Nepal Gray Langur, Semnopithecus schistaceus
NEPAL GRAY LANGUR
Semnopithecus schistaceus
Geographic Distribution and Habitat
The Nepal gray langur, also called the central Himalayan langur, lives (as the name implies) in the Himalayan region, from central Nepal to Tibet, into areas of Bhutan, India, and Pakistan. They are the northernmost population of gray langurs, and they are one of only a few colobine species to live in temperate regions as opposed to tropical. They live up to an elevation of 13,000 feet (4,000 m), and their preferred habitat is temperate coniferous and broadleaf forests, although, in general, gray langurs are flexible about their habitat and can live successfully in a wide array of habitat types, even human-dominated areas such as cities.
The taxonomy of the Semnopithecus genus, the taxon of the gray langurs, is still unresolved. Until relatively recently, Nepal gray langurs were considered a subspecies of the northern plains gray langur, S. entellus. They, along with seven other langur species, are now considered to be separate species of the same genus. A 2019 study used molecular and morphological data to support the treatment of the Nepal gray langur as its own species, with no subspecies.
Size, Weight, and Lifespan
Nepal gray langurs are larger than most other gray langur species. The head and body together measure an average of 25 inches (69 cm) long, with males usually being slightly larger than females. This slight size difference is the species’ only sexually dimorphic trait. Males weigh, on average, 39 lbs (18 kg), and females weigh an average of 35 lbs (16 kg). In captivity, gray langurs often live into their early thirties. In the wild, males have been observed living over 18 years, and females have been seen to live over the age of 30.
Appearance
The Nepal gray langur has a brownish-gray body with a black face. The hair framing the face is long and stark white, and distinct from the body. The coloring difference between the head and the body is a physical trait that has justified the treatment of the Nepal gray langur as a unique gray langur species. For example, this differs from that of the northern plains gray langur for which the the head and body are a uniform color.
Hands tend to be dark brown or black, and bellies and chest tend to be light gray or white. They have long tails and fingers that are used to help move about in the trees. Interestingly, northern populations of gray langurs, which include Nepal gray langurs, tend to carry their tail pointed forward, while southern populations tend to carry their tail pointed to the ground. This is another morphological trait that has been used to justify the treatment of the Nepal gray langur as its own species, separate from the northern plains gray langur.
Diet
Although they are generally considered to be folivores (leaf-eaters), gray langurs are flexible in terms of their food consumption, adapting their diet to what is available during a given season. Their food choices may vary depending on habitat type, time of year, and proximity to humans. In general, their diet is composed of about 52–60% leaves, 15–25% fruits, and 9–16% other foods, such as insects and mosses. Nepal gray langurs also lick stones and consume soil to meet their nutritional requirements of salt and minerals, such as calcium and magnesium. Individuals living in close proximity to humans may even eat ashes and bones from cremation grounds to meet their nutritional needs. During lean winters, Nepal gray langurs eat mature evergreen needles, which are tough and low in nutritional value, so this is a food that is typically only eaten when little else is available. During the monsoon season, when insects are more abundant, the largely herbivorous (plant-eating) gray langurs eat significantly more insects than during other times of the year.
Their diet is rich in a neurotoxin called strychnine, which is a potent poison that comes from the strychnine tree. In order to counteract the effects of this chemical, these endlessly adaptive primates consume gum from the kulu tree. This gum contains a laxative that is commonly prescribed in human medicine today.
Most of the water intake by Nepal gray langurs comes from their food, although they also drink from pools, ponds, and rivers. Nepal gray langurs also drink water that has collected in tree holes—this is a behavior that was thought to be common in New World primates, but absent in Old World primates. However, recent observations from Nepal gray langurs and several other Old World species suggest that this may not be the case.
Behavior and Lifestyle
Gray langurs move about quadrupedally, and they tend to run instead of walk, although they sometimes switch between running and walking intermittently, traveling a few strides at a time at each gait. They spend about half of their time in trees and the other half on the ground. They may also hop bipedally and can leap horizontally up to 15 ft (4.6 m). While they are able to swim, this is usually only done if they accidentally fall into the water.
It has been proposed by some scientists that sightings of “yetis” in the Himalayan mountains may have simply been high-altitude-dwelling Nepal gray langurs.
Gray langurs are diurnal (active during daylight hours) and spend their nights sleeping in trees. They usually choose the highest branches that are available, and in human-dominated environments, even sleep on abandoned hunting towers and electric poles. Nepal gray langurs travel about 1 mile (1.6 km) per day, traveling longer distances in the winter. The home range size for gray langurs varies considerably, from about 0.03 to 8.5 mi² (0.07–22 km²). A typical day for a Nepal gray langur involves about 40% feeding, 29% resting, 18% traveling, 10% grooming, and 3% huddling, with the remainder dedicated to other miscellaneous activities.
Gray langurs live in several different types of social groups. These may be one-male groups, multi-male multi-female groups, and all-male groups. It is possible that multi-male multi-female groups may only be a temporary arrangement following a male’s takeover of a rival group. These groups may then split into one-male and all-male groups. Females remain in their natal groups and are related matrilineally, whereas males leave to join or form new groups upon reaching adulthood.
Dominance hierarchies are important to the group functioning of gray langurs. Males determine rank by chasing, fighting, and harassing others males to displace them. For females, rank is correlated to physical condition and age, with the youngest and healthiest sexually mature females ranking the highest. Relationships between females tend to be friendly, with frequent grooming, greeting, and embracing. Male and female relationships also tend to be cooperative, with females often grooming males. Male-male relationships are more turbulent, switching from peaceful to antagonistic as group dynamics change.
Gray langurs make a large variety of vocalizations, including barks signaling the presence of a predator, screams during aggressive group encounters, hiccups made upon sighting another group, and loud whoops made by adult males during reproductive displays.
In uni-male groups, the sole male is typically the father to all offspring. In multi-male groups, the highest ranking male sires most of the offspring, with lower-ranking males, and even males outside of the group, siring the rest. Females who rank higher tend to be more reproductively successful than lower-ranking females. Males are polygynous, mating with multiple females, and females, given the opportunity (i.e., if they do not live in a one-male group), are polyandrous, mating with multiple males.
Females invite copulation by shuddering their heads, lowering their tails, and presenting their anogenital region. Females have been observed mounting other females; it is unclear why, although it may be related to intrasexual competition. Females that are mounted by other females may be less inclined to solicit copulation by males, resulting in reduced sexual competition for the mounting females.
Gestation in gray langurs lasts for about 200 days, based on one population in Jodhpur, India. In populations that are provisioned (supplied food) by humans, reproduction occurs year round, while other populations reproduce seasonally. Females usually give birth to one offspring, although twins are not uncommon. They are usually born at night. Their first weeks of life are spent clinging to their mother’s chests and nursing or sleeping. After about two weeks, they are able to move more, and by six weeks, begin vocalizing more frequently. By the time they are three months old, they can walk, run, and jump. They continue nursing until they are about 13 months old. When they reach two years of age, other adult females in the group help to parent.
Gray langurs live sympatrically with other primate species, such as macaques and other langur species. This means that their territories overlap. Relationships between these species are sometimes mutually beneficial. For example, there have been instances of female gray langurs nursing rhesus macaque infants.
Gray langurs also have commensal relationships with other species, living in close association in a way that allows one species to benefit without harming the other. Food gleaning—whereby other species acquire unintentionally dropped food—is a common phenomenon between primates and hoofed mammals, and it has been observed between gray langurs and wild cattle and deer, who sometimes wait underneath feeding arboreal (tree-dwelling) gray langurs to consume the food that they drop. Gleaning from primates by carnivores, however, is rare, although it has been observed between the Nepal gray langur and the Himalayan black bear, which sometimes wait underneath beech trees to eat the nuts that are dropped by the monkeys. This is only the second observed instance of gleaning from a primate by a carnivore. Soapberry bug nymphs may also congregate near feeding gray langurs, as they crack open fruits that the nymphs then feed on.
Predators of gray langurs include leopards, tigers, wolves, golden jackals, and dholes, a type of wild dog.
Nepal gray langurs are an unusually flexible primate species, and as such, have adapted well as humanity’s impact on the natural ecosystem has increased dramatically in the last century. They are currently listed as Least Concern on the International Union for Conservation of Nature Red List (IUCN, 2015). Despite their relative stability, their population is decreasing.
Threats against Nepal gray langurs include habitat loss, disturbance from logging and fires, human expansion and encroachment, and war. Road mortality is a threat even within protected areas—a study at one wildlife sanctuary in India found that road mortality was the cause of 25% of langur deaths. Hunting of the Nepal gray langur occurs in China, as it is used in traditional Tibetan medicine. Conflict with humans is not common with this species, as it is considered sacred by some and because they are not typically aggressive towards humans. However, because some populations live in close proximity to humans, conflict may occur and the species is sometimes treated as a pest.
The Himalayan region is one of the most sensitive areas in the world to the effects of climate change. Already, the region is warming about three times faster than the global average, which is potentially catastrophic for the ecosystems and people of the Himalayan region. Expected effects of climate change in the region includes a drastic reduction in glacier, ice, and snow coverage, instances of increased river discharge resulting in landslides and flash floods followed by periods of drought, changes in plant blooming and leafing cycles, changes in predator-prey relationships, shifting tree lines, and changes in vegetation composition, among many others. These changes could cause Nepal gray langurs to face different predators, changes in food and water availability, natural disasters, new competitors, and many other changes. While generally considered a flexible species, these drastic changes could prove too severe for the species to adapt to.
This species is listed in Appendix I of the Convention on International Trade in Endangered Species (CITES). It is protected by at least ten protected areas throughout its range, including Dachigam National Park, Changthang Wildlife Sanctuary, Kanchanjunga National Park, and Everest Nature Reserve.
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Written by K. Clare Quinlan, November 2019