limbs, thighs, face, and head is creamy white (Boonratana and Le, 1994, 1998a; Ren et al., 1996/1997). The tail is dorsally black and ventrally white (Boonratana and Le, 1994, 1998a; Ren et al., 1996/1997). On the throat there is an orange patch and around the eyes and nose the skin is bare and pale blue (Boonratana and Le, 1994, 1998a; Ren et al., 1996/1997). Around the mouth the skin is bluish-black (Boonratana and Le, 1994, 1998a; Ren et al., 1996/1997). The coloration around the mouth is thicker in adult males (Boonratana and Le, 1994, 1998a). Males have a black colored penis and a white colored scrotum (Rowe, 1996). Infants and juveniles have a pelage coloration that is gray rather than black (Boonratana and Le, 1994, 1998a; Ren et al., 1996/1997).

RANGE:
The Tonkin snub-nosed langur is found in the country of Vietnam. This species lives in primary rainforests on the steep karst mountains in northern Vietnam (Boonratana and Le, 1998b). This species has been also found to live in tropical evergreen forests (Kirkpatrick, 1998). This species is found in the provinces of Bac Thai and Tuyen Quang in Vietnam (Boonratana and Le, 1998b, 1994; Ratajszczak et al., 1992). Current records show this species to occur in the provinces of Bac Kan (Bac Thai have been split into two provinces: Bac Kan and Thai Nguyen), Tuyen Quang, and Ha Giang (Boonratana, pers. comm.*).

ECOLOGY:
The Tonkin snub-nosed langur eats young leaves, buds, bamboo shoots, seeds, and unripe fruit (Boonratana and Le, 1994, 1998b; Pham, 1993). Pham (1993, 1994) found that this species feeds on plants of 52 species belonging to 18 families, including Ficus, Polyalthia, and members of the family Euporbiaceae. Boonratana and Le (1998a) found that the diet of this species is primarily young leaves (38%) and fruits and/or seeds (62%). Ratajszczak et al. (1992) found that this species primarily feeds upon leaves. Food choice varies with the season with young leaves primarily eaten in the spring (February to May) and fruits primarily eaten in autumn (August to October) (Boonratana and Le, 1994, 1998a; Ren et al., 1996/1997). This is an arboreal and diurnal species (Boonratana and Le, 1994). The average group size at Na Hang was found to be 15.2 individuals (Boonratana and Le, 1998a). During windy winter days, sleeping sites are found low in trees that are found on steep mountains and are away from the wind (Boonratana and Le, 1994; Rowe, 1996).

A major predator of the Tonkin snub-nosed langur is humans, Homo sapiens (Boonratana and Le, 1998; Wirth, 1992).

LOCOMOTION:
The Tonkin snub-nosed langur moves through the forest quadrupedally (Fleagle, 1988). This species also moves by climbing, leaping, and brachiation (Boonratana and Le, 1994; Rowe, 1996). Traveling comprises 39.81% of total activity time (Boonratana and Le, 1998a). Moving between trees consists of leaping, hanging from branches and moving one arm in front of the other, and occasionally by brachiation (Boonratana and Le, 1998a). Only adults of either sex will be seen brachiating or hanging from branches and moving one arm in front of the other (Boonratana and Le, 1998a).

SOCIAL BEHAVIOR:
The basic group of the Tonkin snub-nosed langur is an adult male, one or more females, and their offspring (infants, juveniles, and subadults of both sexes), the uni-male group (Boonratana and Le, 1994; Le, 1994; Nguyen, 2000). All-male groups are also found made up of those adult males who do not have any adult females (Boonratana and Le, 1994). However, Ratajszczak et al. (1992) found that the Tonkin snub-nosed langur has a multi-male group structure. But this may be explained because several single male groups and all-male groups will come together for feeding, sleeping, and traveling, much like that found for Pygathrix brelichi and Nasalis larvatus (Boonratana and Le, 1994, 1998a; Bleisch et al., 1993; Yeager, 1989).

VOCAL COMMUNICATION:
long-distance call: This call is a doglike bark (Boonratana and Le, 1994; Rowe, 1996).

alarm call: This call sounds like a hiccup, or like huu chhhk (Boonratana and Le, 1994; Rowe, 1996). This vocalization can either be loud or soft (Boonratana, 1999). Recent observations suggest that this call in several contexts, including intra- and inter-group calling bouts (Boonratana, 1999).

OLFACTORY COMMUNICATION:

VISUAL COMMUNICATION:

TACTILE COMMUNICATION:
social grooming: This is when one individual grooms another and is used to reinforce the bonds between individuals. Grooming comprises 9.71% of total activity time, where 70% of that is social grooming (Boonratana and Le, 1994, 1998a). All members of the group participate in social grooming (Boonratana and Le, 1994, 1998a).

REPRODUCTION:
The Tonkin snub-nosed langur gives birth to a single offspring.

REFERENCES:
Ankel-Simons, F. 2000. Primate Anatomy. Academic Press: San Diego.

Bleisch, W., Cheng, A.S., Ren, X.D., and Xie, J.H. 1993. Preliminary Results from a Field Study of Wild Guizhou Snub-nosed Monkeys (Rhinopithecus brelichi). Folia Primatologica. Vol. 60, 72-82.

Boonratana, R. 1999. Fauna and Flora International - Indochina Programme: Na Hang Rainforest Conservation Project. FFI: Hanoi.

Boonratana, R. and Le, X.C. 1994. A report on the ecology, status, and conservation of the Tonkin snub-nosed monkey (Rhinopithecus avunculus) in northern Vietnam. WCS/IEBR: New York/Hanoi.

Boonratana, R. and Le, X.C. 1998a. Preliminary observation on the ecology and behaviour of the Tonkin snub-nosed monkey (Rhinopithecus [Presbyticus] avunculus) in Northern Vietnam. in The Natural History of the Doucs and Snub-nosed Monkeys. ed. N.G. Jablonski. World Scientific Publishing: Singapore.

Boonratana, R. and Le, X.C. 1998b. Conservation of Tonkin snub-nosed monkeys (Rhinopithecus [Presbyticus] avunculus) in Vietnam. in The Natural History of the Doucs and Snub-nosed Monkeys. ed. N.G. Jablonski. World Scientific Publishing: Singapore.

Burton, F. 1995. The Multimedia Guide to the Non-human Primates. Prentice-Hall Canada Inc.

Fleagle, J. G. 1988. Primate Adaptation and Evolution. Academic Press: New York.

Kay, R.N.B. and Davies, A.G. 1994. Digestive physiology. in Colobine Monkeys: Their Ecology, Behaviour and Evolution. eds. A.G. Davies and J.F. Oates. Cambridge University Press: Cambridge.

Kirkpatrick, R.C. 1998. Ecology and behavior in snub-nosed and douc langurs. in The Natural History of the Doucs and Snub-nosed Monkeys. ed. N.G. Jablonski. World Scientific Publishing: Singapore.

Le, X.C. 1994. New information about the Tonkin snub-nosed monkey Rhinopithecus avunculus in Na Hang forest. in A Management Feasibility Study of the Proposed Na Hang (Tonkin Snub-Nosed Monkey) Nature Reserve, Tuyen Quang Province, Vietnam. eds. C.R. Cox, V.D. Vu, M.G. Pham, and X.C. Le. Gland: IUCN Species Survival Commission.

Lucas, P.W. and Teaford, M.F. 1994. Functional morphology of colobine teeth. in Colobine Monkeys: Their Ecology, Behaviour and Evolution. eds. A.G. Davies and J.F. Oates. Cambridge University Press: Cambridge.

Nguyen, N. 2000. A survey of Tonkin snub-nosed monkeys (Rhinopithecus avunculus) in northern Vietnam. Folia Primatologica. Vol. 71, 157-160.

Peng, Y.Z., Zhang, Y.P., Ye, Z.Z., and Liu, R.L. 1983. Study on the stomachs in three species of snub-nosed monkeys. Zoological Research. Vol. 4, 167-175.

Pham, N. 1993. Some data on the food of the Tonkin snub-nosed monkey Rhinopithecus avunculus. Australian Primatology. Vol. 8(1).

Pham, N. 1994. Some data on the food of the Tonkin snub-nosed monkey (Rhinopithecus avunculus). Asian Primates. Vol. 3(3&4), 4-5.

Ratajszczak, R., Ngoc, C., and Pham, N. 1992. A survey for Tonkin snub-nosed monkey (Rhinopithecus avunculus) in the North Vietnam, March 1992. Gland: World Wildlife Fund for Nature.

Ren, R.M., Kirkpatrick, R.C., Jablonski, N.G., Bleisch, W.V., and Le, X.C. 1996/1997. Conservation status and prospects for the snub-nosed langurs (Colobinae: Rhinopithecus). Primate Conservation. Vol. 17, 152-159.

Rowe, N. 1996. The Pictorial Guide to the Living Primates. Pogonias Press: East Hampton, New York.

Wirth, R. 1992. Tonkin snub-nosed monkey (Rhinopithecus avunculus) rediscovered. Asian Primates. Vol. 2(2), 1-2.

Yeager, C.P. 1989. Feeding ecology of the proboscis monkey (Nasalis larvatus). International Journal of Primatology. Vol. 10, 497-530.

*pers. comm. stands for personal communication

Last Updated: June 22, 2007.
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