A survey of the distribution and population status of the capped langur (Trachypithecus pileatus) was conducted in and around the Pakke Wildlife Sanctuary in Arunachal Pradesh, India. From 2001–2003, we surveyed ten selected localities, recording 26 groups and a total of 195 individuals. The data was obtained using line transect surveys and total count methods. Capped langurs were found in a number of different habitats: tropical semi-evergreen forest and moist deciduous forests. Of the 195 individuals registered, 14% were adult males, 52% adult females, 2% unidentified adults, 7% sub-adults, 11% juveniles and 15%) infants. The smallest group numbered 3, and the largest 13, with an average group size of 7.5 individuals. The male-female ratio was 1:3.6. The most common size class of the group was of 7–9 individuals.
The capped langur occurs in northeastern India, Bangladesh, northwestern Myanmar, Bhutan and southern China (Zhang et al. 1981; Blower 1985; Stanford 1991; Ahsan 1994; Srivastava and Mohnot 2001). It lives in small groups, mostly single-male, multi-female, but occasionally with more than one male (Mukherjee 1978; Green 1981; Stanford 1991; Mukherjee et al. 1995). The species occupies a number of different habitats within its range including stands of bamboo, and plantations in northeast India (Choudhury 1989, 1996; Raman et al. 1995). Populations have been declining mainly due to habitat loss and degradation (Srivastava et al. 2001a, 2001b) and hunting (for food, medicinal purposes, and artifacts for socio-cultural practices and religious and cult ceremonies [Solanki 2002; Kumar and Solanki 2004]). Here we document the status, distribution, and group size and composition of capped langurs in and around the Pakke Wildlife Sanctuary, Arunachal Pradesh, India. We also report on human impacts on the species and their habitats in the sanctuary so that effective conservation measures can be formulated for the species in the region and particularly for the study area.
The Pakke Wildlife Sanctuary (PWLS) (formerly known as Pakhui Wildlife Sanctuary) is located between 92°35′ to 93°09′E and 26°55′ to 27°15′N, and covers 861.95 km2; 20% of the East Kameng district of Arunachal Pradesh (Fig. 1). It is bordered by Bhoreli River (or Kameng River) in the north and west, by Pakke River in the east, and by the Nameri National Park and Nauduar Reserve Forest of Assam in the south. The sanctuary is well drained by tributaries of the Bhareli and Pakke rivers. The topography is undulatinghilly and the altitude ranges from 200 to 2,040 m above sea level. The climate is tropical and subtropical; cold weather prevails from November to February. Average annual rainfall is 2,599 mm, and the annual mean (± se) maximum temperature is 31 ± 1.1°C, and the mean minimum temperature is 18± 1.2°C. There are four primates in the Pakke Wildlife Sanctuary—the rhesus macaque (Macaca mulatto), Assamese macaque (M. assamensis), the capped langur (Trachypithecus pileatus), and the Bengal or northern slow loris (Nycticebus bengalensis). The vegetation is Assam Valley type (2B/C1); tropical semi-evergreen with a high density and diversity of trees, woody lianas and climbers (Champion and Seth 1968). Tropical, semi-evergreen forests dominate the lower plains and foothills, while subtropical, broadleaved, evergreen and dense forests occur at elevations of 900 to 1,800 m above sea level. The Nyishi tribe lives around the sanctuary, one of the major elements of the human population living in the region, which also includes Nepalies, Kuli-bengalies and Bodo tribes.
A population survey was carried out at selected sites in and around the sanctuary over three years (2001–2003). We interviewed the sanctuary patrols, the range officer and the residents of peripheral villages for information as to the occurrence of capped langur groups in the area. A linetransect method was used to cover all areas in the sanctuary (Brockelman and Ali 1987). Total-count sampling was used in the areas of undulating terrain (NRC 1981). Repeat surveys were conducted on foot, recording group size and structure, sex ratio, vegetation type and any disturbances due to human activities such as settlements, grazing, logging, agriculture, hunting and poaching. Surveys were carried out by one researcher and two local guides from 06:00 to 11:00 and 14:00 to 18:00 or sunset. The langurs were classified into four age categories; adult, sub-adult, juvenile and infant based on the morphological differences described by Stanford (1991).
The surveys covered 201 km of transect in ten different locations (Table 1). Most of the groups sighted were at altitudes of around 800 m (26 groups), and mostly in tropical semi-evergreen forest and moist deciduous forests. Of the 26 groups, 20 were in the sanctuary and six were on the periphery. The maximum number of groups (4) and individuals (38) were recorded at Bhola Nallah Pung (Table 1). Groups ranged in size from 2 individuals to 13, with an average of 7.5 individuals per group.
The group structure and composition of capped langurs is shown in Figure 2. Nearly 90% of the population was recorded in one male—multi female social system. The malefemale sex-ratio for identified adults was 1:3.6. A group size of 7–9 individuals was most commonly sighted.
Demography of the villages and the livestock
Demographic information on the villages and livestock around the sanctuary, and who are dependent on the sanctuary for their daily needs, is shown in Table 2. We counted 37 villages, totaling 815 houses, 4,787 people in the surrounding area of PWLS. No human habitation was recorded inside the sanctuary. The number of cattle was 1,967, which generally use the buffer zone of sanctuary for grazing.
Numbers and average size of the groups and population density of capped langur.
Illegal hunting and the depletion of food plants important to the langurs due to the collection of non-timber forest produce (NTFP) were found to be the most serious threats (Fig. 3). Five capped langur groups totaling 37 individuals were recorded in December 2001 next to the eastern boundary of the sanctuary in Hatiputi area, which comes under the jurisdiction of Nauduar RF, Assam, but by the end of December 2002, the number had dropped to 13; twenty-four lost within a year (Kumar and Solanki 2004). Of these, four died due to accidents (two electrocutions, one bitten by a domestic dog and one fell out of a tree during ground foraging and social playing respectively) and the remaining individuals were hunted by tribal groups for bushmeat, ethno-medicine and socio-cultural practices (Table 3). They are also traded in local and external markets.
Extraction of plant resources
The plants exploited by the local people are shown in Table 4. A number of them are also important foods for the langurs. We recorded 37 plant species of 29 families being used by local people inhabiting the surrounding area of the sanctuary (Table 4). Of these, 21 were also used by the capped langur and other primate species in their diet (Kumar and Solanki 2003; Kumar 2006).
Capped langurs occupy all types of habitat inside and outside the sanctuary, but the tropical evergreen and semi-evergreen, deciduous forests with such trees as Ficus bengalensis, Ficus glomerata, Bombax ceiba, Altinga excelsa, Gmelina arborea, Morus levigata have been found to be important for the distribution of capped langurs in the region (Kumar 2006), and the availability of food trees may be a limiting factor (Joseph and Ramachandran 2003). Most of the langur groups recorded were between 400 m and 1,500 m above sea level. The largest numbers were recorded in the south-eastern part of the sanctuary, from Dichu to west of Tipi. Harwich (1972) argued that evergreen forest is necessary and is always present in the home ranges of this arboreal species.
Demographics of human and cattle's population around the Pakke Wildlife Sanctuary, Arunachal Pradesh, India.
Ethnozoological uses and trading of body parts of capped langur (Trachypithecus pileatus).
The size and composition of social groups varies geographically (Chivers and Raemakers 1980) because of habitat structure and food availability. Mukherjee (1978) recorded a group size of 7–13 for this species in the Manas Wildlife Sanctuary, Assam, and 5–16 in Tripura (Mukherjee 1982). In the Tinsukia district of Assam, Choudhury (1995/1996) recorded group sizes of 5–15 individuals. Disturbance, especially hunting, in the Pakke Wildlife Sanctuary may have been the cause of slightly smaller group sizes (2 to 15 individuals). Gupta (1994) recorded smaller groups, averaging of 5.7 individuals, in Gumati Wildlife Sanctuary, Tripura, and similar or slightly larger average group sizes have been recorded elsewhere in northeast India (9.7—Mukherjee 1978; 10.0—Choudhury 1995/1996) and Bangladesh (6.4—Islam and Husain 1982; 7.0—Green 1978; and 7–9—Stanford 1987, 1989). The average group size of capped langur is small when compared to other Indian colobine monkeys such as Trachypithecus. geei, T. obscura, T. johnii, T. phayrei, T. senex, T. vetulus, P. melalophos, Semnopithecus entellus, Presbytis thomasi, and Presbytis rubicunda (Table 5). Variation in group size in different habitats may be due to the difference in the distribution, abundance and quality of the food resources in the habitat and the population density.
Plants used by local people and included in the diet of the capped langur (Trachypithecus pileatus).
The Pakke Wildlife Sanctuary is also a tiger reserve; hence the core area is mostly free of biotic pressures except for the occasional organized hunting and poaching trips, as informed by the local hunters. Hunting, poaching and habitat destruction, is frequent in the adjacent forest areas of PWLS such as Hatiputi, Nauduar, Charduar reserve forests and Nameri National Park in the Sonitpur District of Assam (Choudhury 1996; Kumar and Solanki 2004; Kushwaha and Hazarika 2004).
Summary of different colobine monkey social systems.
Habitat destruction for agricultural activities, permanent settlement, fuel and fodder, and for minor forest produce is also a threat to the sanctuary, and has been since the mid 1990s. There has been an unprecedented number of encroachments by the Bodo tribe, involving clear felling of mature forests for agriculture and settlements in the area bordering the Nameri National Park (Assam) and Pakke Wildlife Sanctuary. Choudhury (2002) reported that reserved forested areas close to the sanctuary and Nameri National Park had been fully converted into agricultural lands and permanent settlements by the end of 2000. The macaques adapted, occupying nearby tea gardens and village woodlands, but the capped langur is now restricted to a few fragmented forests. Crop raiding began following this loss of habitat, as was also reported by Das (1998) in Tripura. The villages close to the sanctuary are using it for grazing; regularly sending large numbers of cattle into the forest there. Grazing pressure is highest from September to November in the sanctuary when agricultural fields are sown with paddy and others crops.
Capped langur, one of the most threatened primates of India due to hunting for their fur and Bushmeat, requires special attention for its long-term survival. The species is declining due to habitat loss and fragmentation and hunting in the entire distribution range of northeast India (Srivastava 2001a, 2001b; Kumar and Solanki 2004) and particularly in Arunachal Pradesh (Solanki and Chutia 2004; Kumar 2006). Preventing hunting and habitat destruction in these protected and non-protected areas is vital for protecting and conserving the species from extinction.
We are grateful to the Ministry of Environment and Forest, Government of India, for providing financial support for the study, and to the Department of Environment and Forest, Arunachal Pradesh for permission to work in the Pakke Wildlife Sanctuary and for logistical support. In particular, we thank the Director of NERIST for providing the necessary facilities and administrative and moral support for this work, Mr. C. Loma (Former Divisional Forest Officer, Pakke WLS) for guidance and support in the field, and Dr. Prabal Sarkar (Field Officer, WTI, New Delhi) for critical discussions.