Trachypithecus francoisi
Fran\\u00e7ois's leaf monkey

The family Cercopithecidae, or old world monkeys, includes leaf monkeys and langurs in the subfamily Colobinae. The subfamily has a wide geographical distribution throughout Asia and Africa. Trachypithecus francoisi, however, is found only in southern Guangxi province in China, northern Vietnam, and west-central Laos. (Helin, et al., 1999; Nowak, 1997; Tate, 1947)

An arboreal species, T. francoisi inhabits densely forested and limestone areas of tropical lowlands and forest valleys. Information regarding exact elevations occupied by these animals is unavailable. (Glover, 1938; Helin, et al., 1999; Nowak, 1997; Tate, 1947)

Though males of the species are slightly larger than females, T. francoisi are approximately two feet tall and weigh between 4 and 14 kg. Lengths between 400 and 760 mm are reported.

Pelage varies from uniformly brown, black, or dark gray with a white stripe running from the corner of the mouth to the ear. White is also present in a crest above the eyes, resembling eyebrows, a feature which distinguishes them from species in the genus Presbytis. Young are golden yellow with a black tail, another feature that distinguishes these monkeys from the black young of Presbytis.

These leaf monkeys have small heads and lack cheek pouches. The tail is long, straight, and black with a white tip. Forelegs are much shorter than hind legs with hairless hands and feet that allow easy grasping of branches. Thumbs are well-developed, opposable, and significantly shorter than the thumbs of Presbytis.

This species has not been studied extensively in captivity and information regarding metabolic rate is unavailable. (Glover, 1938; Helin, et al., 1999; Nowak, 1997)

It is common among colobines for females to initiate sexual behavior, and T. francoisi is no exception. Female proceptive behavior has been documented in the species, though specific information about this behavior is not available.

Trachypithecus francoisi is somewhat of an exception among other species in the family in that the social structure involves primarily one-male groups, in which one male mates with multiple females. Though it has not yet been observed in this species, other species in the genus are known to form all-male groups which occasionally attack one-male groups in order to oust the dominant male and take his place with the females. (Nowak, 1997; Nowak, 1997; Yeager and Kool, 2000)

Mating occurs throughout the year, peaking in autumn and winter. The frequency of breeding is unknown. The estrous cycle is 24 days and gestation lasts 6 to 7 months. A female delivers a single offspring once annually. The young are born fully furred and are fairly active. Animals become sexually mature after 4 or 5 years. The species has not been widely studied and the time to weaning and independence of the young is unknown. (Nowak, 1997; Yeager and Kool, 2000)

Female alloparental care of T. francoisi young has been documented and is a common trait among other Asian colobine species. It is hypothesized that alloparental care provides time and freedom for mothers to forage, improves parenting skills of the alloparent, and ensures the social integration of new infants to the group increasing the likelihood of adoption if the mother is killed. Additionally, it has been suggested that the infrequent but sometimes abusive handling of new infants by the alloparent reduces resource competition for the alloparents’ own offspring.

Other aspects of parental investment are unknown. However, in most primates with similar social structures, females provide the bulk of parental care. They groom, carry, and protect their young. However, males may also play some role in carrying, provisioning and protecting young. The most important parental role of males may be to protect young from potentially infanticidal rival males. (Yeager and Kool, 2000)

It has been recorded that this species does not survive well in captivity, but specific information is otherwise unavailable. (Collins and Roberts, 1978)

The arboreal T. francoisi is diurnal, and is extremely agile, adept at jumping from tree to tree. Individuals live in one-male groups of 3 to 10 individuals. Male members of the genus typically maintain their territories through loud vocalization and displays, though this has not been specifically observed in T. francoisi.

There are observations that a dominance hierarchy exists among the females of the species who seem to initiate socialization in the group. Female relationships within the group have been poorly documented due to poor visibility of the arboreal species; however, female-female affiliative behavior, allogrooming, sitting close to one another, as well as alloparental care previously discussed have been observed.

Groups generally exist peacefully; however, the leading male may experience territorial encounters with the males of other groups and may be ousted by an outside male. (Helin, et al., 1999; Nowak, 1997; Yeager and Kool, 2000)

These monkeys inhabit home ranges of about 157 hectares and the average daily range is about 1,000 meters. Population density per square kilometer is less than 45. (Nowak, 1997; Yeager and Kool, 2000)

Vocalization and visual displays have been observed in other members of the genus; however, little is know about the communication of T. francoisi. It is reasonable for us to assume that, as in other primates, visual, tactical, accoustic, and chemical communication are all used by these monkeys. (Yeager and Kool, 2000)

Trachypithecus francoisi feeds primarily on foliage, especially mature leaves, as well as some fruit and occasional insects. This low protein, high fiber diet requires a modified digestive system. The stomachs of monkeys in the Colobinae subfamily are large and multi-chambered. The forestomach hosts bacteria with cellulose-digesting abilities, allowing these mammals to process plant fibers. (Becher, et al., 2001; Davies, 1994; Glover, 1938; Helin, et al., 1999)

Little is known regarding adaptations to avoid predation, antipredator behaviors, or life history modifications as they might relate to predation of T. francoisi. However, a 1994 study suggests that species in this family are not limited by predation, except for being hunted by humans. (Davies, 1994; Isbell, 1994; Yeager and Kool, 2000)

The diet of primarily mature leaves is unique to T. francoisi, as other leaf eating monkeys prefer young leaves. Other than this impact on forest foliage, little is known about the role of these animals in the ecosystem. (Yeager and Kool, 2000)

Trachypithecus francoisi has been used in researching retroviruses that infect a variety of nonhuman primates and can be transmitted to exposed humans. The species is also hunted for its believed medicinal value. (Hussain, et al., 2003; Massicot, 2004; Tate, 1947)

Negative economic impact to humans, other than the possibility of a retrovirus transmittal, cannot be inferred from the available information. (Hussain, et al., 2003)

Trachypithecus francoisi is are listed as Endangered by the US Fish and Wildlife service, and the IUCN classifies the species as Vulnerable, with its status dependent on ongoing conservation efforts. CITES lists the species in Appendix I. The subspecies T. f. delacouri of central Viet Nam may be the most endangered monkey in Asia with fewer than 250 individuals alive. It has also been reported that T. f. leucocephalus in southeastern China has a population of only about 400, a result of hunting the monkey for its believed medicinal value. Populations of most other species of Trachypithecus are also declining due to loss of habitat.

Threats to the species include habitat loss to the expansion of agriculture, fuelwood harvesting, warfare, logging, and hunting. (Glover, 1938; Helin, et al., 1999; Massicot, 2004; Nowak, 1997)

Common names for the species include: capped leaf monkeys, langurs, leaf monkeys, brow-ridged langurs, and black leaf monkeys.

Trachypithecus francoisi was first noticed by M. Francois, the French Consul at Lungchow, Kwangsi, China, who found specimens on cliffs along the Longkiang River. He described flocks of small black monkeys with long tails and black heads. The species was first officially described by Pousargues in 1898 from specimens collected in Longzhou, southern Guangxi Province in China.

Trachypithecus was recognized as a separate genus by Eudey in 1987, but occasionally it is still considered a subgenus or synonym of Presbytis or of Semnopithecus. There are nine other species recognized in the genus: Trachypithecus vetulus, T. johnii, T. geei, T. pileatus, T. phayrei, T. cristatus, T. auratus, and T. obscurus. There is some debate over whether Trachypithecus leucoscephalus is a subspecies of T. francoisi or a distinct species. Recent DNA research suggests that it may in fact be distinct. (Ding, et al., 2000; Glover, 1938; Nowak, 1997; Tate, 1947)