TARAI GRAY LANGUR
Geographic Distribution and Habitat
Tarai gray langurs occur in southwestern Bhutan (in Pankhabari), northern India (in Uttaranchal, Uttar Pradesh, and West Bengal), and southwestern Nepal (in Rajaji National Park) at elevations of 490–5,250 ft (150–1,600 m). They are very flexible in their habitat choices and can be found in a variety of habitats, from the moist deciduous forest of the Siwaliks to the oak forest of higher altitudes. Tarai gray langurs adapt well to habitats in close proximity to humans.
Other common names for the Tarai gray langur are lesser hill langurs and Tarai sacred langurs. Tarai gray langurs were formerly considered a subspecies of the northern plains gray langur (Semnopithecus entellus), but in 2001, it was suggested that seven distinct gray langur species should be recognized. Today, some scientists argue that there are only two broad species—southern gray langurs (who carry their tails looped backwards over their back) and northern gray langurs (who carry their tails looped forwards)—while others argue that some of the gray langurs, like the Tarai gray langur, that were upgraded to full species status in 2001 are actually still subspecies, but of the newly recognized Himalayan gray langur instead.
The Tarai gray langur’s taxonomy has been in question ever since 1928, when it was designated as a subspecies of Himalayan gray langur under Pithecus entellus, which became Semnopithecus entellus in 1939 and saw the removal of the taxon for the Tarai gray langur entirely. The Tarai gray langur remained forgotten up until 2001, when it was formally recognized as a species (not a subspecies) of Himalayan gray langur. Now, the debate has split into three separate arguments:
- There are various populations of Himalayan gray langurs within multiple subspecies under Pi. entellus, S. entellus, and P. entellus.
- The Himalayan gray langur is a distinct species that today includes Tarai gray langur, Kashmir gray langur (S. ajax) and the Nepal gray langur (S. schistaceus).
- Himalayan gray langurs are split into multiple different species (in this instance, the Tarai gray langur retains its species status).
A study from 2019 suggests that the latter argument is the most accurate given the data available for phylogenetic testing and morphological analysis (they arrive at the conclusion that there is no support for splitting the Himalayan gray langur into multiple subspecies), but a June 2020 article in Global Ecology and Conservation is suggesting that argument number two is the way to go and that all three species be grouped as the Himalayan gray langur with the scientific name Semnopithecus schistaceus.
As the debate rages on, we shall continue treat Tarai gray langurs as their own separate, distinct, and unique species.
Size, Weight, and Lifespan
Tarai gray langurs are mid-sized gray langurs, generally 20–31 inches (51–79 cm) in length with a tail anywhere from 27–40 inches (69–102 cm) long.
In captivity, gray langurs in general have been recorded living into their early thirties, but in the wild, males may live past eighteen years and the females live past thirty.
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Tarai gray langurs have a silky grayish-brown pale pelage all over their body and fairly uniformly colored limbs, whereas some other gray langurs have black hands and feet. Also unlike some other langur species, Tarai gray langurs lack crests on their head. The hair around their face is particularly white and fluffy. They have bare, darkly colored faces, ears, and fingers and long, skinny tails. Their eyes are round and brown, set into a face that has a seemingly permanent look of concern with a protruding snout and sunken cheeks.
They are often seen hunched over with their limbs tucked in as they rest in treetops.
Tarai gray langurs follow a folivorous diet, but they are not exclusively leaf-eating. For most langurs, diet is composed of leaves (52–61%), fruits (15–25%), flowers (4–13%), insects (0.4–3%), and other foods such as bark, gums, and soils (9–16%). Trees and shrubs are predominately consumed, followed by herbs, grasses, and other plant types.
Other potential foods consistent of shoots, seeds, mosses, lichens, coniferous cones, underground plant parts, spider webs, termite mounds, bamboo, cultivated plants (potatoes, spinach, and cauliflower), and food provisioned by humans (wheat cakes, millet).
Behavior and Lifestyle
Tarai gray langurs are arboreal (tree-dwelling), terrestrial (land dwelling), and diurnal (active during daylight hours). They move in a primarily quadrupedal (on all fours) fashion, both on the ground and in the trees, and they prefer running to walking. Langurs in general also hop, climb, and leap. Horizontal leaps have been observed between 12 and 15 ft (3.7–4.6 m) while descending leaps may be up to 35–40 ft (10.7–12.2 m). When moving terrestrially, gray langurs will sometimes switch off between walking, then running several steps, then walking again in an irregular pattern.
Tarai gray langurs are one of several gray langur species named after characters in Homer’s ancient Greek epic set during the Trojan war, The Iliad. The Latin name for Tarai gray langurs, S. hector, takes inspiration from Hector, the Prince of Troy. The other langurs named after characters in The Iliad are the Kashmir gray langur (S. ajax), named for the warrior Ajax the Greater, and the tufted gray langur (S. priam), named for Priam, the King of Troy.
Gray langurs, of which there are seven (debated) species, have the widest distribution of colobines; they are found in Bangladesh, Bhutan, China, India, Nepal, and Pakistan.
Tarai gray langurs live in multi-male, multi-female groups, though single-male groups do occur. They spend their nights in sleeping trees that stand an average of 39.4 ft (12 m) off the ground; Tarai gray langurs will usually select the highest branches to bed down in. In less natural habitats, gray langurs in general have used old hunting towers or electric poles for sleeping.
In the central Indian highlands, gray langurs spend their time feeding (25.7%), idle (41.8%), moving (13.1%), clinging (7.9%), and allogrooming (6%). In Nepal, Himalayan gray langurs spend their time feeding (39.8%), resting (29.2%), traveling (17.5%), grooming (9.5%), and huddling (3.2%), with the rest of their time spent on other activities.
Considering Tarai gray langurs live in both India and Nepal, it’s likely that their daily life looks like a combination of the aforementioned breakdown of activity, with feeding being the highest followed by resting and traveling or moving. In general, Tarai gray langurs do not follow a consistent daily regimen.
Generally, gray langurs communicate in a variety of ways and it is likely that Tarai gray langurs utilize some, if not all, of the following communication techniques:
- Loud calls or whoops made by adult males during displays
- Harsh barks made by adult and subadult males when surprised by a predator
- Cough barks made by adults and subadults during group movements
- Grunt barks made mostly by adult males during group movements and agonistic interactions
- Rumble screams made in agonistic interactions
- Pant barks made with loud calls when groups are interacting
- Grunts made in many different situations, usually agonistic
- Honks made by adult males when groups are interacting
- Rumbles made during approaches, embraces, mounts
- Hiccups made by most members of a group when they find another group
Female gray langurs signal that they are ready to mate by shaking their head, lowering their tail, and presenting their anogenital regions, but males do not always show interest in such displays. In captivity, female gray langurs have been observed as reproductively active well into their late twenties; it is likely that Tarai gray langurs have the same behavioral traits.
The gestation period for Tarai gray langurs lasts around 200 days. In some areas—especially those near human populations that provide gray langurs with a potentially constant food source—reproduction can occur year-round. Females give birth to a single infant, although twins do occur. Interestingly, most births take place during the night. Infants are born with thin, dark hair and they do not leave their mother’s side for at least two weeks. After six weeks, infants start to vocalize more and within two to three months, they can walk, run, and jump. By thirteen months, infants are weaned entirely.
Alloparenting—in which individuals other than the biological parents provide care to infants other than their own—occurs among gray langurs, mostly by other females in the group, though the biological mother shoulders most of the responsibility; if she were to die, it is likely her infant would follow soon after. On the flip side of alloparenting, infanticide is also fairly common among gray langurs, mostly by males that have recently joined a new group after driving out the previous male, especially in an instance of a one-male group. In multi-male groups, the risk associated with infanticide is higher, because the other males may intervene to protect the infants.
In some cases, wild cattle and deer wait under the trees where gray langurs feed in anticipation of dropped food. Tarai gray langurs also live symmetrically with a number of other primates, like the Nepal gray langur (Semnopithecus schistaceus).
Tarai gray langurs are listed as Near Threatened (NT) by the International Union for Conservation of Nature’s Red List of Threatened Species (IUCN, 2015). The population numbers are not known. The species is observed to have declined through many parts of its range and it has a very patchy distribution due to human settlements and habitat loss. A continuing decline has been observed in area and quality of habitat, and a decline is inferred in the number of threat-based locations and mature individuals. The population is considered to have declined by 20-25% over the past three generations.
Threats faced by Tarai gray langurs include mining, firewood and charcoal collection and production, timber collection, land distribution (resettlement), habitat loss, urbanization, and predation, including leopards, dholes, tigers, possibly wolves and golden jackals, snakes.
Tarai gray langurs are listed on the Convention on International Trade in Endangered Species (CITES) Appendix I and the Nepal National Park and Wildlife Conservation Act (1973) lists them as a common animal. It is difficult to know how prominent they are in protected areas because of their previous taxonomic uncertainty (as mentioned previously, they were thought to be a subspecies of the Northern plains gray langur), but they are known to occur in Rajaji National Park and Valmiki Sanctuary.
In order to better devise conservation efforts for this species in order to ensure their continued survival, the more research is needed in the areas of taxonomy, life history, and survery studies.
Management actions are also needed in the areas of habitat management, wild population management, monitoring, and public education.
Written by Rachel Heim, May 2020