Northern Plains Gray Langur, Semnopithecus entellus
NORTHERN PLAINS GRAY LANGUR
Geographic Distribution and Habitat
The northern plains gray langur (Semnopithecus entellus) is one of eight species of gray langur and is also known as the Hanuman langur, Bengal langur, or sacred langur. They are found across a wide area of India, south of the Himalayas. Northern plains gray langurs are also found in Western Bangladesh, although this population is believed to have been introduced by humans.
Northern plains gray langurs occupy dry and deciduous forest habitats as well as human-dominated landscapes. In fact, most populations are believed to occur in areas occupied by humans. They are considered sacred by some Hindus and the name “Hanuman langur” derives from the Hindu god Lord Hanuman. They are therefore left mostly undisturbed and even provisioned with food in some areas.
Size, Weight, and Lifespan
Adults have an average combined head and body length of 25.2 in (63.9 cm), generally ranging in size from 18–31 in (45–78.4 cm). Their long tails add another 27–40 in (69–102 cm). This species exhibits some sexual dimorphism; adult males are approximately 30% larger than adult females. Males weigh an average of 37 lb (16.9 kg), while females weigh an average of 26 lb (11.7 kg).
In captivity, northern plains gray langurs can live into their early 30s. In the wild, males generally reach only 18 years of age, while females can live over for 30 years.
The northern plains gray langur has a silver-gray pelage with a distinct, yellow tinge and black faces, fingers, toes, and ears. Unlike some other gray langurs, they do not have a crest. They have white hair around their faces and darker hair on their backs. Their bellies are a reddish-gold color. Young infants are brown in color and their pelage turns gray as they mature.
They have long, gray tails that are about one and a half times their body length and are used for balance and locomotion. Their wide mouths turn down at the sides, giving them a serious and somewhat sullen expression.
The diet of northern plains gray langurs varies based on region, most likely due to differences in food availability throughout their range. In general, they feed on seasonal fruits, flowers, and immature leaves from up to 150 different species of plants. Leaves usually account for about 50% of their diet and they have specially adapted digestive systems, which allow them to eat foods that are avoided by other animals, including seeds with high levels of toxins.
Langurs in urban areas are sometimes provisioned by humans and are given peanuts, breads, biscuits, and fruit.
Behavior and Lifestyle
Northern plains gray langurs spend approximately half of their time on the ground and half in the trees (or, in urban areas, tall man-made structures). They move in a quadrupedal manner (on all fours), using the palm of their hands, and tend to run instead of walk, both on the ground and in the trees. They are excellent climbers and can use leaping motions to move up and down structures. They are diurnal primates and will sleep at night in tall trees or sometimes on man-made structures, like telephone poles.
Daily life for the langurs can vary depending on the habitat they inhabit. For instance, troops that live in human-occupied areas and are provisioned by humans can spend less time searching for food and more time feeding and resting. Females spend more time grooming than males, which helps facilitate social bonds with their troop mates.
Northern plains gray langurs are sometimes called “Hanuman langurs,” named after the Hindu god Lord Hanuman.
They have a flexible social organization and can live in troops comprising all males, multiple males and females, or a single male and multiple females.
Originally considered one species, scientists now recognize eight species of gray langur in the genus Semnopithecus.
Northern plains gray langurs have a complex and variable social organization. Troops can either contain multiple females and one male (“one-male troops”), multiple females and multiple males (“multi-male, multi-female troops”), or only immature and mature males (“all-male bands”). Mean group sizes are 11–64 for troops and 2–17 for all-male bands.
Females are philopatric and stay in their birth group for life, whereas males leave their birth group around the age of sexual maturity (at approximately five years of age). They can then join either an all-male band, or a mixed-sex group if they have the opportunity.
The goal for all males is to monopolize a group of females; this is achieved by challenging a resident male and attempting to take over the group. These challenges can be vicious and can result in serious injury. The length of time that a male can monopolize a group can vary; some manage to fight off challengers for more than 10 years, but other males are ousted much more quickly by a new challenger. Researchers hypothesize that the reason that some males allow other males to remain in the group may be to help repel outside males in the event of a takeover challenge. However, males will sometimes join forces to chase a resident male out of a group and then fight among themselves to determine which male will take over the group.
Northern plains gray langurs use around 20 different types of vocalization to communicate with one another. These can include barks, grunts, alarm calls, and loud “whoops” made by adult males, which can be heard over one mile (2 km) away. Different calls can be used to coordinate group movement, during aggressive interactions, and to warn the group when a predator is sighted.
These langurs also communicate, like many other primates, by using different gestures and facial expressions. These include facial expressions such as the “play face,” which is used during play bouts to signal intention to play.
Reproduction in northern plains gray langurs is linked to food availability. Only when females can access enough food and are in a good enough condition are they able to reproduce. Therefore, the age at which a female first gives birth can range from 4 to 8 years, depending on the location. In areas with low food availability, breeding is seasonal.
Once a female is pregnant, the gestational period is approximately 200 days (6.7 months) resulting in the birth of a single infant, although twins are sometimes born. Allomothering. in which individuals other than the biological mother of an offspring perform the functions of a mother, sometimes occurs in this species.
Infanticide—the killing of an infant by a male—occurs in many (but not all) populations of northern plains gray langurs. This usually occurs when a new male takes over the troop and evicts the current male. Infanticide has likely evolved as a mating strategy for males, because females with young infants are not able to reproduce. However, if a new male kills her infant, a female will more quickly return to estrus and allow the male to mate with her. In multi-male groups, the females will mate with as many males as possible, which has likely evolved as a way to confuse paternity and help protect the infant from male infanticide.
Northern plains gray langurs play a role in seed dispersal. Since fruit is a key part of their diet, they aid seed dispersal by ingesting and then scattering the seeds once the seeds have passed through their digestive system. Deer and cattle are known to eat food that the langurs drop to the ground whilst foraging.
The northern plains gray langur is classified as Least Concern by the International Union for Conservation of Nature (IUCN, 2015). However, their population is thought to be decreasing. Their natural habitat is threatened by slash-and-burn agriculture, grazing, and open cast mining. Although these langurs are traditionally considered sacred, as their habitat diminishes they will compete more with humans for resources and this will likely lead to greater levels of human-wildlife conflict. Langurs sometimes engage in crop-raiding or steal food from human homes and businesses; an increase in these behaviors will likely lead to greater persecution of this species. Predators can include tigers and dholes.
Northern plains gray langurs are listed as Appendix I of the Convention of International Trade in Endangered Species (CITES). It is illegal in India to capture of kill these langurs; however, enforcement is difficult and many people remain unaware of the laws surrounding this species.
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Written by Jennifer Botting, October 2019