Tarai Gray Langur, Semnopithecus hector
TARAI GRAY LANGUR
Semnopithecus hector
Geographic Distribution and Habitat
The Tarai gray langur (Semnopithecus hector), also known as the Hanuman langur, lesser hill langur, and Tarai sacred langur, is native to a small region in Bhutan, northern India, and Nepal, in the foothills of the Himalayan mountains and in the Siwalik Hills. They make their homes amongst the moist deciduous forests of the foothills and up into the oak forests of higher altitudes. They live up to an elevation of 5,250 feet (1,600 m). Tarai gray langurs must be able to adapt to two very distinct seasons: cold winters and hot, rainy summer monsoons.
The Tarai gray langur’s taxonomy has been in question since 1928, with a variety of modifications to its genus and its relationship to other Himalayan gray langurs. Some studies assert that all Himalayan gray langur species should be categorized together, as one species, under the common name “Himalayan gray langur” and the scientific name Semnopithecus schistaceus (the current scientific name for the Nepal gray langur).
In 2020, phylogenetic testing and morphological analysis studies determine that Himalayan gray langurs are split into multiple species, one of which is the Tarai gray langur. The others include the Kashmir gray langur (S. ajax) and the Nepal gray langur (S. schistaceus).
As the debate rages on, we shall continue to treat Tarai gray langurs as their own separate, distinct, and unique species.
Size, Weight, and Lifespan
Tarai gray langurs weigh about 28 pounds (12.5 kg), and their head and body length is about 24–27 inches (61–69 cm) in length. Their tails can add another 27–40 inches (69–102 cm). They live to be about 30 years of age in captivity. In the wild, females can live about this long, while males tend to have a shorter lifespan, closer to 20 years on average.
Appearance
Like other langurs, Tarai gray langurs have long, spidery limbs. They are overall a grayish-yellow color, with brown limbs, a gray-brown back, and a light gray belly, though overall, compared to other langur species, their body is largely uniform in color. In the right lighting, they can even look orange. Their face is bare and black, and framed with long white hair. Their tail is extremely long and skinny, longer even than their body. When walking on all fours, they tend to hold their tail over their back, with the tip pointing towards their head.
Diet
Tarai gray langurs are primarily folivores—leaf eaters. A large portion of their overall diet is composed of leaves, and supplemented with fruit, insects, flowers, and other plant parts. They even occasionally eat soil, which provides them with important minerals. Their diet varies heavily with the seasons—one study found that in the summer, leaves made up 67% of their diet, while in winter, they only made up 16%. The difference was made up with bark, buds, and plant stems, which they consume more in the winter than in the summer. In general, they are not picky eaters, eating what is available at a given time. Particularly important plants to the langurs’ diet are the bando lata or palas climber (Spatholobus parviflorus), baheda or beach almond (Terminalia bellirica), and karmal or dog teak (Dilleria pentagyna). While most of the water they need comes directly from the food they eat, they do occasionally drink sips of water as well.
Behavior and Lifestyle
Tarai gray langurs are diurnal, meaning they are awake during the day, and semi-terrestrial, meaning they spend part of their time—about 20% of it—on the ground. They move about on all four limbs, or quadrupedally, and they tend to prefer running to walking, or an unusual mix of the two—running for a few steps, then walking for a few steps. They are also known to hop on two feet and leap. They can cover 12–15 feet (3.7–4.6 m) while leaping horizontally, or up to 40 feet (12.2 m) while leaping downwards from a tree. While they don’t make a habit of it, gray langurs can also swim if they accidentally fall into a body of water.
During the day, Tarai gray langurs spend most of their time, about 40% of it, feeding, and about a third of their time resting. The remainder of their day is spent grooming other group members, moving around, vocalizing, and playing. In the summer, Tarai gray langurs are most active in the morning, before the heat of the day sets in, and in winter, they sleep in and are most active in the afternoon.
At night, Tarai gray langurs find a tree to sleep in, usually picking the tallest branches that can support them to settle in for the night. In areas with significant human encroachment and deforestation, they have been known to use electric poles for sleeping, which can be dangerous.
Tarai gray langur’s Latin name comes from The Iliad, the ancient Greek epic poem by Homer. Hector is the prince of Troy, and inspired the Tarai gray langur’s Latin name Semnopithecus hector. The Kashmir gray langur (S. ajax) and tufted gray langur (S. priam) are also named for characters from The Iliad.
Tarai gray langurs usually live in groups composed of multiple males and multiple females, with an average group size of 18 individuals. However, some groups have a single male and multiple females. Lone males sometimes congregate and form loose, all-male groups of up to five individuals. Home range size varies quite a bit, from 0.03 square miles (0.07 sq km) up to 8.5 square miles (22 sq km), with all-male groups typically having the largest home ranges. They travel about 0.9 miles (1.5 km) per day. Group members bond with each other through grooming—called “allogrooming”—and play. Play most often occurs between babies and juveniles and helps them to learn social behaviors and form bonds with one another. Mothers keep a close watch on their playing babies and occasionally step in to guide their social behaviors and to play themselves.
Tarai gray langurs communicate through a variety of vocalizations. They have loud whooping calls, grunts and coughs, and peeps, which are used when a group member gets separated from the others. Barks are used to alert group members to the presence of predators. When they are heard, group members immediately climb high into the trees to escape the predator. Allogrooming is also an important method of tactile communication within the group.
Tarai gray langurs are polygynandrous—meaning that males and females both mate with multiple partners. Females advertise their reception to mating by shaking their head and presenting their rears to adult males. Females are pregnant for about seven months before giving birth, which usually occurs in the first half of the year, from January to June, with births peaking in March. Single babies are almost always born, but twins do rarely occur. Pregnant females sometimes continue to copulate with multiple males to confuse paternity. Because males are protective of their offspring (or, at least, the young they believe could be their offspring), the babies then have the protection of multiple potential fathers.
Infants are cared for exclusively by their mothers for their first week of life, after which other new mothers in the group help to raise them. Babies begin to start eating on their own when they are about six weeks old, although true weaning won’t start until they are about eight months of age, and they aren’t completely weaned until they are over a year old. The babies are usually kept in the middle of the group for safety, and their mothers are fiercely protective of them, risking their lives to defend their babies if need be.
As they approach their first birthday, the young are largely independent and only spend about 20% of their time with their mother. They are considered fully independent when they are about two years old. Females reach sexual maturity at about three years of age, and males mature a bit later, at about five years. Females stay with the groups they were born into—their natal groups—while males leave when they reach sexual maturity. In captivity, female gray langurs are reproductively active for most of their life, into their late twenties, although it is unknown if this is true of wild langurs as well. They average about 2.5 years between births.
Wild cattle and deer have been known to wait under groups of gray langurs feeding in trees, waiting for dropped fruit. Larvae of the soapberry bug species, Leptocoris augur, rely on the langurs to crack open the hard casings of the fruit they eat. The langurs are likely preyed upon by animals such as leopards, tigers, and canines such as wolves, jackals, and dholes. They also play an important role as seed dispersers.
The International Union for Conservation of Nature lists the Tarai gray langur as Near Threatened (IUCN, 2015) appearing on the IUCN’s Red List of Threatened Species. It is suspected they have undergone a 20–25% population reduction over the past 36 years, or three generations.
The primary threats facing Tarai gray langurs are habitat loss, conflicts with humans, and hunting. Habitat loss has resulted in a very patchy distribution of the species. Instead of a vast, uninterrupted range, they instead are relegated to small patches of habitat as a result of human settlement.
Habitat loss is mainly caused by mining, firewood and charcoal production, and timber collection. Human conflicts include collisions with power lines, as well as conflict as a result of improper relocation. Langurs are hunted for meat, as well as for traditional medicine that is believed to cure a variety of diseases. There is no scientific proof of any benefits to these folkloric remedies.
Climate change is another potential threat to Tarai gray langurs in the coming years. Climate models predict that climate change will likely result in the shift of the langurs’ range to the east and an overall reduction of average habitat patch size of 58%. The areas that Tarai gray langurs are predicted to move to are not currently protected, meaning that more conservation action is needed in order to protect the future habitat of the species.
Tarai gray langurs are listed in Appendix I of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival.
It is unknown exactly which protected areas Tarai gray langurs occupy, though they are known to live in the Bardiya National Park, Rajaji National Park, the Valmiki Tiger Reserve, and the Corbett Tiger Reserve. Experts have identified several conservation actions that are the top priority for Tarai gray langur conservation. These include population surveys, habitat management, public education, monitoring, population management, and more research into the taxonomy and life history of Tarai gray langurs. Additionally, although hunting of langurs is prohibited by law in Nepal, the enforcement is limited. Better implementation of hunting laws is crucial to protect Tarai gray langurs.
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Written by K. Clare Quinlan, November 2023