The distribution of R. avunculus is restricted to northern Vietnam. This is one of the most endangered primate species in Asia; it is classified as ‘critically endangered’ (IUCN 2002). The langurs are found in subtropical forests on steep karst limestones, with tree species ranging from figs and dipterocarps to oaks, magnolias and maples. The forests show substantial seasonality: between February and May, for example, the forests are flush with young leaves, while between August and October, many of the trees synchrously bear fruits. R. avunculus is limited to at least four subpopulations, with a total population size of approximately 250 individuals.
R. avunculus appears to follow the colobine tendency to be completely arboreal. Social organization is based on one-male, multi-female units (OMUs), but all-male units (AMUs) are seen as well. Different OMUs frequently come together at sleeping sites and feeding trees, and OMUs at times travel together. The diet consists primarily of leaves (including the leaves of bamboo) and fruits, and food choice varies with the seasons: young leaves are a primary component of the diet in spring, and fruits are a primary component of the diet in autumn.
This species is sometimes also called “oxtailed snub-nosed monkey” due to the shape of the tail. It is distributed only in a small region centering on Mt. Fanjing in the Wuling Mountains of China’s Guizhou Province. The langurs generally range in a zone of mixed deciduous and evergreen broadleaf forest between 1’500 and 2’200 m. Temperatures fall below freezing during five months of the year, and snows are common in winter. Within the forests used by the monkeys, often mono-groves of Asian oaks and beech occur, but there are other forest types used by the langurs without a dominant tree species. Common canopy trees include cherries, maples, Rhododendron ssp., and birch. The world population of R. brelichi is about 700, all in a single population. This species is classified as ‘endangered’ (IUCN 2002).
R. brelichi is primarily arboreal, and locomotion is characterized by quadrupedal walking, climbing, leaping, semi-brachiation and occasionally by full brachiation. Social organization appears to be based on small groups of 5 to 10 individuals, each with a single male. A large number of these OMUs range together in a large, semi-cohesive band that probably holds up to 400 individuals or even 700. Large-scale fission-fusion appears to occur on a seasonal basis. AMUs of 2 to 5 adult or subadult males are seen on the periphery of these bands. The langurs use a wide variety of food resources, with dramatic changes through seasons. Foods include deciduous and evergreen leaves and leaf buds of many species, leaf petioles, flower buds, fruits and seeds, bark, lichens, insect larvae, bird eggs and soil.
R. roxellana has the widest distribution of any species of snub-nosed langurs, being found in the Qionglai Mountains of Sichuan, Min Mountains of Sichuan and Gansu, Qinling Mountains of Shaanxi and Daba Mountains of Hubei. The forests used by the langurs range in elevation from 1’200 to over 3’000 m and consist of three main types: deciduous broadleaf forest, conifer forest and mixed forest. The world population is estimated to be 8’000 and 10’000 animals, but according to very recent press releases (2003) the numbers are higher, especially in Gansu Province. R. roxellana is classified as ‘vulnerable’ (IUCN 2002). The genetic diversity of wild populations of R. roxellana is extremely low, possibly due to a recent bottleneck.
R. roxellana is both arboreal and terrestrial, spending almost half of its time on the ground. Daily travel distances and home range sizes vary between seasons. The social organization is similar to other species of Rhinopithecus with the size of bands spanning 50-500 individuals or more. The basic social unit within the bands is the OMU, although bands can have a few multi-male, multifemale units (MMUs); AMUs also are associated with bands. Bands of R. roxellana are characterized by a fission-fusion system. Bands at times separate into 2 or 3 smaller groups during the day, with these smaller groups staying at a distance from each other of between 200 to 300m. It is as yet uncertain if there are distinct daily or seasonal patterns of fission-fusion, however. The diet of R. roxellana fluctuates widely across seasons, and consists of leaves, seeds, buds, bark, insects under the bark, fruits and lichens.
A Chinese local name for R. bieti is “xuehou”, meaning “snow monkey”. R. bieti used to be considered as a subspecies of Pygathrix roxellana, but is now regarded a full species. In fact, the separation between R. roxellana and R. bieti may only have occurred quite recently in the Middle Pleistocene following the dramatic uplift of the Qinghai-Tibetan plateau and its adjacent areas, the Hengduan Mountains. R. bieti was discovered by French scientists in 1871 in Yunnan, and Milne-Edwards made the first formal report. This taxon is classified as ‘endangered’ following IUCN (2002). The genetic diversity of R. bieti estimated by protein electrophoresis was found to be very poor, and it is assumed that R. bieti experienced a ‘bottleneck effect’ in the past.
The morphology of Yunnan snub-nosed monkeys is characterized by a considerable sexual dimorphism between males and females. In many parts of its natural habitat, this species is secretive and elusive. It is found between longitude 98°37’ to 99°41’ and latitude 26°14’ to 29°20’ along the Yunling Mountains (part of the Hengduan Mountains) in the Eastern Himalayas of Northwest Yunnan (Deqin, Weixi, Lijang, Lanping, Yunlong Counties) and East Tibet (Mangkang County) where the rugged terrain makes field observations an extremely difficult task. Furthermore, due to the large group sizes of R. bieti, it is impossible to individually recognize group members; this drawback has hindered in depth studies on social behavior. Thus, the mechanisms that hold the social group of this species together, are still largely unexplored. Most field studies have focused on ecological questions. The langurs are found in high-altitude, mostly evergreen forests, with the canopy composed primarily of fir (Abies spp.), spruce (Picea spp.), evergreen oak (Quercus spp.), intermingled with Rhododendron spp. and, especially in the south, dense bamboo patches (Fargesia spp.). The ranging area lies between 2700 and 4600 m, making R. bieti the non-human primate living at the highest known elevations. Temperatures fall below zero for several months of the year, and snow can accumulate to over 1 m in depth in the north (Kirkpatrick 1996). The species’ distribution is bounded by the upper rivers of Yangtze to the east and Mekong to the west. From north to south, temperature, precipitation and diversity of vegetation increase in line with a decrease of the elevational profile. Recent surveys indicate that the total population size of R. bieti lies somewhat between 1200 and 1700 animals, found in 13 subpopulations. Due to human population growth, the habitat has been reduced and fragmented which resulted in a sharp decline of the population numbers and several extinct subpopulations in recent time.
R. bieti is semiterrestrial, spending between 20 and 70% of the day on the ground. Compared with other colobines, range use is large and daily travel distances long. Social organization is two-tiered. OMUs range together as bands, with the size of bands apparently spanning from under 20 to over 360 individuals. AMUs exist as well. Unlike the bands of other members of the genus, however, bands of R. bieti do not show longterm fission-fusion. The primary foods of R. bieti appear to be arboreal lichens and broad-leaves and, at certain times of the year, the foods are supplemented by fruits and seeds. Differences in food choice between study sites are considerable.