Trachypithecus poliocephalus poliocephalus,
This beautiful and extremely rare colobine monkey is part of the genus Trachypithecus, in which the dark chocolate brown coat of adults contrasts spectacularly with the golden orange fur of infants, which turns to whitish-grey in juveniles (2) (3). The head and neck of adults are golden to yellowish-white in T. p. poliocephalus, with the pointed crest of hair on the top of the head being the most brightly coloured (3), and creamy-white in T. p. leucocephalus. A grey V-shaped area runs from the thighs to the back (3), and the fur of the pubic region ranges from white to pale orange (4). Adults are also adorned with a cape-like area of longer fur across the shoulders (3). The hands and feet are very slim, and the thumbs are notably shorter than in other primates (4
The Old World monkeys (family Cercopithecidae) are split into two subfamilies: the Cercopithecinae and the Colobinae, or colobine monkeys. As a colobine, the white-headed langur has large salivary glands and a complex sacculated stomach. This is an adaptation to the highly folivorous lifestyle of the leaf monkey or langur. Leaves are very difficult to process, requiring digestion by bacteria in the neutral upper chamber of the stomach before moving into the lower acid region. As well as consuming a large volume of leaves daily, the white-headed langur also eats fresh shoots, flowers, bark and some fruits. The very high concentration of fibre and tannic acids in this diet would be poisonous to many other species, including humans (3).
The white-headed langur lives in groups of about five to nine individuals (2), usually with just one dominant male (3). The group sleeps together in limestone caves, spending one or two nights in each one before moving on to another. There may be up to 12 resting caves in the range of a group, although rock ledges and tall trees are also used as sleeping sites, particularly in good weather. The group leaves the sleeping sites between 5 and 6:30 am according to season, and will spend a short time socialising before moving out to forage. Resting periodically through the day, the group makes its way towards the new sleeping sites as it feeds, settling down at around 5 or 6pm (3).
Females, who all mate with the only male of the group, give birth to a single, golden-orange infant. The majority of births appear to occur in April, but very little is known of the reproductive biology of this species. The young are thought to stay with their mother’s group for up to two years, before leaving to find or start a group of their own (4).
The Cat Ba langur (T. p. policephalus) is endemic to Cat Ba Island, the largest of more than 3,000 islands in Halong Bay off the northeastern coast of Vietnam (4). There is no evidence that this subspecies has ever lived on the mainland (3). The white-headed black langur (T. p. leucocephalus) is found in south China where it occupies seven karst regions in Guangxi Province. These regions are spread across three isolated, protected areas known as the Fusui Rare and Precious Animal Reserve, the Chongzuo Rare and Precious Animal Reserve, and the Longgang National Nature Reserve
Taxonomic Notes: It is unclear whether T. p. leucocephalus represents a subspecies or a distinct species, as some genetic evidence suggests they are as distinct as other recognized species. There are also obvious differences in coloration between the two. T. p. leucocephalus interbreeds with T. francoisi south and east of the River Zuo in Guangxi, China (Groves 2001).
voọc Cát B, voc , voc cat ba, hai phong