Northern Plains Gray Langur, Semnopithecus entellus
NORTHERN PLAINS GRAY LANGUR
Semnopithecus entellus
Geographic Distribution and Habitat
The northern plains gray langur, also known as the Hanuman langur or Bengal gray langur, and scientifically as Semnopithecus entellus, can be found in a wide distribution across Eastern India. Their habitats are located North of the river Godavari and in areas south of the river Ganga. They also appear in Western Bangladesh due to human relocation. With an upper elevation limit of 1312 feet (400m), they live in a variety of environments. Northern plains gray langurs can be found in savannas, plains, shrublands, forests, and urban environments. While they inhabit a wide range of habitats, they are found primarily in human-dominated environments with varying population densities across regions. For instance, they have been found more densely populated in Gir National Park in Gujarat, India than in Orchha, India.
While the current state of the northern plains gray langur taxonomy is stable, there has been reclassification in the langur’s history. In the past, there was a distinction between the northern plains gray langur and the southern plains gray langur, which is now found to be an invalid taxon. Prior to the genetic testing that would prove no genetic difference between the northern and southern plain gray langurs, southern plain gray langurs were first classified as a subspecies and then as a separate species completely. Those individuals have now been absorbed into the northern plains gray langur species.
Size, Weight, and Lifespan
Sexual dimorphism is present in this species. This means there are apparent physical differences between males and females, other than their genital differences. Males are approximately 1.3 times the mass of their female counterparts. Males weigh between 37 pounds and 43 pounds (16.9 kg and 19.5 kg) while adult females weigh between 21 pounds and 35 pounds (9.5 and 16.1 kg). Their combined head and body length ranges from 17.8 inches to 31 inches (45.1cm to 78.4cm). Their tails can add anywhere from 31.6 inches and 44 inches (80.3cm and 111.8 cm). Notice that their tails are around 60% longer than their bodies!
Northern plains gray langurs can live up to their early 30s in captivity. Though males only live to about 18 in the wild, females can live to their late 30s.
Appearance
Northern plains gray langur fur is lightly tan or gray in color. They have darker fur on their back and limbs. The skin underneath their lighter fur is a darker brown, close to black. The face, ears, hands, and feet are all black due to the lack of fur in these areas. Infants are brown and turn the common gray-tan color as they age. Their tails are 60% longer than their body length and are non-prehensile, or non-grasping. These long light colored tails are primarily used for balance when traveling in the trees.
On their faces, eye color is a dark brown, and the corners of their mouth form a perpetual frown.
Diet
The northern plains gray langur is folivorous, meaning their diet mainly consists of leaves.
Most Colobines (the primate subfamily that includes the northern plains gray langur) have an enlarged and sacculated fore-stomach. Like cows and other ruminants—animals that graze on grasses and leaves, they have a pre-stomach compartment full of microbes. With the sac’s purpose of fermentation, these animals are able to break down plants and optimize the nutrients from a folivorous diet. These monkeys will often appear to have rounder bellies due to the gas from fermentation that occurs in the fore-stomach.
With their sophisticated digestive system, they are able to consume mature leaves that are much harder on the stomach than younger leaves. This allows them to fill an ecological niche. By having a diet that is more specialized and consuming tougher and potentially toxic plants than other animals in their ecosystem, they can easily find sources of food. They also eat fruits when available and will also consume other parts of plants, flowers, bark, and insects. Due to the langur’s close proximity to human environments, they may also feed on human crops or human food handouts (provisions).
Behavior and Lifestyle
The northern plains gray langur is diurnal, active in the day, and is both terrestrial and arboreal. They spend roughly an equal amount of time on the ground in the trees, interacting socially, foraging for food, feeding, resting, or playing.
Their behavior is largely dependent on their environment. Food acquisition can look like crop raiding, stealing, foraging, or even provisioning by humans. Due to their relation to Hanuman, the Hindu god, many people have fed troops of monkeys near temples and in backyards for generations. The monkeys in these environments spend less of their day worrying about food, engaging with other activities. Conversely, monkeys that steal their meals and raid crops are considered to be pests by local populations and increase tensions between humans and northern plain gray langurs.
Since food availability is so diverse across the species, different groups will spend varying amounts of their day interacting with each other, feeding, and napping. In more natural environments, food acquisition is a larger concern, with more time dedicated to it, while in urban areas, food is slightly more available.
Northern plains gray langurs are sometimes called “Hanuman langurs,” named after the Hindu god Lord Hanuman
Northern plains gray langurs have tails longer than their bodies!
They can have varying social structures from all-male groups, one-male and multi-female groups, to multi-male and multi-female groups.
Chital deer are in a symbiotic relationship with northern plains gray langurs: they work together to identify nearby threats using vocalizations.
Group life varies throughout this species. Unlike many other nonhuman primates that live in one or two types of social organizations, the northern plain gray langur lives in several different types of social groups. They can live in gregarious (multi-male and multi-female groups), polygynous (one male and multiple female groups), and multi-male and no female groups.
Group size can exceed 100 individuals, but is typically around 40 individuals. Males leave their natal group upon sexual maturity, and females are philopatric, meaning they stay in the group they were born into.
Males are dominant in this society, with an alpha male at the very top. Alpha males typically do not stay in their position for more than 3 years, but during this time will have an iron grip on the adolescent males of the group. Depending on the makeup of the group, the temperament of the alpha male, and the environment, he will either decide to cast out all sexually mature males or keep them around for safety against larger predators. Males do not groom one another, but females will groom both males and other females to increase group cohesion.
While the alpha male is the most dominant, many researchers say that the true power rests in the high-ranking females. They are the most well-fed of the group and regularly exercise their power over lower-ranking individuals. Younger sexually mature females are the highest ranking, with younger sisters outranking their older siblings. As females age and their fertility declines, their rank goes with it.
The northern plain gray langur has at least 19 different vocalizations. Loud calls or whoops are most often vocalized among harsh barks, cough barks, grunt barks, pant barks, grunts, honks, rumble, rumble scream, hiccup, and alarm calls. Whoops indicate the beginnings of movement and movement cessation in a social context. These calls can be heard well across the group area, and while whoops are unimportant to other animals, alarm calls to warn the group of predators can alert other species.
Chital deer are responsive to the northern plain gray langur alarm calls. Both animals work together to alarm the group of potential predators. Their collaboration may be due to the chital’s superior sense of smell and hearing in tandem with the northern plains gray langur’s vantage point from the trees.
Aside from vocalizations, body posturing and facial expressions serve as a form of communication. Presenting their body for grooming and “play faces” are examples of affiliative behaviors. High-ranking individuals will also swat at low-ranking monkeys to solidify their status or protect a food resource.
Reproduction is largely resource-dependent. Individuals in groups that live near and are provisioned by temples will reproduce year-round. All other groups in natural circumstances usually reserve their birthing period during December and May.
Gestation is 200 days, and the mother will give birth to one child, occasionally twins. After the birth, she is provided support by groupmates through alloparenting, in which other females in the group tend to the child. Other members of the group will raise the child with the mother during the 1st month of their life. Weaning occurs at approximately 1 year old, and males will reach maturity at 5 years of age. Females reach sexual maturity around 3 years of age.
Not unlike other nonhuman primate species, a male who has recently taken over a group may commit infanticide, the killing of infants sired by other males. This is partially to ensure that the dominant male’s offspring will not have to fight for resources. Primarily, though, it is because once an infant is killed, their mother leaves lactational amenorrhea (infertility during lactation/breastfeeding) and is fertile again. She can then bear the offspring of the dominant male faster than she would have been able to if her offspring were alive. To combat this, females in gregarious groups (multi-male and multi-female) will mate with as many males as possible to confuse paternity. If the newly dominant male does not know who his offspring is, he is less likely to kill an infant on the chance that the baby is his. While common, it is less likely to occur with a takeover that is drawn out over a couple of months.
Since northern plains gray langurs eat fruits, they disperse seeds through their feces, which helps maintain the ecosystem. Additionally, due to their semi-arboreal nature, they will drop some food resources to the ground, which are then picked up by their land-dwelling neighbors.
The northern plains gray langur is classified as Least Concern by the International Union for Conservation of Nature (IUCN, 2015), appearing on the IUCN Red List of Threatened Species.
Despite their classification, habitat loss caused by human agricultural development (monoculture plantations and tree felling), human and animal conflict, and invasive human settlements have negatively affected the northern plains gray langur. Hunting and trapping of these monkeys have also been recorded.
While the langurs are considered sacred in many parts of their habitat due to their connection with Hanuman, the Hindu deity, their lives have been severely disrupted by human interaction. They are also classified as pests and frequently raid crops, steal food, and disrupt human environments, further increasing tension with local residents. Natural predators are the tiger and dholes.
Northern plains 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. They are also protected locally under Indian and Bangladeshi wildlife protection and conservation laws.
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Written by Nami Kaneko, April 2025